Constantina (Tina) Lekakou

Professor Constantina (Tina) Lekakou

Professor in Energy, Multiphase and Multifunctional Materials and Devices
PhD (Imperial College), Dipl. Chemical Eng. (NTUA), CEng, MIMechE

Academic and research departments

School of Mechanical Engineering Sciences.


Areas of specialism

Energy materials, devices and systems; Functional and biomedical materials; Smart and actuating materials and their modelling for robotic applications; Multiphase and composite materials science and engineering

University roles and responsibilities

  • Organiser of the Individual Final Year Projects (BEng and MEng)
  • Member of the Academic Misconduct Panels

    Affiliations and memberships

    Chartered Engineer, UK
    Institute of Mechanical Engineers, UK
    Technical Chamber of Greece (TEE-TCG)
    Institute of Chemical Engineers, Greece
    European Society of Composite Materials (ESCM)
    International Association of Engineers (IAENG)
    Materials KTN
    EPSRC UK-RAS Network
    Energy Storage Research Network, UK



    Research interests

    Research projects

    Indicators of esteem

    • IOM3 AWARDS 2020: AWARDS FOR PUBLISHED WORK - Composite Award: Mathew Rutt, Constantina (Tina) Lekakou, Paul A Smith, Alessandro Sordon and Ian Hamerton received the Composite Award from IoM3 for their published paper: "Methods for process-related resin selection and optimisation in high-pressure resin transfer moulding" published in Materials Science and Technology, 35(3), 2018, pp.327-335.

    • Invited Keynote Speaker at 3rd International Conference on Materials Science and Materials Chemistry (ICMSMC19), Vienna, 14-15 Oct 2019, Talk titled: “Materials for post Li-ion batteries”

    • As overall coordinator of the EC-funded research project AUTOSUPERCAP, C.Lekakou received Best Prize in the FP7 NMP projects (2007-2014) ongoing category, awarded by the European Community (EC)  (April 2014).

    • Patent GB201509870D0 “Composite Supercapacitor”, Assignee University of Surrey, 2015-07-22 Grant.

    • Best Paper Award at the 2007 International Conference of Mechanical Engineering in World Congress of Engineering WCE 2007 for the paper: U. Vidyarthi, P. Zhdan, C. Gravanis and C. Lekakou "Gelatine-hydroxyapatite nanocomposites for orthopaedic applications".

    • Panellist in Panel Discussion at TAROS2017 (18th Annual Conference Towards Autonomous Robotic Systems, 2017, Guildford) with Professor Yang Gao, Surrey Space Centre, Professor Alan Winfield, UWE Bristol, Dr Alexander Thorn, University of Sheffield.

    • Invited Speaker at NARA Institute of Science and Technology (NAIST), Japan, Summer 2016.

    • Panellist in Panel Discussion at ICRA 2014 Workshop: Soft and stiffness-controllable robots for MIS, 1st June 2014, Hong Kong, IEEE Robotics and Automation Society.

    • Invited Speaker to Experts Workshops of ICT4EV in Brussels (Nov 2010), Berlin (June 2011), Brussels (April 2013; December 2014).

    • Invited Speaker/Plenary Session at IEEE-NANO: C. Lekakou, C. Lei, F. Markoulidis, A. Sorniotti “Nanomaterials and Nanocomposites for High Energy/High Power Supercapacitors” IEEE 12th International Conference on Nanotechnology (IEEE-NANO), August 2012.

    • Editor of Lecture Notes in Computer Science book series (LNCS, volume 10454), 2017, Editors: Y. Gao, S. Fallah, Y. Jin, C. Lekakou, Publisher: Springer.

    • Member of the Editorial Board of Advances in Mechanical Engineering, Publisher: SAGE (2018-present)

    • Member of the Editorial Board of the Journal of Composites Science, Publisher: MDPI (2016-present).

    • Member of the Editorial Board for the SF Journal of Biotechnology and Biomedical Engineering (2018-present).

    • Associate Editor for journal: Advances in Renewable Energy, Avestia Publishers (2013-2017).



