PEGylated organosilica nanoparticles have been synthesized through self-condensation of 3-mercaptopropyltrimethoxysilane in dimethylsulfoxide into thiolated nanoparticles with their subsequent reaction with methoxypolyethylene glycol maleimide. The PEGylated nanoparticles showed excellent colloidal stability over a wide range of pHs in contrast to the parent thiolated nanoparticles, which have a tendency to aggregate irreversibly under acidic conditions (pH
Keddie JL, Meredith P, Jones RAL, Donald AM (1995) Kinetics of film formation in acrylic latices studied with multiple-angle-of-incidence ellipsometry and environmental SEM, Macromolecules 28 (8) pp. 2673-2682
A combination of multiple-angle-of-incidence ellipsometry (MAIE) and environmental SEM (ESEM) was used to characterize the microstructure of acrylic latices during all four stages of film formation, starting from an aqueous colloidal dispersion (Stage I) and evolving to a continuous coating having no internal solid-solid interfaces (Stage IV). Stage II is usually defined as a close-packed array with water-filled interstices, and Stage III is defined as a densely packed array of deformed particles. This analysis identified an additional stage, II*, intermediate to the conventionally defined Stages II and III. The onset of this new stage, which coincides with the development of optical clarity, occurs at nearly the same time (normalized by the final film thickness), regardless of the glass transition temperature (Tg) of the latex polymer. The duration of Stage II* and the kinetics of particle coalescence in Stage III, on the other hand, are a function of Tg. A latex with a Tg well below the ambient temperature can deform rapidly to fill the space left by the evaporation of water. A latex with a higher Tg cannot, and so air voids and surface roughness develop and persist over measurable times.
Parbhoo B, Izraej S, Salamanca JM, Keddie JL (2000) Use of ellipsometry and gravimetry to develop calibration standards for measuring silicone coat weight and thickness with x-ray fluorescence spectroscopy, Surface and Interface Analysis 29 (5) pp. 341-345
There are important technological and scientific needs for accurate and precise measurements of the weight and thickness of silicone coatings, which are used in wide-ranging applications. X-ray fluorescence (XRF) spectroscopy offers one means of achieving such measurements. Here we show that, as predicted from theory, the intensity of the XRF intensity is linearly proportional to the thickness and weight of a relatively thin silicone coating on a poly (carbonate) substrate. This linear relationship is demonstrated using both gravimetry and spectroscopic ellipsometry to provide two independent measurements of coating thickness, resulting in a robust method for the calibration of the XRF intensity. Copyright © 2000 John Wiley & Sons, Ltd.
© 2015 American Chemical Society.The conventional method for synthesizing waterborne polymer colloids is emulsion polymerization using surfactants. An emerging method is the use of secondary dispersions (SD) of polymers in water, which avoids the addition of any surfactant. Although there are numerous studies of the water barrier properties (sorption, diffusion, and permeability) of waterborne emulsion (Em) polymer coatings, the properties of SD coatings, in comparison, have not been thoroughly investigated. Here, dynamic water vapor sorption analysis is used to compare the equilibrium sorption isotherms of the two forms of styrene-acrylate copolymers (Em and SD) with the same monomer composition. From an analysis of the kinetics of vapor sorption, the diffusion coefficient of water in the polymer coatings is determined. The combined effects of particle boundaries and surfactant addition were investigated through a comparison of the properties of SD and Em coatings to those of (1) solvent-cast polymer coatings (of the same monomer composition), (2) Em polymers that underwent dialysis to partially remove the water-soluble species, and (3) SD polymers with added surfactants. The results reveal that both the particle boundaries and the surfactants increase vapor sorption. The diffusion coefficients of water are comparable in magnitude in all of the polymer systems but are inversely related to water activity because of molecular clustering. Compared to all of the other waterborne polymer systems, the SD barrier coatings show the lowest equilibrium vapor sorption and permeability coefficients at high relative humidities as well as the lowest water diffusion coefficient at low humidities. These barrier properties make SD coatings an attractive alternative to conventional emulsion polymer coatings. (Figure Presented).
Neutron reflection (NR), spectroscopic ellipsometry (SE), and atomic force microscopy (AFM) have been used to characterize the structure of self-assembled octadecyltrichlorosilane (OTS) layers on silicon. The first two of these techniques rely on modeling of the experimental data and may thus result in the unrealistic representation of the composition and structure at the interface. Ambiguities arise from model-dependent analysis complicated by the lack of sufficient external constraints to converge nonunique solutions to a unique one. We show in this work that AFM measurements provide extra constraints to allow us to obtain a physical description closer to the actual structure of the film. It was found that ?the simpler the better? modeling strategy very often employed during the fitting of ellipsometric and neutron reflection data is, therefore, not necessarily the best way to obtain a reliable description of the interfacial structure. Our AFM findings necessitated the refit of both neutron and ellipsometric data that were previously described by a single-layer model. Interpretation of the structure of thin layers that is based only on indirect measurements such as SE, NR, and x-ray reflection techniques may be, therefore, misleading. A combined analysis of SE, NR, and AFM data suggests that the OTS film may comprise a rough layer, with pinholes down to bare silicon oxide surface, consisting at least of mono-, bi- and trilayers of OTS molecules.
Deplace F, Marchal J, Carelli C, Chateauminois A, Creton C, Rabjohns M, Foster A, Lovell PA, Lei C, Keddie J (2009) Soft-soft nanocomposites for adhesive applications, 12th International Conference on Fracture 2009, ICF-12 2 pp. 1205-1211
Daar E, Kaabar W, Lei C, Keddie JL, Nisbet A, Bradley DA (2010) AFM and uni-axial testing of pericardium exposed to radiotherapy doses, Nuclear Instruments and Methods in Physics Research, Section A: Accelerators, Spectrometers, Detectors and Associated Equipment 652 (1) pp. 874-877 Elsevier
Mallégol J, Keddie JL, Dupont O (2001) Etude structurale des films d'adhesifs acryliques sensibles a la pression par microscopie a force atomique en mode tapping, Vide: Science, Technique et Applications (302 SUPPL.) pp. 34-37
Holl Y, Keddie JL, McDonald PJ, Winnik WA (2001) Drying modes of polymer colloids, ACS Symposium Series 790 pp. 2-26
This chapter reviews the complex step of drying in the latex film formation process. Drying modes have a profound effect on drying rates and on the final properties of films, primarily through their influence on film morphology and the distribution of water-soluble species. Three distinct drying modes (acting separately, successively or together) can be defined, namely homogeneous drying (in which the water concentration remains uniform in the sample throughout the drying process), drying normal to the surface (where a dry layer of increasing thickness develops from the air surface of the latex coating); and lateral drying (where dry areas increase in size in a direction parallel to the substrate). Details are given on the current knowledge and understanding of these drying modes. The last section of the chapter considers the main parameters controlling the drying modes, i.e. thickness and geometric effects, the structure and rheology of the dispersion, particle viscoelasticity, and the overall rate of water loss.
In films cast from a colloidal dispersion comprising two particle sizes, we experimentally examine the distribution of particles normal to the substrate. The particle concentrations at various positions in the film are determined through atomic force microscopy and NMR profiling. The results are compared to a previously derived diffusional model. Evidence for diffusional driven stratification is found, but the importance of other flows is also highlighted. The conditions that enhance particle stratification are found to be a colloidally stable dispersion, low initial volume fractions, a low concentration of the stratifying particle, and for the Peclet numbers of the two components to straddle unity.
Mallegol J, Barry AM, Ciampi E, Glover PM, McDonald PJ, Keddie JL, Wallin M, Motiejauskaite A, Weissenborn PK (2002) Influence of drier combination on through-drying in waterborne alkyd emulsion coatings observed with magnetic resonance profiling, JOURNAL OF COATINGS TECHNOLOGY 74 (933) pp. 113-124 FEDERATION SOC COATING TECH
Simpson TRE, Tabatabaian Z, Jeynes C, Parbhoo B, Keddie JL (2004) Influence of interfaces on the rates of crosslinking in poly(dimethyl siloxane) coatings, JOURNAL OF POLYMER SCIENCE PART A-POLYMER CHEMISTRY 42 (6) pp. 1421-1431 JOHN WILEY & SONS INC
McMurtry S, Wright JD, Jackson DA, Keddie JL (2000) Humidity sensing using PMMA-PMTGA-PMMA polymer in low coherence interferometric system, ELECTRONICS LETTERS 36 (1) pp. 73-74
The isothermal structural relaxation of glassy, spin-cast polymer thin films has been investigated. Specifically, the thickness, h, of freshly-cast poly(methyl methacrylate) thin films was measured over time using spectroscopic ellipsometry. The spin-cast films exhibit a gradual decrease in thickness, which is attributed to structural relaxation of the glass combined with simultaneous solvent loss. In all cases, h was found to be greater than the equilibrium thickness, h0, which is obtained by cooling slowly from the melt. It is observed that both the rate of the volume relaxation and the fractional departure from h0 (referred to as ?o) increase with increasing film thickness. In the limit of very thin films, the initial h is close to h¥, and do is small, whereas in thick films (> 500 nm), a plateau value of ?o of 0.16 is observed, which is close to the volume fraction of the solvent at the vitrification point. This dependence of ?o on thickness is observed regardless of the substrate, polymer molecular weight, or angular velocity during spin-casting. Enhanced mobility near film surfaces could be leading to greater relaxation in thinner films prior to, and immediately after, the vitrification of the polymer during the deposition process.
It is well established that colloidal polymer particles can be used to create organised structures by methods of horizontal deposition, vertical deposition, spin-casting, and surface pattern-assisted deposition. Each particle acts as a building block in the structure. This paper reviews how two-phase (or hybrid) polymer colloids can offer an attractive method to create nanocomposites. Structure in the composite can be controlled at the nanoscale by using such particles. Methods to create armored particles, such as via methods of hetero-flocculation and Pickering polymerization, are of particular interest here. Polymer colloids can also be blended with other types of nanoparticles, e.g. nanotubes and clay platelets, to create nanocomposites. Structure can be controlled over length scales approaching the macroscopic through the assembly of hybrid particles or particle blends via any of the various deposition methods. Colloidal nanocomposites can offer unprecedented long-range 2D or 3D order that provides a periodic modulation of physical properties. They can also be employed as porous templates for further nanomaterial fabrication. Challenges in the design and control of the macroscopic properties, especially mechanical, are considered. The importance of the internal interfacial structure (e.g. between inorganic and polymer particles) is highlighted.
Gorce JP, Bovey D, McDonald PJ, Palasz P, Taylor D, Keddie JL (2002) Vertical water distribution during the drying of polymer films cast from aqueous emulsions., Eur Phys J E Soft Matter 8 (4) pp. 421-429
We present a systematic study of the vertical uniformity of water distribution during the drying of waterborne colloidal films, testing the predictions of a Peclet number Pe defined for this system. Pe indicates the relative contributions of water evaporation and Brownian diffusion in determining the concentration profile in the vertical direction ( i.e. normal to the substrate). When Pe 1, a gradient in the water concentration develops, with less water near the interface with air. The water profiles reveal that the alkyd particles do not coalesce immediately upon contact in close-packing. At later times, a concentrated surface layer develops, but particles are not coalesced in this layer to form a continuous "skin", but rather the structure is likely to be that of a biliquid foam.
Keddie JL, Cory RA, Jones RAL (1998) Polymer dynamics in thin films, MODERN ASPECTS OF COLLOIDAL DISPERSIONS pp. 149-157
Keddie JL, Meredith P, Jones RAL, Donald AM (1996) Film formation of acrylic latices with varying concentrations of non-film-forming latex particles, Langmuir 12 (16) pp. 3793-3801
We have employed ellipsometry and environmental SEM (ESEM) to determine the kinetics of film formation in mixtures of film-forming (FF) and non-film-forming (NFF) acrylic latices. We find that an increasing concentration of NFF latex leads to progressively larger voids. We have also found that minimizing the number of NFF-NFF particle contacts within the mixture results in a denser material. The rate of void closure during the early stages of film formation is enhanced by the presence of NFF latex particles, because the particles lead to a higher surface area that provides a stronger driving force for void closure. Despite this effect, a latex with a higher concentration of NFF particles takes longer to reach full density. We have applied the Mackenzie-Shuttleworth theory to our densification data and found a value for the viscosity of the FF latex that is consistent with the literature. In some cases, we see evidence for polymer viscosity changing with time, indicative of hydroplasticization. We find that our calculated viscosity of the FF latex decreases with increasing temperature and increases with the addition of 40 wt % NFF particles. We comment on the implications that this work has for the measurement of the critical pigment volume concentration.
Polymer colloids are often copolymerized with acrylic acid monomers in order to impart colloidal stability. Here, the effects of the pH on the nanoscale and macroscopic adhesive properties of waterborne poly(butyl acrylate-co-acrylic acid) films are reported. In films cast from acidic colloidal dispersions, hydrogen bonding between carboxylic acid groups dominates the particle-particle interactions, whereas ionic dipolar interactions are dominant in films cast from basic dispersions. Force spectroscopy using an atomic force microscope and macroscale mechanical measurements show that latex films with hydrogen-bonding interactions have lower elastic moduli and are more deformable. They yield higher adhesion energies. On the other hand, in basic latex, ionic dipolar interactions increase the moduli of the dried films. These materials are stiffer and less deformable and, consequently, exhibit lower adhesion energies. The rate of water loss from acidic latex is slower, perhaps because of hydrogen bonding with the water. Therefore, although acid latex offers greater adhesion, there is a limitation in the film formation.
Richardson H, Sferrazza M, Keddie JL (2003) Influence of the glass transition on solvent loss from spin-cast glassy polymer thin films, European Physical Journal E 12 (SUPPL. 1) pp. 75-79
The interdependence of solvent loss and vitrification in spin-cast poly(methyl methacrylate) thin films is explored. Fast measurements of decreases in film thickness, achieved with ellipsometry, indicate that the rate of solvent (toluene) loss decreases sharply when the solvent volume fraction Æsolv falls below about 0.15 and the film vitrifies. Ellipsometry and microgravimetry show that solvent is lost from a glassy thin film (150 nm thick) over of a period of more than ten hours, which is much longer than would be required if it was limited by diffusion in the glass. These results support the recently-proposed idea that the compression of the glass creates an energy barrier that slows down solvent loss. © EDP Sciences / Società Italiana di Fisica / Springer-Verlag 2003.
Nerapusri V, Keddie JL, Vincent B, Bushnak IA (2006) Swelling and deswelling of adsorbed microgel monolayers triggered by changes in temperature, pH, and electrolyte concentration, LANGMUIR 22 (11) pp. 5036-5041 AMER CHEMICAL SOC
LEVINE T, KEDDIE J, REVESZ P, MAYER J, GIANNELIS E (1993) ION-BEAM-INDUCED DENSIFICATION OF ZIRCONIA SOL-GEL THIN-FILMS, JOURNAL OF THE AMERICAN CERAMIC SOCIETY 76 (5) pp. 1369-1379
Variable angle spectroscopic ellipsometry is a nondestructive technique for accurately determining the thicknesses and refractive indices of thin films. Experimentally, the ellipsometry parameters È and are measured, and the sample structure is then determined by one of a variety of approaches, depending on the number of unknown variables. The ellipsometry parameters have been inverted analytically for only a small number of sample types. More general cases require either a model-based numerical technique or a series of approximations combined with a sound knowledge of the test sample structure. In this paper, the combinatorial optimization technique of simulated annealing is used to perform least-squares fits of ellipsometry data (both simulated and experimental) from both a single layer and a bilayer on a semi-infinite substrate using what is effectively a model-free system, in which the thickness and refractive indices of each layer are unknown. The ambiguity inherent in the best-fit solutions is then assessed using Bayesian inference. This is the only way to consistently treat experimental uncertainties along with prior knowledge. The Markov chain Monte Carlo algorithm is used. Mean values of unknown parameters and standard deviations are determined for each and every solution. Rutherford backscattering spectrometry is used to assess the accuracy of the solutions determined by these techniques. With our computer analysis of ellipsometry data, we find all possible models that adequately describe that data. We show that a bilayer consisting of a thin film of poly(styrene) on a thin film of silicon dioxide on a silicon substrate results in data that are ambiguous; there is more than one acceptable description of the sample that will result in the same experimental data.
Polymer coatings with periodic topographic patterns, repeating over millimetre length scales, can be created from lateral flows in an aqueous dispersion of colloidal particles. The flow is driven by differences in evaporation rate across the wet film surface created by IR radiative heating through a shadow mask. This new process, which we call IR radiation-assisted evaporative lithography (IRAEL), combines IR particle sintering with the concept of evaporative lithography. Here, a series of experiments has been conducted in which the mass of the latex is measured as a function of the exposure time under infrared radiation through a mask. The water evaporation rates and the minimum exposure time required for a dry film are estimated as a function of the power density of the IR emitter. The temperature of the wet film is monitored to avoid overheating and boiling of the water, which will otherwise cause defects. It is demonstrated that textured films can be created on a variety of substrates (plastics, metals, paper and glass), and processing times can be as short as 5 min. We use IRAEL to decorate household goods with an aesthetic coating with the desired texture. © 2013 Elsevier B.V. All rights reserved.
KEDDIE J, NORTON L, KRAMER E, GIANNELIS E (1993) NEUTRON REFLECTOMETRY CHARACTERIZATION OF INTERFACE WIDTH BETWEEN SOL-GEL TITANIUM-DIOXIDE AND SILICON DIOXIDE THIN-FILMS, JOURNAL OF THE AMERICAN CERAMIC SOCIETY 76 (10) pp. 2534-2538
Keddie JL, Jones RAL (1995) Depression of the glass transition temperature in ultra-thin, grafted polystyrene films, Materials Research Society Symposium - Proceedings 366 pp. 183-188
We have used ellipsometry to measure the glass transition temperature (Tg) of ultra-thin films of polystyrene (PS) (less than 10 nm thick) obtained by grafting PS-COOH on the native oxide of Si. We find that Tg in these ultra-thin films is depressed from the bulk value by as much as 35 K. This is in qualitative accord with our earlier results on thicker non-grafted films of PS.
Agirre A, de las Heras-Alarcon C, Wang T, Keddie JL, Asua JM (2010) Waterborne, Semicrystalline, Pressure-Sensitive Adhesives with Temperature-Responsiveness and Optimum Properties, ACS APPLIED MATERIALS & INTERFACES 2 (2) pp. 443-451 AMER CHEMICAL SOC
Tzitzinou A, Keddie JL, Jeynes C, Mulder M, Geurts J, Treacher KE, Satguru R, Zhdan P (1999) Molecular weight effects on film formation of latex and surfactant morphology., ABSTRACTS OF PAPERS OF THE AMERICAN CHEMICAL SOCIETY 218 pp. U609-U609 AMER CHEMICAL SOC
We highlight the significance of capillary pressure in the directed assembly of nanorods in ordered arrays of colloidal particles. Specifically, we discuss mechanisms for the assembly of carbon nanotubes at the interstitial sites between latex polymer particles during composite film formation. Our study points to general design rules to be considered to optimize the ordering of nanostructures within such polymer matrices. In particular, gaining an understanding of the role of capillary forces is critical. Using a combination of electron microscopy and atomic force microscopy, we show that the capillary forces acting on the latex particles during the drying process are sufficient to bend carbon nanotubes. The extent of bending depends on the flexural rigidity of the carbon nanotubes and whether or not they are present as bundled ensembles. We also show that in order to achieve long-range ordering of the nanotubes templated by the polymer matrix, it is necessary for the polymer to be sufficiently mobile to ensure that the nanotubes are frozen into the ordered network when the film is formed and the capillary forces are no longer dominant. In our system, the polymer is plasticized by the addition of surfactant, so that it is sufficiently mobile at room temperature. Interestingly, the carbon nanotubes effectively act as localized pressure sensors, and as such, the study agrees well with previous theoretical predictions calculating the magnitude of capillary forces during latex film formation.
Daniloska V, Keddie JL, Asua JM, Tomovska R (2014) MoS2 nanoplatelet fillers for enhancement of the properties of waterborne pressure-sensitive adhesives, ACS Applied Materials and Interfaces 6 (24) pp. 22640-22648
© 2014 American Chemical Society.Nanocomposite pressure-sensitive adhesives (PSAs) composed of polyurethane (PU)/(meth)acrylates reinforced with MoS2 nanoplatelets were prepared by blending aqueous dispersions. MoS2 crystals were exfoliated by sonication in water in the presence of poly(vinylpyrrolidone) (PVP, molecular weight of 10 000 g mol-1) to prepare an aqueous dispersion. Waterborne colloidal polymer particles (latex) were synthesized by miniemulsion photopolymerization in a continuous tubular reactor. The adhesive and mechanical properties from the resulting nanocomposite films were determined as the MoS2 fraction was increased. A superior balance of viscoelastic properties was achieved with 0.25 wt % loading of the MoS2 nanoplatelets, leading to a tack adhesion energy that was three times greater than that for the original PSA.
Existing inorganic materials for radiation sensors suffer from several drawbacks, including their inability to cover large curved areas, lack of tissue equivalence toxicity, and mechanical inflexibility. As an alternative to inorganics, poly(triarylamine) (PTAA) diodes have been evaluated for their suitability for detecting radiation via the direct creation of X-ray induced photocurrents. A single layer of PTAA is deposited on indium tin oxide (ITO) substrates, with top electrodes selected from Al, Au, Ni, and Pd. The choice of metal electrode has a pronounced effect on the performance of the device; there is a direct correlation between the diode rectification factor and the metal-PTAA barrier height. A diode with an Al contact shows the highest quality of rectifying junction, and it produces a high X-ray photocurrent (several nA) that is stable during continuous exposure to 50 kV Mo K alpha X-radiation over long time scales, combined with a high signal-to-noise ratio with fast response times of less than 0.25 s. Diodes with a low band gap, 'Ohmic' contact, such as ITO/PTAA/Au, show a slow transient response. This result can be explained by the build-up of space charge at the metal-PTAA interface, caused by a high level of charge injection due to X-ray-induced carriers. These data provide new insights into the optimum selection of metals for Schottky contacts on organic materials, with wider applications in light sensors and photovoltaic devices.
Udagama R, Bourgeat-Lami E, Mckenna TFL, Alarcón CDLH, Keddie JL, Tsavalas JG (2014) Acrylic-alkyd hybrids: Secondary nucleation, particle morphology, and limiting conversions, Macromolecular Reaction Engineering
The chemical incorporation of an unsaturated alkyd into an acrylic polymer created via miniemulsion polymerisation was studied. The variation of the number ratio of polymer particles to initial droplets with conversion, and changes in individual monomer conversions with increasing alkyd levels were the main quantities used to study the effect of increasing alkyd quantity in the hybrid system. Homogeneous nucleation was more significant in systems rich in the more hydrophilic methyl methacrylate (MMA). Changes in particle morphology with monomer conversion, as well as limited monomer conversion were observed. The results emphasize the importance of proper pairing of the miscibility between the specific acrylics and alkyds used in these hybrid polymers. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
KEDDIE J, JONES R, CORY R (1994) INTERFACE AND SURFACE EFFECTS ON THE GLASS-TRANSITION TEMPERATURE IN THIN POLYMER-FILMS, FARADAY DISCUSSIONS 98 pp. 219-230
Deplace F, Rabjohns MA, Yamaguchi T, Foster AB, Carelli C, Lei C-H, Ouzineb K, Keddie JL, Lovell PA, Creton C (2009) Deformation and adhesion of a periodic soft-soft nanocomposite designed with structured polymer colloid particles, SOFT MATTER 5 (7) pp. 1440-1447
ROYAL SOC CHEMISTRY
Gundabala VR, Lei C-H, Ouzineb K, Dupont O, Keddie JL, Routh AF (2008) Lateral surface nonuniformities in drying latex films, AIChE Journal 54 (12) pp. 3092-3105 Wiley
The length scales of film, thickness nonuniformities, commonly observed in polymer colloid (i.e., latex) films, are predicted. This prediction is achieved by investigating the stability behavior of drying latex films. A linear stability analysis is performed on a base solution representing a uniformly drying latex film containing a surfactant. The analysis identifies film thickness nonuniformities over two length scales: long (millimeter) range (from lubrication theory) and short (micrometer) range (from nonlubrication theory). Evaporation and surfactant desorption into the bulk film are identified as the primary destabilizing mechanisms during drying. Experimental evidence through direct visualization and atomic force microscopy confirm the existence of nonuniformities over both length scales, which are shown to be functions of parameters such as initial particle volume fraction, surfactant amount, and desorption strength, while being independent of drying rate. © 2008 American Institute of Chemical Engineers.
Daar E, Woods E, Keddie JL, Nisbet A, Bradley DA (2010) Effect of penetrating ionising radiation on the mechanical properties of pericardium, NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION A-ACCELERATORS SPECTROMETERS DETECTORS AND ASSOCIATED EQUIPMENT 619 (1-3) pp. 356-360 ELSEVIER SCIENCE BV
Andrei DC, Hay JN, Keddie JL, Sear RP, Yeates SG (2000) Surface levelling of thermosetting powder coatings: theory and experiment, Journal of Physics D: Applied Physics 33 (16) pp. 1975-1981
The deposition of protective coatings from thermosetting polymer powders is an ecological, economic and energy-efficient technology. A frequent problem encountered with powder coatings is a rough surface (with undulations on a length scale much greater than the powder particle size) that detracts from the visual appearance. The levelling (i.e. flattening) of the surface of a polymer melt is driven by the minimization of the surface energy but opposed by the (possibly time-dependent) viscosity of the melt. We address the problem by developing a model of surface levelling to consider flow in two directions, building upon a one-dimensional model already in the literature. We have performed simulations to predict the final coating profiles starting with a Gaussian profile and using experimentally determined values of polymer viscosity. To compare to the simulations, we have measured experimentally the dimensions of surface undulations on coatings formed from thermosetting acrylic powder layers having purposely created features of known dimensions. There is good agreement between simulation and experiment. Both find that the levelling proceeds to a greater extent with increasing coating thickness and with decreasing lateral dimension of the surface undulation. Our results open up the possibility of predicting final surface topography given the rheological properties of a polymer.
KEDDIE J, MEREDITH P, JONES R, DONALD A (1995) RATE-LIMITING STEPS IN THE FILM FORMATION OF WATER-BORNE ACRYLIC LATTICES AS ELUCIDATED WITH ELLIPSOMETRY AND ENVIRONMENTAL-SEM, ABSTRACTS OF PAPERS OF THE AMERICAN CHEMICAL SOCIETY 210 pp. 76-PSME
Tzitzinou A, Keddie JL, Geurts JL, Mulder M, Satguru R, Treacher KE (2001) Molecular weight effects on the film formation of latex and on surfactant distribution and morphology, ACS Symposium Series 790 pp. 58-87
It is well known that viscosity, self-diffusion coefficient and glass transition temperature are a strong function of molecular weight (MW). Here we report the film formation characteristics of an acrylic (BMA/MMA/MAA) latex as a function of its average MW, considering four molecular weights ranging from 7,500 to 705,000 Daltons. As a means of taking into account the lower glass transition temperature and viscosity expected in the lower MW latices, we compare the film formation behaviours at the same temperature increment above their respective minimum film formation temperatures (MFT). We find that the lower MW latices form a film with a lower void concentration and lower surface roughness in comparison to the higher MW latices at the same temperature relative to the MFT. Non-invasive analysis of the film formation using ellipsometry finds evidence for void formation in the high MW latex (Mw = 705, 000 Daltons) up to 30°C above MFT. In contrast, the lowest MW latex (Mw = 7,500 Daltons) forms a dense film with few, if any, voids immediately upon the evaporation of water and at temperatures as low as 5°C above MFT. These differences can be partly attributed to varying degrees of plasticization by water. In addition, the film morphology at the polymer/air interface was investigated using atomic force microscopy. Surface features were attributed to the presence of surfactant. A low MW latex shows surfactant features at a lower film formation temperature (relative to the MFT) and/or a shorter film-formation time in comparison to the high MW latex.