    Selected publications from the last 10 years

    R. Reece, C. Lekakou, P.A. Smith ""A High-Performance Structural Supercapacitor""  ACS Appl. Mater. Interfaces 2020, 12, 23, 25683–25692

    F. Markoulidis, J. Bates, C. Lekakou, R. Slade, G.M. Laudone “Supercapacitors with lithium-ion electrolyte: An experimental study and design of the activated carbon electrodes via modelling and simulations” Carbon, 2020, online:

    R. Reece, C. Lekakou, P.A. Smith, R. Grilli, C. Trapalis “Sulphur-linked graphitic and graphene oxide platelet-based electrodes for electrochemical double layer capacitors” Journal of Alloys and Compounds, 792, 2019, pp.582-593

    Jonathan Pope and Constantina (Tina) Lekakou “Thermoelectric polymer composite yarns and an energy harvesting wearable textile” Smart Materials and Structures, published online 2019

    Y. Elsayed  C. Lekakou  P. Tomlins “Modeling, simulations, and optimization of smooth muscle cell tissue engineering for the production of vascular grafts” Biotechnology and Bioengineering, online 2019,

    S.Mastura Mustaza, Y.Elsayed, C.Lekakou , C.Saaj, J.Fras “Dynamic modeling of fiber-reinforced soft manipulator: A Visco-hyperelastic material-based continuum mechanics approach” Soft Robotics, online March 2019,

    M.Rutt, C.Lekakou, P.A.Smith, A.Sordon, C.Santoni, G.Meeks & I.Hamerton “Methods for process-related resin selection and optimisation in high-pressure resin transfer moulding” Materials Science and Technology, 35(3), 2018, pp.327-335. IoM3 Composite Award

    R.Reece, C.Lekakou, P.A.Smith “A structural supercapacitor based on activated carbon fabric and a solid electrolyte” Materials Science and Technology, 35(3), 2018, pp.368-375

    E. Shumbayawonda, A.A.Salifu, C.Lekakou, J.P.Cosmas “Numerical and Experimental Simulations of the Wireless Energy Transmission and Harvesting by a Camera Pill” ASME Transactions - Journal of Medical Devices, 12, 2018, doi:10.1115/1.4039390, 9pp.

    E.C. Vermisoglou, T. Giannakopoulou, G. Romanos, N. Boukos, V. Psycharis, C. Lei, C. Lekakou, D. Petridis and C. Trapalis “Graphene-based materials via benzidine-assisted exfoliation and reduction of graphite oxide and their electrochemical properties” Applied Surface Science, 392, 2017, 244-255

    N. Todorova, T. Giannakopoulou, N. Boukos, E. Vermisoglou, C. Lekakou, C. Trapalis “Self-propagating solar light reduction of graphite oxide in water” Applied Surface Science, Part B, 391, 2017, pp.601-608

    R.Fields, C.Lei, F.Markoulidis and C.Lekakou “The Composite Supercapacitor” Energy Technology, 4(4), 2016, pp. 517–525

    A.A. Salifu, C. Lekakou, F. Labeed “Multilayer cellular stacks of gelatin-hydroxyapatite fiber scaffolds for bone tissue engineering”, Journal of Biomedical Materials Research Part A, 105(3), 2017, pp. 779-789

    A.A. Salifu, C. Lekakou, F.H. Labeed “Electrospun oriented gelatin-hydroxyapatite fiber scaffolds for bone tissue engineering”, Journal of Biomedical Materials Research Part A, 105(7), 2017, pp. 1911–1926

    Y.Elsayed,  C.Lekakou, F.Labeed, and P.Tomlins “Fabrication and characterisation of biomimetic, electrospun gelatin fibre scaffolds for tunica media-equivalent, tissue engineered vascular grafts” Materials Science & Engineering C-Materials For Biological Applications, 61, 2016, pp. 473-483

    Y.Elsayed,  C.Lekakou, F.Labeed, and P.Tomlins “Smooth muscle tissue engineering in crosslinked electrospun gelatin scaffolds” Journal of Biomedical Materials Research Part A, 104(1), 2016, pp.313–321

    C.Lei, F.Markoulidis, P.Wilson and C.Lekakou “Phenolic Carbon Cloth-Based Electric Double-Layer Capacitors with Conductive Interlayers and Graphene Coating” Journal of Applied Electrochemistry, 46(2), 2016, pp.251–258

    E.C.Vermisoglou, T.Giannakopoulou, G.E.Romanos, N.Boukos, M.Giannouri, C.Lei, C. Lekakou and C.Trapalis “Non-Activated High Surface Area Expanded Graphite Oxide for Supercapacitors” Applied Surface Science, Part A, 358, 2015, pp.110-121

    E.C. Vermisoglou, T. Giannakopoulou, G. Romanos, M. Giannouri, N. Boukos, C. Lei,C. Lekakou, C. Trapalis “Effect of hydrothermal reaction time and alkaline conditions on the electrochemical properties of reduced graphene oxide” Applied Surface Science, Part A, 358, 2015, pp.100-109

    I.Papailias, M. Giannouri, A. Trapalis, N.Todorova, T. Giannakopoulou, N. Boukos, C. Lekakou “Decoration of crumpled rGO sheets with Ag nanoparticles by spray pyrolysis” Applied Surface Science, Part A, 358,  2015, pp.84-90

    C.Lekakou, Y. Elsayed, T. Geng and C.M. Saaj “Skins and Sleeves for Soft Robotics: Inspiration from Nature and Architecture” Advanced Engineering Materials, 17(8), 2015, pp. 1180-1188

    Y.Elsayed, C.Lekakou, T. Ranzani, M.Cianchetti, M Morino, A.Arezzo, A.Menciassi, T.Geng and C.M.Saaj “Crimped braided sleeves for soft, actuating arm in robotic abdominal surgery”, Minimally Invasive Therapy & Allied Technologies, 24(4), 2015, pp. 204-210

    Y Elsayed,  A Vincensi, C Lekakou, T Geng,, C. M. Saaj, T Ranzani, M Cianchetti,and A Menciassi “Finite Element Analysis and Design Optimization of a Pneumatically Actuating Silicone Module for Robotic Surgery Applications”, Soft Robotics, 1(4), 2014, pp. 255-262

    F.Markoulidis, C.Lei, C. Lekakou, D.Duff, S.Khalil, B.Martorana and I.Cannavaro “A Method to Increase the Energy Density of Supercapacitor Cells by the Addition of Multiwall Carbon Nanotubes into Activated Carbon Electrodes” Carbon, 68, 2014, pp.58–66

    E.C.Vermisoglou, E.Devlin, T.Giannakopoulou, G.Romanos, N.Boukos, V.Psycharis, C.Lei, C.Lekakou, D.Petridis and C. Trapalis “Reduced Graphene Oxide/Iron Carbide Nanocomposites for Magnetic and Supercapacitor Applications” Journal of Alloys and Compounds, 590, 2014, pp.102-109

    A. Santucci, A. Sorniotti and C. Lekakou “Power split strategies for hybrid energy storage systems for vehicular applications” Journal of Power Sources, 258, 2014, pp.395-407

    P Wilson, C.Lei, C Lekakou, JF Watts “Transverse charge transport in inkjet printed poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS)”, Organic Electronics, 15(9), 2014, pp. 2043-2051

    P.Wilson, C.Lekakou and J.F.Watts “In-plane conduction characterisation and charge transport model of DMSO co-doped, inkjet printed Poly(3,4-ethylenedioxythiophene): Polystyrene sulfonate (PEDOT:PSS)”, Organic Electronics, 14, 2013, pp.3277–3285

    Y.Elsayed,  C.Lekakou, P.Tomlins “Monitoring and modelling of oxygen transport through un-crosslinked and crosslinked gelatine gels”, Polymer Testing, 40, 2014, pp.106-115

    F.Markoulidis, C.Lei, C.Lekakou “Fabrication of high-performance supercapacitors based on transversely oriented carbon nanotubes”. Applied Physics A: Materials Science and Processing, 111 (1), 2013, pp. 227-236