Salamanca JM, Ciampi E, Faux DA, Glover PM, McDonald PJ, Routh AF, Peters ACIA, Satguru R, Keddie JL (2001) Lateral drying in thick films of waterborne colloidal particles, LANGMUIR 17 (11) pp. 3202-3207 AMER CHEMICAL SOC
Jurewicz I, King AAK, Worajittiphon P, Asanithi P, Brunner EW, Sear RP, Hosea TJC, Keddie JL, Dalton AB (2010) Colloid-Assisted Self-Assembly of Robust, Three-Dimensional Networks of Carbon Nanotubes over Large Areas, MACROMOLECULAR RAPID COMMUNICATIONS 31 (7) pp. 609-615 WILEY-V C H VERLAG GMBH
Keddie JL (2001) Structural analysis of organic interfacial layers by ellipsometry, Current Opinion in Colloid and Interface Science 6 (2) pp. 102-110
Ellipsometry has 'come of age' as a technique for the analysis of problems related to colloid and interface science. It has advanced far beyond applications of measuring film thickness or optical constants - although these remain important uses. Studies of the structure of polymers at the solid/liquid interface have been advanced significantly by the realisation of Fourier transform ellipsometry. Another important achievement has been the calibrated measurement of the dynamic surface excess at the flowing surface of a liquid jet. The users of ellipsometry to study critical adsorption in binary liquids and to measure the width of liquid/liquid interfaces are also noteworthy. An important development is the use of infrared - rather than visible - light, which opens up numerous possibilities for the simultaneous structural and chemical interrogation of interfaces non-invasively. © 2001 Elsevier Science Ltd. All rights reserved.
Akram N, Ishaq M, Zuber M, Gurney RS, Keddie JL (2013) Influence of Polyol Molecular Weight and Type on the Tack and Peel Properties of Waterborne Polyurethane Pressure-Sensitive Adhesives, Macromolecular Reaction Engineering 7 (10) pp. 493-503
A requirement for optimum performance in a pressure-sensitive adhesive (PSA) is the right balance between viscous and elastic properties, achieved by controlling the molecular architecture. Here, waterborne polyurethane PSAs are synthesized using a blend of polyether and polyalkene-based polyols. The effects of the polyol type and molecular weight on the adhesive and thermomechanical properties are explored to optimize them for PSA applications. A linear polyurethane is synthesized by the reaction of an aliphatic diisocyanate with a diol blend of polypropylene glycol (PPG) and hydroxyl-terminated polybutadiene (HTPB). With increasing concentrations of flexible HTPB segments and the associated increased viscous dissipation a favorable increase in the tack adhesion energy and peel strength is obtained. Adhesive properties are improved with increasing PPG molecular weight because chain entanglements become possible in the soft segments and raise the storage modulus. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
Keddie JL, Meredith P, Jones RAL, Donald AM (1996) Rate-Limiting Steps in Film Formation of Acrylic Latices as Elucidated with Ellipsometry and Environmental Scanning Electron Microscopy, ACS Symposium Series 648 pp. 332-348
Our data indicate that evaporation is the rate-limiting step in film formation when the temperature of a latex is about 20 K or more above its glass transition temperature (Tg). When a latex is nearer to its Tg, the rate-limiting step in film formation is deformation of the latex particles, possibly by viscous flow of the polymer driven by the reduction in surface energy. In this latter case, there is evidence that a drying front first creates air voids. Subsequently, a coalescence front moves inward from the periphery in the plane of the film. Evaporation rates are retarded in a latex that is well-above its Tg, probably as a result of the reduced surface area of water, caused by extensive particle deformation. We studied the kinetics of film formation in an acrylic latex using ellipsometry and environmental-SEM, techniques which allow in situ observation of wet and partially-wet latices. We fit our data to a model describing the coalescence of voids by viscous flow.
Mallegol J, Keddie JL, Dupont O (2001) New insights into the imaging of waterborne acrylic pressure-sensitive adhesives by tapping mode AFM., ABSTRACTS OF PAPERS OF THE AMERICAN CHEMICAL SOCIETY 222 pp. U346-U346
Andrei DC, Keddie JL, Hay JN, Yeates SG, Briscoe BJ, Parsonage D (2001) Nano-mechanical properties and topography of thermosetting acrylic powder coatings, JOURNAL OF COATINGS TECHNOLOGY 73 (912) pp. 65-73
Keddie JL, Utgenannt A, Kanaras AG, Muskens OL (2013) Directed organization of gold nanoparticles in polymer coatings over large length scales through infrared-assisted evaporative lithography, ABSTRACTS OF PAPERS OF THE AMERICAN CHEMICAL SOCIETY 245 AMER CHEMICAL SOC
Worajittiphon P, Jurewicz I, King AAK, Keddie JL, Dalton AB (2010) Enhanced Thermal Actuation in Thin Polymer Films Through Particle Nano-Squeezing by Carbon Nanotube Belts, ADVANCED MATERIALS 22 (46) pp. 5310-5314 WILEY-V C H VERLAG GMBH
Adikaari AADT, Carey JD, Stolojan V, Keddie JL, Silva SRP (2006) Bandgap enhancement of layered nanocrystalline silicon from excimer laser crystallization, NANOTECHNOLOGY 17 (21) pp. 5412-5416 IOP PUBLISHING LTD
Aramendia E, Mallegol J, Jeynes C, Barandiaran MJ, Keddie JL, Asua JM (2003) Distribution of surfactants near acrylic latex film surfaces: A comparison of conventional and reactive surfactants (surfmers), LANGMUIR 19 (8) pp. 3212-3221 AMER CHEMICAL SOC
There is a need to know the nanostructure of pressure-sensitive adhesive (PSA) films obtained from waterborne polymer colloids so that it can be correlated with properties. Intermittent-contact atomic force microscopy (AFM) of an acrylic waterborne PSA film identifies two components, which can be attributed to the polymer and the solids in the serum (mainly surfactant). It is found that when the average AFM tapping force, Fav, is relatively low, the polymer particles appear to be concave. But when Fav is higher, the particles appear to have a convex shape. This observation is explained by a height artefact caused by differences in the indentation depths into the two components that vary with the tapping amplitude and Fav. To achieve the maximum contrast between the polymer and serum components, Fav should be set such that the indentation depths are as different as possible. Unlike what is found for the height images, the phase contrast images of the PSA do not show a reversal in contrast over the range of tapping conditions applied. The phase images are thus reliable in distinguishing the two components of the PSA according to their viscoelastic properties. At the surface of films dried at room temperature, the serum component is found in localized regions within permanent depression into the film. © 2006 Elsevier Inc. All rights reserved.
Newling B, Glover PM, Keddie JL, Lane DM, McDonald PJ (1997) Concentration profiles in creaming oil-in-water emulsion layers determined with stray field magnetic resonance imaging, Langmuir 13 (14) pp. 3621-3626
We report the first use of stray field magnetic resonance imaging in the determination of concentration profiles in layers (with submillimeter thickness) of coarse oil-in-water emulsions that are undergoing creaming. We compare our results for emulsions having various oil contents to the predictions of a numerical model. In emulsions having low oil content (12 and 23 vol %), we find that the model adequately predicts the profile shape and time-dependent change in the lower region of the emulsion. In the cream layer at the top of each of the samples, however, the predictions of the model deviate substantially from the observed profiles. Whereas the model assumes that the concentration of oil in the cream layer is constant as the layer increases in thickness, we observe that there is a concentration gradient in the cream layer and that the concentration of oil in the layer increases with time. In explaining our findings, we consider the effects of polydispersity and the presence of gum xanthan in the continuous phase and also the possibility of gradual compaction of oil droplets in the cream layer (a phenomenon not considered in the model).
Keddie JL, Giannelis EP (1990) Ion-beam analysis of silica sol-gel films. Structural and compositional evolution, Journal of the American Ceramic Society 73 (10) pp. 3106-3109
Rutherford backscattering and forward recoil spectrometry have been used to determine the chemical composition and density of SiO2 sol-gel films. The as-deposited films are relatively dense, because of considerable interpenetration of weakly branched silicate precursors, while they contain significant amounts of hydroxyl groups in their structure. Annealing in flowing Ar increases the density of the films with values approaching that of amorphous silica at temperatures as low as 450°C but it fails to completely remove all the hydroxyl groups from the structure.
The adhesion of Staphylococcus epidermidis, Escherichia coli, and Candida albicans on mucin coatings was evaluated to explore the feasibility of using the coating to increase the infection resistance of biomaterials. Coatings of bovine submaxillary mucin (BSM) were deposited on a base layer consisting of a poly(acrylic acid-b-methyl methacrylate) (PAA-b-PMMA) diblock copolymer. This bi-layer system exploits the mucoadhesive interactions of the PAA block to aid the adhesion of mucin to the substratum, whereas the PMMA block prevents dissolution of the coating in aqueous environments. The thickness of the mucin coating was adjusted by varying the pH of the solution from which it was deposited. Thin mucin coatings decreased the numbers of bacteria but increased the numbers of C. albicans adhering to the copolymer and control surfaces. Increasing the mucin film thickness resulted in a further lowering of the density of adhering S. epidermidis cells, but it did not affect the density of E. coli. In contrast, the density of C. albicans increased with an increase in mucin thickness.
KEDDIE J, LI J, MAYER J, GIANNELIS E (1991) EFFECT OF NITRIDATION RATE ON THE COMPOSITION AND CONDUCTIVITY OF TITANIUM NITRIDE FILMS PREPARED FROM SOL-GEL TITANIA, JOURNAL OF THE AMERICAN CERAMIC SOCIETY 74 (11) pp. 2937-2940
Gilchrist VA, Lu JR, Keddie JL, Staples E, Garrett P (2000) Adsorption of penta(ethylene glycol) monododecyl ether at the solid poly(methyl methacrylate)-water interface: A spectroscopic ellipsometry study, Langmuir 16 (2) pp. 740-748
We have examined the adsorption of a nonionic surfactant, penta(ethylene glycol) monododecyl ether (C12E5), at the poly(methyl methacrylate) (PMMA)-water interface using spectroscopic ellipsometry. The solid PMMA surface was deposited by spin casting an ultrathin film onto a freshly cleaned silicon wafer. Measurements by both spectroscopic ellipsometry (SE) and atomic force microscopy (AFM) showed that the thin PMMA film was uniform with no prominent structural features on the surface. The adsorption of C12E5 at the solid PMMA-aqueous solution interface was studied using a specially designed cell with a fixed angle of incidence of 75°, and the measurements were made over a wide concentration range around the critical micellar concentration (cmc). It was found that the adsorption is completely reversible and that there is no observable penetration of C12E5 into the PMMA. The adsorption was found to reach equilibrium well within seconds. Although spectroscopic ellipsometry cannot allow a reliable measurement of layer thickness as a result of coupling between refractive indices and layer thickness for ultrathin layers, the surface excess at a given concentration can be determined reliably. The limiting area per molecule at the cmc was calculated to be 50±3 angstroms2, in good agreement with the value obtained from a previous neutron reflection study.
Chen WL, Shull KR, Papatheodorou T, Styrkas DA, Keddie JL (1999) Equilibrium swelling of hydrophilic polyacrylates in humid environments, Macromolecules 32 (1) pp. 136-144
The hydrophilicity of polymers, as indicated by their swelling characteristics in water, is an important parameter with regard to their use as coatings which are able to modify the wettability and adhesive properties of a material. We have investigated the swelling behavior of a series of hydrophilic random copolymer coatings in controlled humidity environments and in water. Swelling data were obtained from a quartz crystal microbalance (QCM) and from spectroscopic ellipsometry. The hydrophilic polymers are based on polyacrylates with low molecular weight side chains of poly(ethylene glycol) (PEG). These polymers also contain a random distribution of acrylic acid. Triblock copolymers with these random copolymers as the midblock and poly(methyl methacrylate) (PMMA) as the end blocks have also been investigated. At low and intermediate humidities, the swelling behavior of appropriately chosen block copolymers is similar to the swelling behavior of the corresponding polymers that do not have the PMMA end blocks. Substantial differences between the two types of polymers are observed at very high humidities and in water. The PMMA end blocks stabilize the structure of the copolymer layer so that it does not dissolve in water. Swelling curves obtained from the quartz crystal microbalance and from ellipsometry are in agreement with one another when the shape of the quartz crystal resonance (as determined by impedance spectroscopy) is not affected by humidity. We also find evidence for a reversible, humidity-induced phase transition which is readily detectable by the quartz crystal microbalance. © 1999 American Chemical Society.
Reiter has recently reported a situation in which the dewetting of quasi-solid films is linked to plastic deformation--rather than viscous flow--resulting from capillary forces. Herein we propose that, in thin films of some glassy polymers--especially poly(methyl methacrylate) (PMMA)--prepared by spin-casting from solvent, structural relaxation might impart sufficient stress to cause plastic deformation. We find that PMMA films decrease in thickness by several percent, which is sufficient to create significant stress in those cases in which the film is attached to a rigid substrate. The floating technique, which can take tens of minutes, might allow most of the structural relaxation to occur prior to dewetting experiments.
KEDDIE J, GIANNELIS E (1991) EFFECT OF HEATING RATE ON THE SINTERING OF TITANIUM-DIOXIDE THIN-FILMS - COMPETITION BETWEEN DENSIFICATION AND CRYSTALLIZATION, JOURNAL OF THE AMERICAN CERAMIC SOCIETY 74 (10) pp. 2669-2671
Simpson TRE, Keddie JL, Parbhoo B (2003) Influence of interfaces on the rate of crosslinking in silicone coatings., ABSTRACTS OF PAPERS OF THE AMERICAN CHEMICAL SOCIETY 225 pp. U710-U710
Jenneson PM, Clough AS, Keddie JL, Lu JR, Meredith P (1997) Non-ionic surfactant concentration profiles in undamaged and damaged hair fibres determined by scanning ion beam nuclear reaction analysis, Nuclear Instruments and Methods in Physics Research, Section B: Beam Interactions with Materials and Atoms 132 (4) pp. 697-703
Nuclear Reaction Analysis (NRA) was used with a scanning MeV 3He ion microbeam to determine the extent of permeation and segregation of a deuterated non-ionic surfactant (dC12E5) into virgin (undamaged) and alkalinic perm damaged hair fibres. 2-D concentration maps show an accumulation of deuterated surfactant in the cortex and medulla of both the virgin and damaged hair. By normalising to the matrix carbon, surfactant levels in the damaged hair were found to be three times higher than in the undamaged hair. This is the first reported direct spatial evidence of the penetration of surfactant into the centre of hair fibres. Furthermore it is the first application of NRA to this type of complex biological matrix. © 1997 Elsevier Science B.V.