    C. Lei, F. Markoulidis, Z. Ashitaka and C. Lekakou “Reduction of porous carbon/Al contact resistance for an electric double-layer capacitor (EDLC)” Electrochimica Acta, 92, 2013, pp.183– 187

    C. Lei, N. Amini, F. Markoulidis, P. Wilson, S. Tennison and C. Lekakou “Activated carbon from phenolic resin with controlled mesoporosity for an electric double-layer capacitor (EDLC)” Journal of Materials Chemistry A, 1(19), 2013, pp. 6037-6042

    P.Wilson, C.Lekakou, J.F.Watts “A comparative assessment of surface microstructure and electrical conductivity dependence on co-solvent addition in spin coated and inkjet printed poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS), Organic Electronics, 13 (3), 2012, pp.409 – 418

    C.Lei, P.Wilson, C.Lekakou “Effect of poly(3,4-ethylenedioxythiophene) (PEDOT) in carbon-based composite electrodes for electrochemical supercapacitors” Journal of Power Sources, 196 (18), 2011, pp. 7823-7827

    A.A.Salifu, B.D.Nury and C.Lekakou "Electrospinning of nanocomposite fibrillar tubular and flat scaffolds with controlled fiber orientation" Annals of Biomedical Engineering, 39(10), 2011, 2510-2520

    A.K.Murugesh, A.Uthayanan and C.Lekakou "Electrophoresis and orientation of multiple wall carbon nanotubes in polymer solution", Applied Physics A:  Materials Science and Processing, 100(1), 2010, pp.135-144

    C.Lekakou, D.Lamprou, U.Vidyarthi, E.Karopoulou and P.Zhdan "Structural hierarchy of biomimetic materials for tissue engineered vascular and orthopaedic grafts" Journal of Biomedical Materials Research Part B-Applied Biomaterials Volume: 85B   Issue: 2   Pages: 461-468   Published: 2008, pp.461-468 

    Roby Soni, Damiano Spadoni, Paul R. Shearing, Dan J. L. Brett, Constantina Lekakou, Qiong Cai, James B. Robinson, Thomas S. Miller (2023)Deploying Proteins as Electrolyte Additives in Li-S Batteries: The Multifunctional Role of Fibroin in Improving Cell Performance, In: ACS applied energy materials6(11)pp. 5671-5680 American Chemical Society

    It is widely accepted that the commercial application of lithium–sulfur batteries is inhibited by their short cycle life, which is primarily caused by a combination of Li dendrite formation and active material loss due to polysulfide shuttling. Unfortunately, while numerous approaches to overcome these problems have been reported, most are unscalable and hence further hinder Li–S battery commercialization. Most approaches suggested also only tackle one of the primary mechanisms of cell degradation and failure. Here, we demonstrate that the use of a simple protein, fibroin, as an electrolyte additive can both prevent Li dendrite formation and minimize active material loss to enable high capacity and long cycle life (up to 500 cycles) in Li–S batteries, without inhibiting the rate performance of the cell. Through a combination of experiments and molecular dynamics (MD) simulations, it is demonstrated that the fibroin plays a dual role, both binding to polysulfides to hinder their transport from the cathode and passivating the Li anode to minimize dendrite nucleation and growth. Most importantly, as fibroin is inexpensive and can be simply introduced to the cell via the electrolyte, this work offers a route toward practical industrial applications of a viable Li–S battery system.

    Foivos Markoulidis, Josh Bates, Constantina Lekakou, Bob Slade, Guliano M. Laudone (2020)Supercapacitors with lithium-ion electrolyte: An experimental study and design of the activated carbon electrodes via modelling and simulations, In: Carbon Elsevier

    Electrochemical double layer capacitors (EDLCs) are investigated with activated carbon electrodes and a lithium-ion electrolyte, in anticipation of potential future applications in hybridised battery-supercapacitor devices and lithium ion capacitors. An experimental study of a symmetric electrochemical double layer capacitor (EDLC) with activated carbon (AC) electrodes on aluminium foil current collectors and electrolyte 1 M LiPF6 in EC:EMC 50:50 v/v concludes a stability window to a maximum potential of 3 V, an equivalent in series resistance of 48 ohm for 1 cm2 cell area (including the contact resistance between electrode and current collector) and an average specific electrode capacitance of 50.5 F g-1. Three AC electrode materials are assessed via computer simulations based on a continuum ion and charge transport model with volume-averaged equations, considering the pore size distribution for each electrode material and, depending on pore size, transport of tetrahedral solvated or flat solvated Li+ ions and solvated or desolvated PF6- ions. The computer simulations demonstrate that the best electrode material is an AC coating electrode with a hierarchical pore size distribution measured in the range of 0.5-180 nm and bimodal shape, and specific surface area BET = 808 m2 g-1.

    Joseph Paul Baboo, Ewa Jakubczyk, Mudasir A. Yatoo, Matthew Phillips, Sean Grabe, Matthew Dent, Steven J. Hinder, John F. Watts, Constantina Lekakou (2023)Investigating battery-supercapacitor material hybrid configurations in energy storage device cycling at 0.1 to 10C rate, In: Journal of power sources561 Elsevier

    Battery-supercapacitor hybridisation enables safe charge-discharge operation at high C rate, up to the supercapacitor capacity, while maintaining battery lifetime. However, battery-supercapacitor systems in parallel connection require a DC/DC converter for voltage balance. Hybridisation at material level is explored in this study aiming to avoid the use of a DC/DC converter. Different battery-supercapacitor configurations, hybridised at material level, are investigated with the goal to maintain the long redox plateau of the battery and to self-balance without the need of DC/DC converter. Applying these principles to a LiFePO4 (LFP) battery, the best configuration was found to be a device with a Li anode and a composite LFP/activated carbon (AC) cathode reaching 180 mAh per gram of battery cathode. The device is cycled according to different schedules from 0.1C to 10C rate and the cathode and anode surface are characterised microstructurally and in terms of their chemical composition, after just fabricated and post-mortem after cycling according to different C rate schedules.

    James B Robinson, Kai Xi, Vasant Kumar, Andrea C Ferrari, Heather Au, Maria-Magdalena Titirici, Andres Parra-Puerto, Anthony R Kucernak, Samuel D S Fitch, Nuria Garcia-Araez, Zachary L Brown, Mauro Pasta, Liam Furness, Alexander J Kibler, Darren A Walsh, Lee R Johnson, Conrad Holc, Graham N Newton, Neil R Champness, Foivos Markoulidis, Carol Crean, Robert C T Slade, Eleftherios I Andritsos, Qiong Cai, Shumaila Babar, Teng Zhang, Constantina Lekakou, Nivedita Kulkarni, Alexander J E Rettie, Rhodri Jervis, Michael Cornish, Monica Marinescu, Gregory Offer, Zhuangnan Li, Liam Bird, Clare P Grey, Manish Chhowalla, Daniele Di Lecce, Rhodri E Owen, Thomas S Miller, Dan J L Brett, Sebastien Liatard, David Ainsworth, Paul R Shearing (2022)2021 roadmap on lithium sulfur batteries, In: JPhys Energy3(3)031501 IOP Publishing

    Batteries that extend performance beyond the intrinsic limits of Li-ion batteries are among the most important developments required to continue the revolution promised by electrochemical devices. Of these next-generation batteries, lithium sulfur (Li–S) chemistry is among the most commercially mature, with cells offering a substantial increase in gravimetric energy density, reduced costs and improved safety prospects. However, there remain outstanding issues to advance the commercial prospects of the technology and benefit from the economies of scale felt by Li-ion cells, including improving both the rate performance and longevity of cells. To address these challenges, the Faraday Institution, the UK's independent institute for electrochemical energy storage science and technology, launched the Lithium Sulfur Technology Accelerator (LiSTAR) programme in October 2019. This Roadmap, authored by researchers and partners of the LiSTAR programme, is intended to highlight the outstanding issues that must be addressed and provide an insight into the pathways towards solving them adopted by the LiSTAR consortium. In compiling this Roadmap we hope to aid the development of the wider Li–S research community, providing a guide for academia, industry, government and funding agencies in this important and rapidly developing research space.