Ciampi E, Goerke U, Keddie JL, McDonald PJ (2000) Lateral transport of water during drying of alkyd emulsions, LANGMUIR 16 (3) pp. 1057-1065 AMER CHEMICAL SOC
López García I, Keddie JL, Sferrazza M (2011) Probing the early stages of solvent evaporation and relaxation in solvent-cast polymer thin films by spectroscopic ellipsometry, Surface and Interface Analysis 43 (11) pp. 1448-1452 Wiley
The formation of solvent-cast, poly(methyl methacrylate) (PMMA) thin films from dilute bromobenzene solutions was studied
using an ellipsometry technique. Bromobenzene has a relatively high refractive index (compared to PMMA), which provides
contrast in ellipsometry, allowing the concentration to be determined. The solvent also has a relatively low evaporation rate,
which makes the film formation slow enough to capture via the technique. The formation of the glassy film is thus studied
in situ, and information on solvent and void concentration in the thin film during the film formation process is obtained. There is
evidence that nanovoids (representing intramolecular space) develop in the film when solvent evaporates.
Wang T, Lei CH, Dalton AB, Creton C, Lin Y, Fernando KAS, Sun YP, Manea M, Asua JM, Keddie JL (2006) Waterborne, nanocomposite pressure-sensitive adhesives with high tack energy, optical transparency, and electrical conductivity, Advanced Materials 18 (20) pp. 2730-2734
The waterborne, nanocomposite pressure-sensitive adhesives (PSA) with high tack energy, optical transparency, and electrical conductivity was studied. Pressure-sensitive adhesives adhere instantly and firmly to nearly any surface under the application of light pressure, without covalent bonding and activation. The debonding of PSAs occurs by a cavitation process followed by cavity expansion to create fibrils that extend in traction and contribute to the energy of adhesion. The surfactants and water-soluble polymers in latex films are known to decrease adhesive performance. It has been recognized that the interfaces in polymer/ carbon nanotubes (CNT) nanocomposites can have an influence on the viscoelastic property of the PSAs. Electrical conductivity in PSAs is conventionallky achieved through the use of metallic fillers in the form of flakes and particles.
The coating of substrates with an extracellular matrix (ECM) protein, such as fibronectin (FN), is often employed to increase cell adhesion and growth. Here, we examine the influence of the size scale and geometry of novel FN nanopatterns on the adhesion and spreading of Chinese Hamster Ovary (CHO) cells. The FN is patterned on the surface of templates created through the self-assembly of polystyrene-block-polyisoprene (PS-b-PI) diblock copolymers. Both ring-like and stripe-like FN nanopatterns are created through the preferential adsorption of FN on PS blocks, as confirmed through the complementary use of atomic force microscopy and secondary ion mass spectrometry. The ring-like FN nanopattern substrate increases the cells' adhesion compared with the cells on homogeneous FN surfaces and the stripe-like FN nanopatterns. Cell adhesion is high when the FN ring size is greater than 50 nm and when the surface coverage of FN is less than ca. 85%. We suggest that the ring-like nanopatterns of FN may be aiding cell adhesion by increasing the clustering of the proteins (integrins) with which cells bind to the nanopatterned substrate. This clustering is required for cell adhesion. In comparison to lithographic techniques, the FN templating method, presented here, provides a simple, convenient and economical way of coating substrates for tissue cultures and should be applicable to tissue engineering.
Semiconducting polymers have previously been used as the transduction material in x-ray dosimeters, but these devices have a rather low detection sensitivity because of the low x-ray attenuation efficiency of the organic active layer. Here, we demonstrate a way to overcome this limitation through the introduction of high density nanoparticles having a high atomic number (Z) to increase the x-ray attenuation. Specifically, bismuth oxide (Bi
) nanoparticles (Z=83 for Bi) are added to a poly(triarylamine) (PTAA) semiconducting polymer in the active layer of an x-ray detector. Scanning electron microscopy (SEM) reveals that the Bi
nanoparticles are reasonably distributed in the PTAA active layer. The reverse bias dc currentvoltage characteristics for PTAABi
diodes (with indium tin oxide (ITO) and Al contacts) have similar leakage currents to ITO/PTAA/Al diodes. Upon irradiation with 17.5keV x-ray beams, a PTAA device containing 60wt% Bi
nanoparticles demonstrates a sensitivity increase of approximately 2.5 times compared to the plain PTAA sensor. These results indicate that the addition of high-Z nanoparticles improves the performance of the dosimeters by increasing the x-ray stopping power of the active volume of the diode. Because the Bi
has a high density, it can be used very efficiently, achieving a high weight fraction with a low volume fraction of nanoparticles. The mechanical flexibility of the polymer is not sacrificed when the inorganic nanoparticles are incorporated. © 2012 IOP Publishing Ltd.
Selvakumaran J, Keddie JL, Ewins DJ, Hughes MP (2008) Protein adsorption on materials for recording sites on implantable microelectrodes, JOURNAL OF MATERIALS SCIENCE-MATERIALS IN MEDICINE 19 (1) pp. 143-151 SPRINGER
Tzitzinou A, Keddie JL, Geurts JM, Peters ACIA, Satguru R (2000) Film formation of latex blends with bimodal particle size distributions: Consideration of particle deformability and continuity of the dispersed phase, Macromolecules 33 (7) pp. 2695-2708
The film formation of dispersions with bimodal particle size distribution and with varying concentrations of the two particle sizes are studied. The formation of deformable blends with soft particles is compared with those of deformable blends with nondeformable particles. Ellipsometry is used to acquire data for studying film morphology.
Templated surfaces can be used to create patterns of proteins for applications in cell biology, biosensors, and tissue engineering. A diblock copolymer template, which contains a pair of hydrophobic blocks, has been developed. The template is created from well-ordered, nonequilibrium surface structures of poly(styrene-b-isoprene) (PS-b-PI) diblock copolymers, which are achieved in ultrathin films having a thickness of less than one domain period. Adsorption and nanopatterning of bovine serum albumin (BSA) on these thin films were studied. After incubation of the copolymer templates in BSA solutions (500 ¼g/mL) for a period of 1 h, BSA molecules formed either a striped or a dense, ringlike structure, closely resembling the underlying polymer templates. In this ?hard-soft? PS-b-PI system, BSA molecules were preferentially adsorbed on the hard PS domains, rather than on the soft PI domains. Secondary ion mass spectroscopy (SIMS) and contact angle analysis revealed that, with more PI localized at the free surface, fewer BSA molecules were adsorbed. SIMS analysis confirmed that BSA molecules were adsorbed selectively on the PS blocks. This is the first example of two hydrophobic blocks of a diblock copolymer being used as a protein patterning template. Previously reported diblock copolymer templates used hydrophilic and hydrophobic pairs. A potentially useful characteristic of this template is that it is effective at high protein solution concentrations (up to 1 mg/mL) and for long incubation times (up to 2 h), which broadens its range of applicability in various uses.
The loss of optical transparency when polymer films are immersed in water, which is called ?water whitening,? severely limits their use as clear barrier coatings. It is found that this problem is particularly acute in films deposited from polymers synthesized via emulsion polymerization using surfactants. Water whitening is less severe in secondary dispersion polymers, which are made by dispersing solution polymers in water without the use of surfactants. NMR relaxometry in combination with optical transmission analysis and electron microscopy reveal that some of the water sorbed in emulsion polymer films is contained within nano-sized ?pockets? or bubbles that scatter light. In contrast, the water in secondary dispersion polymer films is mainly confined at particle interfaces, where it scatters light less strongly and its molecular mobility is reduced. The addition of surfactant to a secondary dispersion creates a periodic structure that displays a stop band in the optical transmission. The total amount of sorbed water is not a good indicator of polymers prone to water whitening. Instead, the particular locations of the water within the film must be considered. Both the amount of water and the size of the local water regions (as are probed by NMR relaxometry) are found to determine water whitening.
Keddie JL, Andrei DC, Sear RPL, Yeates SG (1999) Surface flattening of thermosetting powder coatings: Theory and experiment., ABSTRACTS OF PAPERS OF THE AMERICAN CHEMICAL SOCIETY 218 pp. U626-U626 AMER CHEMICAL SOC
Utgenannt A, Muskens OL, Kanaras AG, Keddie JL (2013) Directed organization of gold nanoparticles in polymer coatings through infrared-assisted evaporative lithography, Chemical Communications 49 (39) pp. 4253-4255
Infrared-assisted evaporative lithography (IRAEL) is presented as an emerging technology to direct the assembly of gold nanospheres (AuNSs) into large-scale superstructures within colloidal polymeric coatings. The organization of gold nanoparticle arrays within the superstructures can be tuned over length scales, ranging from micrometers up to several millimetres, giving rise to intrinsic plasmonic properties. © 2013 The Royal Society of Chemistry.
Semiconducting polymer X-radiation detectors are a completely new family of low-cost radiation detectors with potential application as beam monitors or dosimeters. These detectors are easy to process, mechanically flexible, relatively inexpensive, and able to cover large areas. However, their x-ray photocurrents are typically low as, being composed of elements of low atomic number (Z), they attenuate x-rays weakly. Here, the addition of high-Z nanoparticles is used to increase the x-ray attenuation without sacrificing the attractive properties of the host polymer. Two types of nanoparticles (NPs) are compared: metallic tantalum and electrically insulating bismuth oxide. The detection sensitivity of 5 µm thick semiconducting poly([9,9-dioctylfluorenyl-2,7-diyl]-co-bithiophene) diodes containing tantalum NPs is four times greater than that for the analogous NP-free devices; it is approximately double that of diodes containing an equal volume of bismuth oxide NPs. The x-ray induced photocurrent output of the diodes increases with an increased concentration of NPs. However, contrary to the results of theoretical x-ray attenuation calculations, the experimental current output is higher for the lower-Z tantalum diodes than the bismuth oxide diodes, at the same concentration of NP loading. This result is likely due to the higher tantalum NP electrical conductivity, which increases charge transport through the semiconducting polymer, leading to increased diode conductivity.
Wang T, Lei C-H, Dalton AB, Manea M, Asua JM, Keddie JL (2007) COLL 306-Waterborne nanocomposite pressure-sensitive adhesives: Achieving enhanced adhesion combined with electrical conductivity, ABSTRACTS OF PAPERS OF THE AMERICAN CHEMICAL SOCIETY 233 AMER CHEMICAL SOC
Lei C-H, Ouzineb K, Dupont O, Routh AF, Gundabala VR, Hinder SJ, Keddie JL (2007) Lateral distribution of surfactants in waterborne pressure sensitive adhesive films: Theory and experiment, ABSTRACTS OF PAPERS OF THE AMERICAN CHEMICAL SOCIETY 233 AMER CHEMICAL SOC
Previous theoretical and experimental work has shown that surface tension gradients in
liquid layers create surface defects and inhibit the levelling of an uneven surface. In coatings
deposited from thermosetting polyester powders, which are studied here, small amounts
of a low molecular-weight acrylate are incorporated to act as a ?flow agent.? We find that
this additive lowers the surface tension of the polymer melt and has a minor effect on the
melt viscosity. A slower rate of levelling results from the decreased surface tension. We
provide experimental evidence that lateral gradients in the surface tension of the polymer
melt, resulting from the non-uniform distribution of the flow agent, inhibit the levelling of
the surface. Specifically, the surface roughness of a powder coating is up to three times
greater when a steep surface tension gradient is purposely created through powder
blending. Surface tension gradients might also be responsible for the greater surface
roughness (observed with atomic force microscopy on lateral length scales of 100 ¼m)
that is found in coatings that contain flow agent.
Using magnetic resonance profiling coupled with dynamic light scattering, we have investigated the mechanisms leading to the formation of a partly coalesced surface layer, or ?open skin?, during film formation from waterborne polymer dispersions. We present the first use of the skewness of the distribution of free water as a model-free indicator of the spatial nonuniformity of drying. The skewness reaches a maximum at the same time at which a strong, static component, presumably originating from a skin at the film/air interface, appears in the light scattering data. Addition of salt to the dispersion increases both the skewness of the distribution of free water and the propensity for skin formation. Surprisingly, the drying is influenced not only by the concentration and valency of the ions in the salt but also by the particular ion. At intermediate particle densities, added salt strongly lowers the cooperative diffusion coefficient, Dcoop. When the particles reach close packing, Dcoop sharply increases. If the particles readily coalesce, the effects of the increased diffusivity will be counteracted, thereby inducing the formation of a skin. A modified Peclet number, Pe, using Dcoop, is proposed, so that the presence of salt is explicitly considered. This modified Pe is able to predict the nonuniformity in drying that leads to skin formation.
Gurney RS, Morse A, Siband E, Dupin D, Armes SP, Keddie JL (2015) Mechanical properties of a waterborne pressure-sensitive adhesive with a percolating poly(acrylic acid)-based diblock copolymer network: effect of pH., J Colloid Interface Sci 448 pp. 8-16
Copolymerizing an acrylic acid comonomer is often beneficial for the adhesive properties of waterborne pressure-sensitive adhesives (PSAs). Here, we demonstrate a new strategy in which poly(acrylic acid) (PAA) is distributed as a percolating network within a PSA film formed from a polymer colloid. A diblock copolymer composed of PAA and poly(n-butyl acrylate) (PBA) blocks was synthesized using reversible addition-fragmentation chain transfer (RAFT) polymerization and adsorbed onto soft acrylic latex particles prior to their film formation. The thin adsorbed shells on the particles create a percolating network that raises the elastic modulus, creep resistance and tensile strength of the final film. When the film formation occurs at pH 10, ionomeric crosslinking occurs, and high tack adhesion is obtained in combination with high creep resistance. The results show that the addition of an amphiphilic PAA-b-PBA diblock copolymer (2.0 wt.%) to a soft latex provides a simple yet effective means of adjusting the mechanical and adhesive properties of the resulting composite film.