    George Ntanovasilis, Ioannis Zaverdas, Tarig Ahmed, FOIVOS MARKOULIDIS, Constantina Lekakou (2021)Polymer blends and polymer nanocomposites for photovoltaic (Pv) cells and an investigation of the material deposition techniques in pv cell fabrication, In: Journal of composites science5(10)263 Mdpi

    Polymer photovoltaics (PV) offer the advantage of low-cost, mass-produced, flexible PV films, but they generally suffer from a low-power conversion efficiency (PCE) compared to silicon. This paper studies ITO/PEDOT:PSS/bulk heterojunction/Al PV cells, where two different bulk heterojunction blends are researched: P3HT/PC61BM and PCDTBT/PC70BM. The addition of multiwall carbon nanotubes (CNT) is explored as a conductive network to accelerate the electron transport and extraction to the outer aluminium current collector while reducing the chance of charge recombinations. Several layer deposition techniques are investigated: spin coating and casting, as well as techniques that would induce transverse orientation of polymer grains, including inkjet printing, electrophoresis and the application of a transverse AC field during annealing. Transverse orientation techniques produced architectures that would facilitate charge transport without recombinations, but it is recommended to avoid such techniques for the deposition of conductive PEDOT:PSS and CNT layers as they create a high surface roughness that leads to short circuiting. The best performing PV cell is the ITO/PEDOT:PSS/PCDTBT/PC70BM/CNT/Al structure with a PCE of 11%.

    Hakeem A. A. Adeoye, Matthew Joseph Dent, John Farnham Watts, Stephen Robert Tennison, Constantina Lekakou (2023)Solubility and dissolution kinetics of sulfur and sulfides in electrolyte solvents for lithium-sulfur and sodium-sulfur batteries, In: The Journal of Chemical Physics158(6)064702 AIP Publishing

    In this study, we monitor the dissolution of sulfur and sulfides in electrolyte solvents for lithium-sulfur (Li-S) and sodium-sulfur (Na-S) batteries. The first aim of this research is to assemble a comprehensive set of data on solubilities and dissolution kinetics that may be used in the simulation of battery cycling. The investigation also offers important insights to address key bottlenecks in the development and commercialization of metal-sulfur batteries, including the incomplete dissolution of sulfur in discharge and insoluble low-order sulfides in charge, the probability of shuttling of soluble polysulfides, and the pausing of the redox reactions in precipitated low order sulfides depending on their degree of solid state. The tested materials include sulfur, lithium sulfides Li2Sx, x = 1, 2, 4, 6, and 8, and sodium sulfides Na2Sx, x = 1, 2, 3, 4, 6, and 8, dissolved in two alternative electrolyte solvents: DOL:DME 1:1 v/v and TEGDME. The determined properties of the solute dissolution in the solvent include saturation concentration, mass transfer coefficient, and diffusion coefficient of the solvent in the solid solute. In general, the DOL:DME system offers high solubility in Li-S batteries and TEGDME offers the highest solubility in Na-S batteries. Low solubility sulfides are Li2S2 and Li2S for the Li-S batteries, and Na2S3, Na2S2, and Na2S for the Na-S batteries. However, it is noted that Na2S3 dissolves fast in TEGDME and also TEGDME diffuses fast into Na2S3, offering the possibility of a swollen Na2S3 structure in which Na+ ions might diffuse and continue the redox reactions in a semisolid state.