Flexible radiation dosimeters have been produced incorporating thick films (>1 ¼m) of the semiconducting polymer
poly([9,9-dioctylfluorenyl-2,7-diyl]-co-bithiophene). Diode structures produced on aluminium-metallised poly(imide)
substrates, and with gold top contacts, have been examined with respect to their electrical properties. The results suggest
that a Schottky conduction mechanism occurs in the reverse biased diode, with a barrier to charge injection at the
aluminium electrode. Optical absorption/emission spectra reveal a band gap of 2.48 eV for the polymer. The diodes have
been used for direct charge detection of 17 keV X-rays, generated by a molybdenum source. Using operating voltages of
-10 and -50 V respectively, sensitivities of 54 and 158 nC/mGy/cm3 have been achieved. Increasing the operating
voltage shows that the diodes are stable up to approximately -200 V without significant increase in the dark current of
the device (
Keddie JL, Gorce JP, Mallégol J, McDonald PJ (2004) Understanding water-borne coatings: New techniques to answer old questions, Surface Coatings International Part A: Coatings Journal 87 (2) pp. 70-73
It is shown that a combination of pulsed-field-gradient spin-echo ~PGSE! nuclear-magnetic-resonance~NMR! restricted diffusion analysis and NMR imaging may be used to measure the spatial dependence of the droplet size distribution in the cream layer of turbid oil-in-water emulsions. 1H-13C cyclic J cross-polarization
PGSE is introduced as a technique for this purpose in cases where selective observation of the oil component ~or other carbohydrate constituent! is required. With this method, 13C nuclei are chemical shift selectively
excited by cross-polarization from coupled 1H partners. An optimum detection sensitivity is ensured by transferring the polarization back to the coupled protons with which the combined imaging and diffusion experiment is then carried out. The spatial dependence of the oil droplet size distribution was measured for a series of emulsions containing various fractions of gum xanthan thickener dissolved in the water. The experimental results are compared with a recent model of the creaming process due to Pinfield, Dickinson, and Povey @J. Colloid Interface Sci. 166, 363 ~1994!#. When no gum xanthan is present, the experimental results are in good agreement with the model. However, the model fails to describe the droplet distribution for emulsions with a gum xanthan concentration of the order of 0.1 wt %. The discrepancy is discussed in terms of depletion flocculation and depletion stabilization.
In the film formation of latex, particle deformation can occur by processes of wet sintering, dry sintering, or capillary action. When latex films dry nonuniformly and when particles deform and coalesce while the film is still wet, a detrimental skin layer will develop at the film surface. In their process model, Routh and Russel proposed that the operative particle deformation mechanism can be determined by the values of control parameters on a deformation map. Here, the film formation processes of three methyl methacrylate/butyl acrylate copolymer latexes with high glass transition temperatures (T g), ranging from 45 to 64 C, have been studied when heated by infrared radiation. Adjusting the infrared (IR) power density enables the film temperature, polymer viscosity, and evaporation rate during latex film formation to be controlled precisely. Different polymer particle deformation mechanisms have been demonstrated for the same latex under a variety of film formation process conditions. When the temperature is too high, a skin layer develops. On the other hand, when the temperature is too low, particles deform by dry sintering, and the process requires extended time periods. The deduced mechanisms can be interpreted and explained by the Routh-Russel deformation maps. Film formation of hard (high Tg) coatings is achieved without using coalescing aids that emit volatile organic compounds (VOCs), which is a significant technical achievement. © 2013 American Chemical Society.
Mallégol J, Dupont O, Keddie JL (2001) Obtaining and interpreting images of waterborne acrylic pressure-sensitive adhesives by tapping-mode atomic force microscopy, Langmuir 17 (22) pp. 7022-7031
The first atomic force microscopy (AFM) images of waterborne acrylic pressure-sensitive adhesives (PSAs) are presented along with details of their optimum scanning conditions. Driving this work is a huge practical need for information about the surface morphology of waterborne PSAs, which are deposited from colloidal dispersions to yield highly tacky, soft surfaces. These surfaces present contradictory requirements for tapping-mode AFM. Whereas soft surfaces require light tapping to avoid surface damage, tacky surfaces require energetic tapping to enable the tip to lift off of the surface. We have made a systematic study of the effects of several key parameters: the cantilever spring constant; the free amplitude of oscillation (Ao); the setpoint value (dsp); and the setpoint ratio (rsp = dsp/Ao), which we have re-defined for a soft surface to account for the indentation depth. Amplitude-distance curves were obtained from the PSA surfaces to evaluate the tip's indentation depth. Reliable images are obtained when these parameters are known and optimized. While the "true" surface of the film is actually rather smooth, images of the sub-surface particle morphology are best obtained with a stiff cantilever (spring constant of 48 N/m) and a large Ao (about 135 nm). Setting rsp close to unity minimizes the indentation of the tip and the resultant surface deformation.
Selvakumaran J, Hughes MP, Keddie JL, Ewins DJ (2002) Assessing biocompatibility of materials for implantable microelectrodes using cytotoxicity and protein adsorption studies, 2ND ANNUAL INTERNATIONAL IEEE-EMBS SPECIAL TOPIC CONFERENCE ON MICROTECHNOLOGIES IN MEDICINE & BIOLOGY, PROCEEDINGS pp. 261-264
Keddie JL, Georgiadis A, Sansom H, Muhamad F (2013) Bespoke patterned coatings via infrared radiation-assisted evaporative lithography: Moving colloids with modulated light, ABSTRACTS OF PAPERS OF THE AMERICAN CHEMICAL SOCIETY 245 AMER CHEMICAL SOC
Lopez A, Reyes Y, Asua JM, Lopez A, Degrandi-Contraires E, Creton C, Canetta E, Keddie JL, Canetta E (2013) Simultaneous free-radical and addition miniemulsion polymerization: Effect of the chain transfer agent on the microstructure of polyurethane-acrylic pressure-sensitive adhesives, Macromolecular Materials and Engineering 298 (1) pp. 53-66 Wiley-VCH Verlag Berlin
The effects of the CTA concentration on polymerization kinetics, polymer microstructure, particle morphology, and adhesive performance of waterborne hybrid PSAs prepared by simultaneous free-radical and addition miniemulsion polymerizations are studied. The development of the microstructure is shown to differ from waterborne acrylic PSAs obtained by free-radical polymerization because of the contribution of the addition reaction, which in turn causes marked differences in the adhesive performance of the final films. A computer simulation is developed to obtain detailed information about the microstructure of PU/acrylic hybrids and to correlate the microstructure with the final adhesive properties. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
Mallegol J, Gorce JP, Dupont O, Jeynes C, McDonald PJ, Keddie JL (2002) Origins and effects of a surfactant excess near the surface of waterborne acrylic pressure-sensitive adhesives, LANGMUIR 18 (11) pp. 4478-4487 AMER CHEMICAL SOC
Keddie JL, Wang T, Jurewicz I, Dalton AB, Creton C, Manea M, Asua JM (2007) Multifunctional nanocomposites of soft polymer colloids and carbon nanotubes, ABSTRACTS OF PAPERS OF THE AMERICAN CHEMICAL SOCIETY 234 AMER CHEMICAL SOC
Hellgren AC, Wallin M, Weissenborn PK, McDonald PJ, Glover PM, Keddie JL (2001) New techniques for determining the extent of crosslinking in coatings, PROGRESS IN ORGANIC COATINGS 43 (1-3) pp. 85-98 ELSEVIER SCIENCE SA
Mehrotra V, Keddie JL, Miller JM, Giannelis EP (1991) Electrically conducting glasses: incorporation of polypyrrole in a porous SiO2 matrix, Journal of Non-Crystalline Solids 136 (1-2) pp. 97-102
Electrically conducting glasses have been synthesized by incorporating polypyrrole in an SiO2 sol-gel derived glass matrix. Adsorption of pyrrole in the porous network of Cu2+-containing silica gels, in both bulk and thin film form, results in an oxidative polymerization to polypyrrole as demonstrated by electronic, infrared and Raman spectroscopies. Upon doping with iodine vapors, the polypyrrole-glass hybrids become electrically conducting with an average room temperature dc conductivity of 2 × 10-3 S/cm in the bulk and 3 × 10-4 S/cm in thin film form. DC conduction is described by a variable-range hopping model. The dielectric response of the hybrids is characteristics of conductor-insulator composites. © 1991.
The widespread use of thin films in a range of applications and industries, from coatings, inks and lithography to nano-imprinting, optoelectronics and memory devices,1 has made the understanding of thin films, particularly the changes induced by structural relaxation and solvent evaporation, very important. There is a need to know whether a film will change in dimensions after its deposition and how fast these changes will occur.
Nanocomposites of a polymer and carbon nanotubes exhibit high electrical and thermal conductivity and enhanced mechanical properties in comparison to the polymer alone. Film formation from latex dispersions is an ideal way to create nanocomposite coatings with the advantages of solvent-free processing and a high uniformity of dispersion. It is shown here that carbon nanotubes functionalised with poly(vinyl alcohol) (PVA) can be blended with two types of acrylic latex to create stable colloidal dispersions without the need for added surfactant or emulsifier. Waterborne nanocomposite films with optical transparency can be formed. Microscopic analysis shows that the PVA-functionalized nanotubes are finely and uniformly dispersed in the polymer matrix.
Keddie JL, Ekanayake P, Koenig AM, Weerakkody TG, Barber N, Johannsmann D, Sear RP, McDonald PJ (2007) Influence of the colloidal stability of latex particles on their distribution in drying films, ABSTRACTS OF PAPERS OF THE AMERICAN CHEMICAL SOCIETY 234 AMER CHEMICAL SOC
We present a simple technique to switch off the tack adhesion in selected areas of a colloidal nanocomposite adhesive. It is made from a blend of soft colloidal polymer particles and hard copolymer nanoparticles. In regions that are exposed to IR radiation, the nanoparticles sinter together to form a percolating skeleton, which hardens and stiffens the adhesive. The tack adhesion is lost locally. Masks can be made from silicone-coated disks, such as coins. Under the masks, adhesive island regions are defined with the surrounding regions being a nontacky coating. When optimizing the nanocomposite's adhesive properties, the addition of the hard nanoparticles raises the elastic modulus of the adhesive significantly, but adhesion is not lost because the yield point remains relatively low. During probe-tack testing, the soft polymer phases yield and enable fibrillation. After heating under IR radiation, the storage modulus increases by a factor of 5, and the yield point increases nearly by a factor of 6, such that yielding and fibrillation do not occur in the probe-tack testing. Hence, the adhesion is lost. Loading and unloading experiments indicate that a rigid skeleton is created when the nanoparticles sinter together, and it fractures under moderate strains. This patterning method is relatively simple and fast to execute. It is widely applicable to other blends of thermoplastic hard nanoparticles and larger soft particles.
Wang T, Liu D, Keddie JL (2007) An alternative approach to the modification of talc for the fabrication of polypropylene/Talc composites, JOURNAL OF APPLIED POLYMER SCIENCE 106 (1) pp. 386-393 JOHN WILEY & SONS INC
Udagama R, de las Heras Alarcón C, Keddie JL, Tsavalas JG, Bourgeat-Lami E, Mckenna TFL (2014) Acrylic-alkyd hybrids: Secondary nucleation, particle morphology, and limiting conversions, Macromolecular Reaction Engineering 8 (9) pp. 622-638
© 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.The chemical incorporation of an unsaturated alkyd into an acrylic polymer created via miniemulsion polymerisation was studied. The variation of the number ratio of polymer particles to initial droplets with conversion, and changes in individual monomer conversions with increasing alkyd levels were the main quantities used to study the effect of increasing alkyd quantity in the hybrid system. Homogeneous nucleation was more significant in systems rich in the more hydrophilic methyl methacrylate (MMA). Changes in particle morphology with monomer conversion, as well as limited monomer conversion were observed. The results emphasize the importance of proper pairing of the miscibility between the specific acrylics and alkyds used in these hybrid polymers. The polymerization of miniemulsions of acrylic monomer/alkyd mixtures is studied. It is shown that complete conversion can only be obtained if secondary nucleation is allowed to occur at high alkyd contents. In addition, it is demonstrated that the choice of initiator can have a significant impact on particle morphology and the quality of the resulting films.
Wallin M, Glover PM, Hellgren AC, Keddie JL, McDonald PJ (2000) Depth profiles of polymer mobility during the film formation of a latex dispersion undergoing photoinitiated cross-linking, MACROMOLECULES 33 (22) pp. 8443-8452 AMER CHEMICAL SOC
KEDDIE J, JONES R, CORY R (1994) SIZE-DEPENDENT DEPRESSION OF THE GLASS-TRANSITION TEMPERATURE IN POLYMER-FILMS, EUROPHYSICS LETTERS 27 (1) pp. 59-64
Soft adhesives require an optimum balance of viscous and elastic properties. Adhesion is poor when the material is either too solidlike or too liquidlike. The ability to switch tack adhesion off at a desired time has many applications, such as in recycling, disassembly of electronics, and painless removal of wound dressings. Here, we describe a new strategy to switch off the tack adhesion in a model nanocomposite adhesive in which temperature is the trigger. The nanocomposite comprises hard methacrylic nanoparticles blended with a colloidal dispersion of soft copolymer particles. At relatively low volume fractions, the nanoparticles (50 nm diameter) accumulate near the film surface, where they pack around the larger soft particles (270 nm). The viscoelasticity of the nanocomposite is adjusted via the nanoparticle concentration. When the nanocomposite is heated above the glass transition temperature of the nanoparticles (T(g) = 130 °C), they sinter together to create a rigid network that raises the elastic modulus at room temperature. The tackiness is switched off. Intense infrared radiation is used to heat the nanocomposites, leading to a fast temperature rise. Tack adhesion is switched off within 30 s in optimized compositions. These one-way switchable adhesives have the potential to be patterned through localized heating.
Mills CA, Chan Y-F, Intaniwet A, Nisbet A, Keddie JL, Sellin PJ (2013) Direct Detection of 6 MV X-rays from a Medical Linear Accelerator using a Semiconducting Polymer Diode, Physics in Medicine and Biology 58 (13) pp. 4471-4482 Institute of Physics
Recently, a new family of low-cost x-radiation detectors have been developed,
based on semiconducting polymer diodes, which are easy to process,
mechanically flexible, relatively inexpensive, and able to cover large areas.
To test their potential for radiotherapy applications such as beam monitors or
dosimeters, as an alternative to the use of solid-state inorganic detectors, we
present the direct detection of 6 MV x-rays from a medical linear accelerator
using a thick film, semiconducting polymer detector. The diode was subjected
to 4 ms pulses of 6 MV x-rays at a rate of 60 Hz, and produces a linear increase
in photocurrent with increasing dose rate (from 16.7 to 66.7 mGy s(?1)). The
sensitivity of the diode was found to range from 13 to 20 nC mGy(?1) cm(?3),
for operating voltages from ?50 to ?150 V, respectively. The diode response
was found to be stable after exposure to doses up to 15 Gy. Testing beyond this
dose range was not carried out. Theoretical calculations show that the addition
of heavy metallic nanoparticles to polymer films, even at low volume fractions,
increases the x-ray sensitivity of the polymer film/nanoparticle composite
so that it exceeds that for silicon over a wide range of x-ray energies. The
possibility of detecting x-rays with energies relevant to medical oncology
applications opens up the potential for these polymer detectors to be used
in detection and imaging applications using medical x-ray beams.
Richardson H, Sferrazza M, Keddie JL (2003) Influence of the glass transition on solvent loss from spin-cast glassy polymer thin films., Eur Phys J E Soft Matter 12 Suppl 1 pp. S87-S91
The interdependence of solvent loss and vitrification in spin-cast poly(methyl methacrylate) thin films is explored. Fast measurements of decreases in film thickness, achieved with ellipsometry, indicate that the rate of solvent (toluene) loss decreases sharply when the solvent volume fraction phi(solv) falls below about 0.15 and the film vitrifies. Ellipsometry and microgravimetry show that solvent is lost from a glassy thin film (150 nm thick) over of a period of more than ten hours, which is much longer than would be required if it was limited by diffusion in the glass. These results support the recently-proposed idea that the compression of the glass creates an energy barrier that slows down solvent loss.
Clough AS, Jenneson PM, Keddie JL (1997) Ion beam analysis of small molecule diffusion in polymers, Annual Technical Conference - ANTEC, Conference Proceedings 2 pp. 2211-2215
Ion beam analysis has been applied to a variety of problems involving the diffusion of small molecules in polymeric matrices. Energy loss techniques have been used to study the diffusivity of dye molecules and water. Beam traversing techniques have determined water concentrations in hydrophilic polymers over distances of several mm. The suite of techniques available allows the analysis of nearly every element.
Bennett G, Gorce JP, Keddie JL, McDonald PJ, Berglind H (2003) Magnetic resonance profiling studies of the drying of film-forming aqueous dispersions and glue layers., Magn Reson Imaging 21 (3-4) pp. 235-241
We report magnetic resonance profiling experiments to monitor (i) the drying of alkyd emulsion layers, (ii) the cure of wood glue layers and (iii) water transport through glue lines. The alkyd drying is a two stage process. We report new results which support previous evidence that the alkyd drops do not coalesce until the water fraction is below circa 0.02. The profiles recorded from glue layers suggest that MR is a sensitive probe of the curing process and barrier properties of the glue. The measurements were made using GARField (stray field, STRAFI like) magnetic resonance profiling and an improved GARField magnet design characterized by two values of the gradient-to-field strength ratio at two locations offering the same field strength is also reported.
Tzitzinou A, Jenneson PM, Clough AS, Keddie JL, Lu JR, Zhdan P, Treacher KE, Satguru R (1999) Surfactant concentration and morphology at the surfaces of acrylic latex films, Progress in Organic Coatings 35 (1-4) pp. 89-99
The final outcome of surfactants during latex film formation is a topic of ongoing concern and interest. In this study of an acrylic latex containing an anionic surfactant, two notable phenomena are observed. (1) A higher surfactant concentration is present at the air surface of the latex films, regardless of the film-forming temperature and time. In some cases, surfactant is not visible in an atomic force microscope (AFM) image as a separate phase, but compositional profiles obtained with Rutherford backscattering spectrometry (RBS) reveal an enhanced concentration of surfactant over a depth from the surface that is comparable to the latex particle diameter. (2) The surfactant features that are imaged with the AFM evolve from a thin uniform layer, to a 'finger-like' morphology, to small flat droplets, and finally to larger, hemispherical 'blobs'. We suggest that surfactant is first deposited from the air/water interface onto the latex surface during the drying process. During this progression in the morphology of the surfactant, the ratio of the surface area-to-volume decreases. We speculate that this phenomenon is driven by a reduction in surface energy.
Nikonenko NA, Bushnak IA, Keddie JL (2009) Spectroscopic ellipsometry of mucin layers on an amphiphilic diblock copolymer surface, Applied Spectroscopy 63 (8) pp. 889-898
Both visible and infrared (IR) spectroscopic ellipsometry have been employed to study the structure of thin layers of bovine submaxillary mucin (BSM) adsorbed on poly(acrylic acid-block-methyl methacrylate) (PAA-b-PMMA) copolymer and poly(methyl methacrylate) (PMMA) surfaces at three pH values (3, 7, and 10). The adsorbed mucin layer on the copolymer surface had the greatest thickness (17 nm) when adsorbed from a mucin solution at a pH of 3. For the first time, IR ellipsometry was used to identify adhesive interactions and conformational changes in mucin/polymer double layers. After applying the regularized method of deconvolution in the analysis, the formation of hydrogen bonds between the carboxyl groups of the BSM and PAA-b-PMMA copolymer in double layers has been found. The IR ellipsometry data, in agreement with the visible ellipsometry analysis, indicate the pH dependence of adhesion of mucin to the copolymer surface. There is an increase in the amount of hydrogen-bonded carboxyl groups in mucin deposited at a pH of 3. There is no evidence that the amide groups of the mucin participate in this bonding. At the lower pH, the IR ellipsometry spectra after deconvolution reveal an increase in the proportion of ²-sheets in the BSM upon adsorption on the copolymer surface, indicating a more unfolded, aggregated structure. The IR ellipsometry data also indicated some changes in the conformational states of the side groups in the copolymer induced by entanglements and bonding interactions with the mucin macromolecules. Deconvolution provides an unprecedented level of information from the IR ellipsometry spectra and yields important insights. © 2009 Society for Applied Spectroscopy.
Murphy EF, Keddie JL, Lu JR, Brewer J, Russell J (1999) The reduced adsorption of lysozyme at the phosphorylcholine incorporated polymer/aqueous solution interface studied by spectroscopic ellipsometry., Biomaterials 20 (16) pp. 1501-1511
Coating hydrogel polymers onto solid substrates can reduce the adsorption of proteins onto these surfaces, but the extent of the reduction in protein adsorption is strongly dependent on how the surface layer is coated. We have examined the effect of coating conditions on the structure of thin polymer films formed from a number of poly(methacrylate)-based hydrogel polymers via the dip-coating method. We show in this work how the polarity of the solvent, the speed of lifting, and the annealing temperature affect the thickness and uniformity of ultrathin phosphorylcholine (PC)-incorporated polymer films coated on the surface of native oxide on silicon and the subsequent interaction of these coated surfaces with lysozyme molecules. Our results show that the uniformity of the polymer film, and thus the smoothness of the outer film surface, influence the extent of reduction in protein adsorption. We suggest that the reduction in lysozyme adsorption is the result of a layer of PC groups on the surface of the polymer film. The improvement of the smoothness of the film results in the formation of a close-packed PC layer on the outer surface of the polymer film, leaving few defects or cavities on which protein molecules can bind.
Bero MA, Gilboy WB, Glover PM, Keddie JL (1999) Three-dimensional radiation dose measurements with Ferrous Benzoic Acid Xylenol Orange in Gelatin gel and optical absorption tomography, Nuclear Instruments and Methods in Physics Research, Section A: Accelerators, Spectrometers, Detectors and Associated Equipment 422 (1-3) pp. 617-620
The optical characteristics of a Ferrous Benzoic Acid Xylenol Orange in Gelatin (FBXG) gel have been studied over the wavelength range 300-700 nm as a function of radiation dose. The unirradiated gel exhibits a strong absorption peak at 440 nm; with increasing dose this peak starts to reduce in intensity while a new broad peak centred at 585 nm begins to appear. Using 60Co gamma rays the absorption coefficients for these two peaks were found to vary linearly with dose up to at least 30Gy with slopes of -0.028cm-1 Gy-1 (440nm) and 0.069cm-1 Gy-1 (585nm). The pre- and post-irradiation stability was studied and absorbance changes of less than 1% per hour were observed over periods of a few days. The NMR response of FBXG gels was found to be marginally reduced compared to the standard Fricke dosemeter in gel form and the NMR technique is much less sensitive than the optical readout method. Tissue equivalent phantoms with dimensions of several centimetres can be constructed of FBXG gel and Optical Absorption Tomography (OAT) used to measure the three-dimensional dose distribution within them after exposure to radiation beams. The OAT technique is a much simpler and cheaper method of readout compared with Magnetic Resonance Imaging (MRI). © 1999 Elsevier Science B.V. All rights reserved.
Duckworth P, Richardson H, Carelli C, Keddie JL (2005) Infrared ellipsometry of interdiffusion in thin films of miscible polymers, Surface and Interface Analysis 37 (1) pp. 33-41
A new application of infrared ellipsometry is reported. Specifically, the interdiffusion between thin films of miscible polymers - poly(methyl methacrylate) and poly(vinylidene fluoride) - is detected in a non-invasive measurement. A novel technique of data analysis for interdiffusion was developed and is described. The validity of the approach is supported by simulations of diffusion in a bilayer. The onset of extensive interdiffusion over a time period of 15 min occurs at a temperature of 160°C. At a temperature of 190°C, the data show that complete mixing of a bilayer (850 nm thick) occurs within 30s, which is consistent with previously reported values of the mutual diffusion coefficient. Infrared ellipsometry is non-invasive, applicable at elevated temperatures and relatively fast and sensitive. Although, in these measurements, it was unable to determine a concentration profile at the interface, infrared ellipsometry was used successfully to detect when interdiffusion had occurred. Hence, it is a useful means for screening polymer pairs for miscibility. Copyright © 2004 John Wiley & Sons, Ltd.
Films cast from multiphase polymer particles have the potential to combine the properties of their components synergistically. The properties of the film depend on the hybrid polymer architecture and the film morphology. However, how the polymer microstructure and particle morphology are transformed during film formation to determine the film morphology is not well understood. Here, using waterborne alkyd-acrylic nanocomposite particles in a case study, it was found that phase migration leading to the formation of aggregates occurred during film formation. A coarse-grained Monte Carlo model was developed to account for the effects of polymer microstructure and particle morphology on the morphology of the film. The model was validated by comparing its predictions with the observed effects, and then used to explore combinations of polymer microstructure and particle morphology not attainable with the system used as a case study. Significantly, the compatibility of the phases was found to have a greater influence than the morphology of the particles in determining the film structure.
The film formation of an acrylate latex with a glass-transition temperature of 38 °C has been achieved through the use of near-infrared (NIR) radiative heating. A hard, crack-free coating was obtained without the addition of plasticizers. Sintering of acrylate particles was confirmed through measurements using atomic force microscopy. The addition of an NIR-absorbing polymer increased the rate of particle deformation such that it was significantly greater than obtained in a convection oven at 60 °C. The results are consistent with a lower polymer viscosity under infrared radiation, according to a simple analysis using a standard model of sintering.
Keddie J, Mallégol J, Dupont O (2001) The technological and environmental pressures on advanced adhesives, Materials World 9 (11) pp. 22-24
The pressure-sensitive adhesive (PSA) industry is facing ongoing challenges to further develop its technologies and environmental performance. However, it's evident that the materials scientists' response to these challenges is leading to the development of products that are better for the environment and for human health. This paper looks at how PSAs are responding to environmental and technological challenges, and their increased use in high-performance applications.
Keddie JL (1997) Film formation of latex, Materials Science and Engineering R: Reports 21 (3) pp. 101-170
Latex film formation, the process by which an aqueous dispersion of polymer particles is transformed into a continuous material, has a direct bearing on the final film morphology and properties. Each of the primary stages of film formation (evaporative drying and ordering; particle deformation; and polymer interdiffusion) have been studied experimentally. Recently-developed non-invasive techniques, including direct nonradiative energy transfer, atomic force microscopy, small angle neutron scattering, environmental scanning electron microscopy, and various optical techniques have greatly enhanced the study of these stages. Even so, the exact cause (or causes) of particle deformation is still a topic of considerable debate. Several factors are experimentally known to influence latex film formation: the ambient conditions; the presence of surfactants, plasticizers and pigments; and latex particle structure. An important aim in the study of latex film formation is to understand the mechanisms by which these and other factors affect the process. New challenges lie in the study of film formation of core-shell latices, latex blends and new compositions. © 1997 Elsevier Science S.A.