    Sean Grabe, Joseph Paul Baboo, Stephen Tennison, Teng Zhang, Eleftherios I Andritsos, Qiong Cai, Stephen Downes, Stephen Hinder, John F. Watts, Constantina Lekakou (2022)Sulfur infiltration and allotrope formation in porous cathode hosts for lithium-sulfur batteries, In: AIChE journal68(7)e17638 Wiley

    We investigate sulfur infiltration and formation of lower order allotropes in heated porous hosts during fabrication of lithium-sulfur (Li-S) battery cathodes. Sulfur existence in cathode ultramicropores has been an important question for Li-S batteries, as ultramicropores reduce the polysulfides " shuttle effect " but also delay sulfur dissolution and Li + ion diffusion in the trapped solid sulfur. A novel continuum-level model is presented including heat transfer and sulfur infiltration, either from the top of a porous host or from the porous host particle surface, and taking into account the pore size distribution. A novel decay factor in modeling sulfur infiltration incorporates the pore wall repulsion energy and allotrope formation energy (predicted by density functional theory [DFT] simulations). Simulations are performed for a microporous carbon fabric host and an activated carbon powder host with bimodal micropore and macropore size distribution , with Raman and X-ray photoemission spectroscopy (XPS) spectroscopy confirming the predicted existence of linear S 6 and S 4 in ultramicropores. K E Y W O R D S lithium-sulfur batteries, melt and vapor infiltration, pore size distribution in cathode, sulfur allotropes 1 | INTRODUCTION Lithium-sulfur (Li-S) batteries have been in the research focus in the last decade because of their high theoretical energy density, 2510 Wh kg À1 , abundance and low toxicity of sulfur. 1 Intensive effort has been devoted on the cathode, where sulfur is incorporated in a porous conductive host with the aim for the host to not only enhance electronic conductivity but also allow for cathode expansion on the insertion of Li + ions and formation of polysulfides Li 2 S x during discharge. 2 Additionally, effective cathode hosts offer means to trap the sulfur and polysulfides to limit polysulfide shuttling between cathode and anode, which would cause reduction in capacity and coulombic efficiency. 3,4 Suitable microstructural architectures, including small pores, pores with necks and hollow particles, 5,6 and hosts functionalized with chemical groups with high adsorption energy to sulfur and sulfides 7 can provide such good traps. Additional specifications for host porosity and pore size distribution (PSD) target a sulfur mass greater than 5 mg cm À2 , making up at least 70% of the cathode weight, to realize the high theoretical energy density of Li-S batteries. 8 There is a vast range of porous host material candidates for Li-S battery cathodes: porous carbons, 5,6,9 activated carbon (AC) fabrics or fibers, 10,11 graphene and graphene oxide, 12–15 and

    ELEFTHERIOS ANDRITSOS, CONSTANTINA LEKAKOU, QIONG CAI (2021)Single-Atom Catalysts as Promising Cathode Materials for Lithium-Sulfur Batteries, In: Journal of physical chemistry. C125(33)pp. 18108-18118 American Chemical Society
    Matthew Joseph Dent, Ewa Monika Jakubczyk, Teng Zhang, Constantina Lekakou (2022)Kinetics of sulphur dissolution in lithium-sulphur batteries, In: JPhys Energy4(2)24001 IOP Publishing

    This study investigates and determines the dissolution kinetics of solid sulphur in DOL:DME solution, a typical electrolyte solution for lithium-sulphur (Li-S) batteries, at four different temperatures, in the range of 17 degrees C-20 degrees C. The dissolution kinetics is considered as a function of the solid sulphur-solution interfacial area. The analysis yielded fast dissolution kinetics with a mass transfer coefficient of 2.3 x 10(-3) m s(-1) at 20 degrees C but low sulphur solubility of 0.058 S mol lt(-1), with the latter being a limiting factor in sulphur dissolution. In later stages, swelling of the solid sulphur region was also observed as a function of time from which the diffusion coefficient of the DOL:DME solution in the solid sulphur was determined. A novel model for the sulphur dissolution and electrolyte impregnation in a Li-S cathode in battery fabrication is presented taking into account the pore size distribution of the cathode host. A computer simulation was carried out and the model and the dissolution parameter values were validated by comparing the predictions with experimental data from in operando microscopy during the dissolution of sulphur and infiltration of the DOL:DME solution in a commercial sulphur-conductive carbon cathode.