Keddie JL, Gurney R, Dupin D, Siband E (2013) Large-area patterning of the tackiness of a colloidal nanocomposite adhesive by sintering of nanoparticles under IR radiation, ABSTRACTS OF PAPERS OF THE AMERICAN CHEMICAL SOCIETY 245 AMER CHEMICAL SOC
Jurewicz I, Worajittiphon P, King AA, Sellin PJ, Keddie JL, Dalton AB (2011) Locking carbon nanotubes in confined lattice geometries--a route to low percolation in conducting composites., J Phys Chem B 115 (20) pp. 6395-6400
A significant reduction in the electrical percolation threshold is achieved by locking carbon nanotubes (CNTs) in a predominantly hexagonally close-packed (HCP) colloidal crystal lattice of partially plasticized latex particles. Contrary to other widely used latex processing where CNTs are randomly distributed within the latex matrix, for the first time, we show that excluding CNTs from occupying the interior volume of the latex particles promotes the formation of a nonrandom segregated network. The electrical percolation threshold is four times lower in an ordered segregated network made with colloidal particles near their glass transition temperature (T(g)) in comparison to in a random network made with particles at a temperature well above the T(g). This method allows for a highly reproducible way to fabricate robust, stretchable, and electrically conducting thin films with significantly improved transparency and lattice percolation at a very low CNT inclusion which may find applications in flexible and stretchable electronics as well as other stretchable technologies. For instance, our technology is particularly apt for touch screen applications, where one needs homogeneous distribution of the conductive filler throughout the matrix.
KEDDIE J, JONES R (1995) GLASS-TRANSITION BEHAVIOR IN ULTRA-THIN POLYSTYRENE FILMS, ISRAEL JOURNAL OF CHEMISTRY 35 (1) pp. 21-26
Keddie JL, Ciampi E, McDonald PJ, Salamanca JM (1999) Magnetic resonance imaging of the film formation of waterborne coatings., ABSTRACTS OF PAPERS OF THE AMERICAN CHEMICAL SOCIETY 218 pp. U621-U621
Styrkas D, Doran SJ, Gilchrist T, Keddie JL, Lu JR, Murphy E, Sackin R, Su TJ, Tzitzinou A (1999) Application of ellipsometry to polymers at interfaces and in thin films, POLYMER SURFACES AND INTERFACES III pp. 1-42
Sackin R, Ciampi E, Godward J, Keddie JL, McDonald PJ (2001) Fickian ingress of binary solvent mixtures into glassy polymer, MACROMOLECULES 34 (4) pp. 890-895 AMER CHEMICAL SOC
Agirre A, Heras-Alarcón CDL, Wang T, Keddie JL, Asua JM (2010) Waterborne, semicrystalline, pressure-sensitive adhesives with temperature-responsiveness and optimum properties, ACS Applied Materials and Interfaces 2 (2) pp. 443-451
The synthesis and resulting temperature-responsive properties of semicrystalline waterborne pressure-sensitive adhesives (PSAs) were investigated. A crystalline polymer fraction was produced in situ within waterborne particles by miniemulsion polymerization of non-branched long chain acrylates. The degree of crystallinity was controlled by copolymerization with a short chain acrylate. The polymerization strategy determined the polymer architecture and film structure, which then influenced the adhesion properties. The high sensitivity of the adhesion strength of these PSAs to temperature, in the range around the crystal melting point, opens up the possibility of designing temperature-responsive adhesives. With the right distribution and concentration of crystalline polymers, a simultaneous increase in both the peel strength and the shear resistance was obtained, which is a combination that is often not found when optimizing adhesive properties. © 2010 American Chemical Society.
KEDDIE J, BRAUN P, GIANNELIS E (1994) INTERRELATIONSHIP BETWEEN DENSIFICATION, CRYSTALLIZATION, AND CHEMICAL EVOLUTION IN SOL-GEL TITANIA THIN-FILMS, JOURNAL OF THE AMERICAN CERAMIC SOCIETY 77 (6) pp. 1592-1596
Carter FT, Kowalczyk RM, Millichamp I, Chainey M, Keddie JL (2014) Correlating particle deformation with water concentration profiles during latex film formation: reasons that softer latex films take longer to dry., Langmuir 30 (32) pp. 9672-9681
During the past two decades, an improved understanding of the operative particle deformation mechanisms during latex film formation has been gained. For a particular colloidal dispersion, the Routh-Russel deformation maps predict the dominant mechanism for particle deformation under a particular set of conditions (evaporation rate, temperature, and initial film thickness). Although qualitative tests of the Routh-Russel model have been reported previously, a systematic study of the relationship between the film-formation conditions and the resulting water concentration profiles is lacking. Here, the water distributions during the film formation of a series of acrylic copolymer latexes with varying glass-transition temperatures, Tg (values of -22, -11, 4, and 19 °C), have been obtained using GARField nuclear magnetic resonance profiling. A significant reduction in the rate of water loss from the latex copolymer with the lowest Tg was found, which is explained by its relatively low polymer viscosity enabling the growth of a coalesced skin layer. The set of processing parameters where the drying first becomes impeded occurs at the boundary between the capillary deformation and the wet sintering regimes of the Routh-Russel model, which provides strong confirmation of the model's validity. An inverse correlation between the model's dimensionless control parameter and the dimensionless drying time is discovered, which is useful for the design of fast-drying waterborne films.
Bradley M, Liu D, Keddie JL, Vincent B, Burnett G (2009) The Uptake and Release of Cationic Surfactant from polyampholyte Microgel Particles in Dispersion and as an Adsorbed Monolayer, LANGMUIR 25 (17) pp. 9677-9683 AMER CHEMICAL SOC
A new class of X-ray sensor ? in which there is a blend of poly(triarylamine) (PTAA) and 6,13-bis(triisopropylsilylethynyl) (TIPS)-pentacene in the active layer of a diode structure ? has been developed. The crystalline pentacene provides a fast route for charge carriers and leads to enhanced performance of the sensor. The first time-of-flight charge-carrier mobility measurement of this blend is reported. The mobility of PTAA and TIPS-pentacene in a 1:25 molar ratio was found to be 2.2 × 10?5 cm2 V?1 s?1 (averaged for field strengths between 3 × 104 and 4 × 105 V cm?1), which is about 17 times higher than that obtained in PTAA over the same range of field strengths. This higher mobility is correlated with a fourfold increase in the X-ray detection sensitivity in the PTAA:TIPS-pentacene devices.
Keddie JL, Gorce JP, Mallegol J, Wallin M, Barry AM, Ciampi E, Motiejauskaite A, Glover PM, McDonald PJ, Weissenborn PK (2001) MR profiling of film formation and crosslinking in waterborne alkyd emulsions and emulsion paints., ABSTRACTS OF PAPERS OF THE AMERICAN CHEMICAL SOCIETY 222 pp. U378-U378 AMER CHEMICAL SOC
Wang T, Lei C-H, Liu D, Manea M, Asua JM, Creton C, Dalton AB, Keddie JL (2008) A molecular mechanism for toughening and strengthening waterborne nanocomposites, ADVANCED MATERIALS 20 (1) pp. 90-+ WILEY-V C H VERLAG GMBH
Keddie JL, Meredith P, Jones RAL, Donald AM (1998) Film formation of latices, MODERN ASPECTS OF COLLOIDAL DISPERSIONS pp. 51-59
Routh AF, Keddie J (2010) Fundamentals of Latex Film Formation: Processes and Properties, Springer Verlag
This book introduces the reader to latex, which is a colloidal dispersion of polymer particles in water, and explains how useful products are made from it.
The morphology of pressure sensitive adhesives (PSAs), especially at the surface in contact with a release liner, is expected to have a dominant influence on the tack strength and energy in an application. We have used tapping-mode atomic force microscopy to determine the morphology at the surfaces of freshly-cast waterborne acrylic PSAs over lateral length scales of a few m. We demonstrate that topographical features on silicone release liners can be used to pattern the PSA surface in contact with it. Control of the texture of a PSA surface can potentially be exploited to tailor its properties. Latex particle boundaries are much better defined at the air surface of the PSA in comparison to its back face. A series of experiments suggests that this difference results from the distribution of water-soluble species within the dry film. The pressures and processes involved in the transfer lamination process do not alter the PSA morphology. The first reported AFM images of the response of these materials to pressure and shear provide insight into the deformation mechanisms. Amplitude-distance curves on PSA surfaces show that there is a small decrease in tack and an increase in stiffness after ageing for 13 months.
Utgenannt A, Maspero R, Fortini A, Turner R, Florescu M, Jeynes C, Kanaras A, Muskens O, Sear RPL, Keddie JL (2016) Fast Assembly of Gold Nanoparticles in Large-Area 2-D Nanogrids Using a One-Step, Near-Infrared Radiation-Assisted Evaporation Process, ACS Nano 10 (2) pp. 2232-2242
American Chemical Society
When fabricating photonic crystals from suspensions in volatile liquids using the horizontal deposition method, the conventional approach is to evaporate slowly to increase the time for particles to settle in an ordered, periodic close-packed structure. Here, we show that the greatest ordering of 10 nm aqueous gold nanoparticles (AuNPs) in a template of larger spherical polymer particles (mean diameter of 338 nm) is achieved with very fast water evaporation rates obtained with near-infrared radiative heating. Fabrication of arrays over areas of a few cm2 takes only seven minutes. The assembly process requires that the evaporation rate is fast relative to the particles? Brownian diffusion. Then a two-dimensional colloidal crystal forms at the falling surface, which acts as a sieve through which the AuNPs pass, according to our Langevin dynamics computer simulations. With sufficiently fast evaporation rates, we create a hybrid structure consisting of a two-dimensional AuNP nanoarray (or ?nanogrid?) on top of a three-dimensional polymer opal. The process is simple, fast and one-step. The interplay between the optical response of the plasmonic Au nanoarray and the microstructuring of the photonic opal results in unusual optical spectra with two extinction peaks, which are analyzed via finite-difference time-domain method simulations. Comparison between experimental and modelling results reveals a strong interplay of plasmonic modes and collective photonic effects, including the formation of a high-order stop band and slow-light enhanced plasmonic absorption. The structures, and hence their optical signatures, are tuned by adjusting the evaporation rate via the infrared power density.
In simulations and experiments, we study the drying of films containing mixtures of large and small colloidal particles in water. During drying, the mixture stratifies into a layer of the larger particles at the bottom with a layer of the smaller particles on top. We developed a model to show that a gradient in osmotic pressure, which develops dynamically during drying, is responsible for the segregation mechanism behind stratification.
Colloidal nanocomposite adhesives are made by blending soft adhesive particles with hard nanoparticles (NPs) that sit at the particle boundaries to create a percolating phase. When the nanocomposite is heated with infrared (IR) radiation, the NPs sinter together to create a rigid structure that hardens the composite and thereby switches off the tack adhesion. It is discovered that the IR power density of an irradiation for 20 s must exceed a threshold value of 1.07 W cm before the tack is switched off. At lower power densities, an analysis of the sintering of the NPs shows that there is not sufficient time to link them together into a rigid structure. These results reveal that the switching of colloidal nanocomposite adhesives can be easily controlled through the IR power density and the time of the exposure. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
When films are deposited from mixtures of colloidal particles of two different sizes, a diverse range of functional structures can result. One structure of particular interest is a stratified film in which the top surface layer has a composition different than in the interior. Here, we explore the conditions under which a stratified layer of small particles develops spontaneously in a colloidal film that is cast from a binary mixture of small and large polymer particles that are suspended in water. A recent model, which considers the cross-interaction between the large and small particles (Zhou et al., Phys. Rev. Lett. (2017) 118, 108002), predicts that stratification will develop from dilute binary mixtures when the particle size ratio (a), initial volume fraction of small particles (f
s), and Péclet number are high. In experiments and Langevin dynamics simulations, we systematically vary a and fs in both dilute and concentrated suspensions. We find that stratified films develop when f
s is increased, which is in agreement with the model. In dilute suspensions, there is reasonable agreement between the experiments and the Zhou et al. model. In concentrated suspensions, stratification occurs in experiments only for the higher size ratio a = 7. Simulations using a high Péclet number, additionally find stratification with a = 2, when f
s is high enough. Our results provide a quantitative understanding of the conditions under which stratified colloidal films assemble. Our research has relevance for the design of coatings with targeted optical and mechanical properties at their surface.
Martin-Fabiani I, Fortini A, Lesage de la Haye J, Koh M, Taylor SE, Bourgeat-Lami E, Lansalot M, D?Agosto F, Sear RPL, Keddie JL (2016) pH-Switchable Stratification of Colloidal Coatings: Surfaces ?On Demand?, ACS Applied Materials and Interfaces 8 (50) pp. 34755-34761
American Chemical Society
Stratified coatings are used to provide properties at a surface, such as hardness or refractive index, which are different from underlying layers. Although time-savings are offered by self-assembly approaches, there have been no methods yet reported to offer stratification on demand. Here, we demonstrate a strategy to create self-assembled stratified coatings, which can be switched to homogenous structures when required. We use blends of large and small colloidal polymer particle dispersions in water that self-assemble during drying because of an osmotic pressure gradient that leads to a downward velocity of larger particles. Our confocal fluorescent microscopy images reveal a distinct surface layer created by the small particles. When the pH of the initial dispersion is raised, the hydrophilic shells of the small particles swell substantially, and the stratification is switched off. Brownian dynamics simulations explain the suppression of stratifi-cation when the small particles are swollen as a result of reduced particle mobility, a drop in the pressure gradient, and less time available before particle jamming. Our strategy paves the way for applications in antireflection films and pro-tective coatings in which the required surface composition can be achieved on demand, simply by adjusting the pH prior to deposition.
We advance the quantitative study of nucleation by combining the study of hundreds of samples, with statistical tests for reproducibility, and for well-defined nucleation rates. Unlike in most previous work, we find that in the samples that nucleate after the first hour of our experiment the equilibrium glycine polymorph predominates over the alpha form.
Dip coating is a very common process in food manufacturing. Controlling the thickness of the coating is key to deliver the desired sensorial properties and to be compliant with the product?s nutritional claims. Whilst dip coating with Newtonian liquids is physically well understood, coating food products almost invariably involve liquids with more complex rheology. This makes the process more difficult to design and control and reduces the coating homogeneity. Developing novel food products with improved nutritional attributes often calls for reducing the coating thickness and non-homogeneity should be avoided to guarantee the quality of the final product. In this study, we focused on the coating of a flat surface using Carbopol solutions and a commercial ketchup, following a Herschel-Bulkley rheological model. The final average coating thickness was always significantly lower than the critical thickness that can be estimated from liquid density and yield stress. Liquids with a yield stress in the range 4-56 Pa were considered in this study and the steady withdrawal speed from the bath was varied in the range 0.1-20 mm/s. The resulting average coating thickness and its uniformity are discussed. The results are interpreted in the context of an existing theory for dip coating with liquids with a yield stress. This study paves the way toward an integrated design of the coating process and the liquid rheology of foods, such as chocolate or ketchup. This can enable the development of new food products allying improved nutrition, a consumer preferred sensory profile and cost.
Developing the use of polymers from renewable sources to build hydrogels with tailored mechanical
properties has become an increasing focus of research. The impact of the thermo-reversible physical
networks of gelatin (arising from the formation of triple-helices) on the structure formation of a chemical
network, obtained by cross-linking with glutaraldehyde (a non-catalytic cross-linker), was studied using
optical rotation, oscillatory rheology and large strain mechanical deformation. We observed a direct
correlation between the storage shear modulus of the chemical network grown in the gel state (i.e.
simultaneously with the physical network) and the amount of gelatin residues in the triple-helix
conformation (Ç). Since Ç is directly affected by temperature, the value of the storage modulus is also
sensitive to changes in the temperature of gel formation. Ç values as low as 12% lead to an increase of the
shear storage modulus of the cross-linked gel by a factor of 2.7, when compared to a chemical network
obtained in the sol state (i.e. in the absence of a physical network). Our results show that the physical
network acts as a template, which leads to a greater density of the chemical cross-links and a
corresponding higher elastic modulus, beyond what is otherwise achieved in the absence of a physical
Most substances can crystallise into two or more different crystal lattices, called polymorphs. Despite this,
there are no systems in which we can quantitatively predict the probability of one competing polymorph
forming, instead of the other. We address this problem using large scale (hundreds of events) studies of the
competing nucleation of the alpha and gamma polymorphs of glycine. In situ Raman spectroscopy is used
to identify the polymorph of each crystal. We find that the nucleation kinetics of the two polymorphs is
very different. Nucleation of the alpha polymorph starts off slowly but accelerates, while nucleation of the
gamma polymorph starts off fast but then slows. We exploit this difference to increase the purity with which
we obtain the gamma polymorph by a factor of ten. The statistics of the nucleation of crystals is analogous
to that human mortality, and using a result from medical statistics we show that conventional nucleation
data can say nothing about what, if any, are the correlations between competing nucleation processes. Thus
we can show that it is impossible to disentangle the competing nucleation processes. We also find that the
growth rate and the shape of a crystal depends on when it nucleated. This is new evidence that nucleation
and growth are linked.
A major drawback of conventional emulsion polymers arises from the presence of migrating low molecular weight surfactants that contribute to poor water barrier properties and low adhesion to substrates. In this paper, we demonstrate how living polymer chains obtained by reversible addition-fragmentation chain transfer (RAFT) can be used as an efficient stabilizer in emulsion polymerization, leading to the production of surfactant-free latexes, which then form crosslinked films with beneficial properties. Hydrophilic poly(methacrylic acid) (PMAA) chains obtained by RAFT performed in water are used to mediate emulsion polymerization and produce film-forming latex particles from mixtures of methyl
methacrylate, n-butyl acrylate and styrene. Stable dispersions of particles with sizes between 100 and 200 nm are obtained, with very low amounts of coagulum (
The presence of low molar mass surfactants in latex films results in detrimental effects on their water permeability, gloss and adhesion. For applications as coatings, there is a need to develop formulations that do not contain surfactants and that have better water barrier properties. Having previously reported the synthesis of surfactant-free latex particles in water using low amounts (
Colloidal polymer composites, in which polymer particles are blended with a filler, are widely used in applications including pharmaceuticals, crop protection, inks, and protective coatings. It is generally found that the presence of hard particulate fillers will increase the elastic modulus of a polymer colloid composite. However, the influence of the size of the filler particle on the large-strain deformation and fracture and on the viscoelastic characteristics, including creep, is not well explored. We hypothesize that the size ratio of the filler to the colloidal polymer will play a critical role in determining the properties of the composite.
Colloidal composites were prepared by blending soft polymer colloids (as a binder) with calcium carbonate fillers having four different sizes, spanning from 70 nm to 4.5 mm. There is no bonding between the filler and matrix in the composites. The large-strain deformation, linear viscoelasticity, and creep were determined for each filler size for increasing the filler volume fractions (fCC). Weibull statistics were used to analyze the distributions of strains at failure.
We find that the inclusion of nano-fillers leads to brittle fracture at a lower fCC than when mm-size fillers are used. The data interpretation is supported by Weibull analysis. However, for a given fCC, the storage modulus is higher in the rubbery regime, and the creep resistance is higher when nanoparticles are used. Using scanning electron microscopy to support our arguments, we show that the properties of colloidal composites are correlated with their microstructure, which can be altered through control of the filler:polymer particle size ratio. Hard nanoparticles pack efficiently around larger particles to provide reinforcement (manifested as a higher storage modulus and greater creep resistance), but they also introduce weak points that lead to brittleness.
The use of 2,3,4,5,6-pentafluorobenzyl methacrylate (PFBMA) as a core-forming monomer in ethanolic RAFT dispersion polymerization formulations is presented. Poly[poly(ethylene glycol) methyl ether methacrylate] (pPEGMA) macromolecular chain transfer agents were chain extended with PFBMA leading to nanoparticle formation via polymerization-induced self-assembly (PISA). pPEGMA-pPFBMA particles exhibited the full range of morphologies (spheres, worms, and vesicles) including pure and mixed phases. Worm phases formed gels that underwent a thermo-reversible degelation and morphological transition to spheres (or spheres and vesicles) upon heating. Post-synthesis, the pPFBMA cores were modified through thiol?para-fluoro substitution reactions in ethanol using 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) as the base. For monothiols, conversions were 64% (1-octanethiol) and 94% (benzyl mercaptan). Spherical and worm-shaped nano-objects were core cross-linked using 1,8-octanedithiol, which prevented their dissociation in non-selective solvents. For a temperature-responsive worm sample, cross-linking additionally resulted in the loss of the temperature-triggered morphological transition. The use of the reactive monomer PFBMA in PISA formulations presents a simple method to prepare well-defined nano-objects similar to those produced with non-reactive monomers (e.g. benzyl methacrylate) and to retain morphologies independent of solvent and temperature.
In this work the structural differences in binary latex composites are investigated, with a particular focus on the effect of changing size ratio. It is demonstrated that, in composites cast from low and high Tg latex dispersions, stratified layers of the smaller species may be present in the dry composite. It is highlighted that, stratification is heavily influenced by changing the size ratio of the two latex species, with smaller particles able to stratify at lower volume fractions relative to the larger species. It is also demonstrated that, stratification is less likely in composites cast from more highly concentrated dispersions. In the case of composites cast from more concentrated dispersions, stratification is only observed in films with a high size ratio and high volume fraction of the small species.
The tensile properties of the same composites were investigated in films with soft/hard size ratios of 1:1 and 7:1. Two distinct routes to brittleness, as the volume fraction of hard particles are increased, are identified. A 1:1 size ratio leads to a sharp transition from ductile to brittle, whereas a 7:1 size ratio leads to a more gradual decline from ductile to brittle. The proposed reason for the two distinct routes is a structural one, in which the microstructure of the binary composites prevents continuity of the low Tg phase to varying extends depending on both volume fraction and size ratio.
The structural investigation of binary composites is advanced by investigating the structures and mechanical properties of latex/calcium carbonate composites over a range of size ratios, incorporating sizes of filler particles from nano-sized to micro-sized. It is demonstrated that smaller filler particles lead to the onset of brittleness at lower volume fractions than larger ones, however smaller particles also provide greater mechanical reinforcement at lower volume fractions in latex/calcium carbonate composites.
The isothermal structural relaxation of glassy, spin-cast polymer thin films has been investigated. Specifically, the thickness h of freshly cast poly(methyl methacrylate) thin films was measured over time using spectroscopic ellipsometry. The spin-cast films exhibit a gradual decrease in thickness, which is attributed to structural relaxation of the glass combined with simultaneous solvent loss. In all cases, It was found to be greater than the equilibrium thickness h(infinity), which is obtained by cooling slowly from the melt. It is observed that both the rate of the volume relaxation and the fractional departure from h. (referred to as delta(0)) increase with increasing film thickness. In the limit of very thin films, the initial h is close to h(infinity), and delta(0) is small, whereas in thick films (>500 nm), a plateau value of delta(0) of 0.16 is observed, which is close to the volume fraction of the solvent at the vitrification point. This dependence of) on thickness is observed regardless of the substrate, polymer molecular weight, or angular velocity during spin casting. Enhanced mobility near film surfaces could be leading to greater relaxation in thinner films prior to, and immediately after, the vitrification of the polymer during the deposition process.
For a wide range of applications, films are deposited from colloidal particles suspended in a volatile liquid. There is burgeoning interest in stratifying colloidal particles into separate layers within the final dry film to impart properties at the surface different to the interior. Here, we outline the mechanisms by which colloidal mixtures can stratify during the drying process. The problem is considered here as a three-way competition between evaporation of the continuous liquid, sedimentation of particles, and their Brownian diffusion. In particle mixtures, the sedimentation of larger or denser particles offers one means of stratification. When the rate of evaporation is fast relative to diffusion, binary mixtures of large and small particles can stratify with small particles on the top, according to physical models and computer simulations. We compare experimental results found in the scientific literature to the predictions of several recent models in a quantitative way. Although there is not perfect agreement between them, some general trends emerge in the experiments, simulations and models. The stratification of small particles on the top of a film is favoured when the colloidal suspension is dilute but when both the concentration of the small particles and the solvent evaporation rate are sufficiently high. A higher ratio also favours stratification by size. This review points to ways that microstructures can be designed and controlled in colloidal materials to achieve desired properties.
Nanoparticles of cerium dioxide (or nanoceria) are of interest because of their oxygen buffering, photocatalytic ability, and high UV absorption. For applications, the nanoceria can be incorporated in a polymer binder, but questions remain about the link between the nanoparticle distribution and the resulting nanocomposite properties. Here, the thermal, mechanical and optical properties of polymer/ceria nanocomposites are correlated with their nanostructures. Specifically, nanocomposites made from waterborne Pickering particles with nanoceria shells are compared to nanocomposites made from blending the equivalent surfactant-free copolymer particles with nanoceria. Two types of nanoceria (protonated or citric acid-coated) are compared in the Pickering particles. A higher surface coverage is obtained with the protonated ceria, which results in a distinct cellular structure with nanoceria walls within the nanocomposite. In the blend of particles, a strong attraction between the protonated nanoceria and the acrylic acid groups of the copolymer likewise leads to a cellular structure. This structure offers transparency in the visible region combined with strong UV absorption, which is desired for UV blocking coating applications. Not having an attraction to the polymer, the citric acid-coated nanoceria forms agglomerates that lead to undesirable light scattering in the nanocomposite and yellowing. This latter type of nanocomposite coating is less effective in protecting substrates from UV damage but provides a better barrier to water. This work shows how the nanoparticle chemical functionalization can be used to manipulate the structure and to tailor the properties of UV-absorbing barrier coatings.
Water-borne and emulsifier-free coatings have attracted academic and industrial interests because they are environmentally-friendly. The water barrier properties are being developed, but it is hypothesized that removal of surfactant will improve the barrier properties. In this work, water transport and sorption in acrylate copolymer coatings deposited from colloidal dispersions (emulsion polymers and secondary emulsion polymers) and from solution in an organic solvent were investigated in order to compare the water transport and sorption for the different materials and to identify the important factors, including the presence of boundaries between particles and the presence of surfactants.
Solution polymer films were found to have no particle boundaries and to be more homogenous in structure compared to the other types of films. They sorbed the least amount of water from both vapour and liquid. Secondary emulsion polymer films sorbed less amount of water than the emulsion polymer films of similar chemical composition. It was found that the increase of sorbed water content in the emulsion films can be ascribed to the hydrophilic nature of the surfactants that stay at the particle boundaries, enabling the water transport. Hence, after being dialyzed, the emulsion polymer films were found to adsorb more water, probably due to poor film formation (particle coalescence). It was concluded that dissolving the particle boundaries in emulsion polymer films (by casting from organic solvent) reduced the uptake of water. We used the technique of NMR relaxometry to find that there were three 1H peaks in the different regions of the T2 spectra for films after soaking in water. These three peaks correspond to different environments: molecularly dissolved water (and mobile polymer); interfacial water; and water in voids or channels. It was found that the water environment and the extent of confinement correlate with the optical transmission through the film. A greater volume fraction of scatterers (mobile water in voids or pockets) and larger scatterers led to a loss of the optical transparency that is usually not desired in coatings applications.
The water vapour diffusion through all of the films was Fickian, as indicated by a sufficient regression to the experimental data over a series of water activities ranging from 0 to 0.9. In all cases, the diffusion coefficients (D) decreased with increasing water activities. The D seemed to have marginal differences between the various samples, indicating the removal of boundaries has limited effects. D is more strongly dependent on the water activities, and hence also on the sorbed water content. Without surfactants, a smaller diffusion coefficient was found for the secondary emulsion film. This result means that the presence of surfactant speeds the diffusion of water vapour molecules. Comparing the water uptake results, the equilibrium sorption of water vapour (100 % RH) and liquid water show only small differences.
We also used Rutherford backscattering spectrometry (RBS) to investigate the transport of ions through various films. The diffusion of ions into the emulsion and solution films can be described using the theory of Fickian dynamics. The solvent-borne films had a slow diffusion of ions, and the surface concentration was lower. A higher atomic surface concentration was observed in the emulsion film, possibly due to an ion exchange with the counter-ions that balance the negative charges (e.g. SO3-, NH4+) of surfactants in situ.