    Sean Grabe, Matthew Dent, Shumaila Babar, Teng Zhang, Stephen Tennison, John F Watts, Constantina Lekakou (2023)Investigation and Determination of Electrochemical Reaction Kinetics in Lithium-Sulfur Batteries with Electrolyte LiTFSI in DOL/DME, In: Journal of the Electrochemical Society170(2) Electrochemical Soc Inc

    A major challenge in the simulation of Li-S batteries is that the electrochemical reaction parameters supplied from the fitting of 0-d or 1-d models depend on the cathode and separator microstructure, so these parameters cannot be used in the design and optimization of material microstructure. The present investigation fits the electrochemical reaction kinetics employing a continuum model taking into account the pore size distribution and tortuosity of cathode and separator in the transport of sulfur molecules and ion species (Li+ ion, electrolyte and sulfide anions) in solvated or desolvated form depending on pore size. Hence, the specified reaction kinetics parameters are independent from the material microstructure. The Li-S redox reaction model includes six redox reactions in the cathode and the lithium redox reaction at the anode. Reactions are assumed to take place in the electrolyte solution rather than in the solid phase of sulfur or lithium sulfide precipitates, where dissolution/precipitation kinetics is modeled especially for the low solubility compounds: sulfur, Li2S and Li2S2. The fitting exercise is conducted based on experimental data of a cyclic voltammetry cycle accompanied by in operando UV-vis spectroscopy. The investigated battery has electrolyte LiTFSI in DOL/DME and no electrocatalysts in any part of the cell.

    Joseph Paul Baboo, Mudasir A. Yatoo, Matthew Dent, Elaheh Hojaji Najafabadi, Constantina Lekakou, Robert Slade, Steven J. Hinder, John F. Watts (2022)Exploring Different Binders for a LiFePO4 Battery, Battery Testing, Modeling and Simulations, In: Energies (Basel)15(7) Mdpi

    This paper focuses on the LiFePO4 (LFP) battery, a classical and one of the safest Li-ion battery technologies. To facilitate and make the cathode manufacture more sustainable, two Kynar (R) binders (Arkema, France) are investigated which are soluble in solvents with lower boiling points than the usual solvent for the classical PVDF binder. Li-LFP and graphite-Li half cells and graphite-LFP full cells are fabricated and tested in electrochemical impedance spectroscopy, cyclic voltammetry (CV) and galvanostatic charge-discharge cycling. The diffusion coefficients are determined from the CV plots, employing the Rendles-Shevchik equation, for the LFP electrodes with the three investigated binders and the graphite anode, and used as input data in simulations based on the single-particle model. Microstructural and surface composition characterization is performed on the LFP cathodes, pre-cycling and after 25 cycles, revealing the aging effects of SEI formation, loss of active lithium, surface cracking and fragmentation. In simulations of battery cycling, the single particle model is compared with an equivalent circuit model, concluding that the latter is more accurate to predict "future" cycles and the lifetime of the LFP battery by easily adjusting some of the model parameters as a function of the number of cycles on the basis of historical data of cell cycling.

    Shumaila Babar, Constantina Lekakou (2021)Molecular modeling of electrolyte and polysulfide ions for lithium-sulfur batteries, In: Ionics27(2)pp. 635-642 Springer Berlin Heidelberg

    The operation of a lithium-sulfur (Li-S) battery involves the transport of Li + ions and soluble sulfides mostly in the form of solvated ions. Key challenges in the development of Li-S battery technology are the diffusion of Li + in micropores filled with sulfur and eliminating the “shuttling” of polysulfides. Ion dimensions in solvated and desolvated forms are key parameters determining the diffusion coefficient and the rate of transport of such ions, while constrictivity effects due to the effect of pore size compared to ion size control both transport and filling of the pores. We present molecular simulations to determine the solvation parameters of electrolyte ions and sulfides S 2 2− , S 4 2− , S 6 2− , and S 8 2− in two different electrolyte systems: LiTFSI in DOL/DME and LiPF 6 in EC/DMC. The calculated parameters include the coordination number and the geometrically optimized model and dimensions, using the van der Waals surface approach, of the solvated and desolvated ions. The desolvation energy of the electrolyte ions is also calculated. Such data is useful for the modeling and design of the pore sizes of cathode host materials to be able to accommodate the different sulfides while minimizing their “shuttling” between cathode and anode.

    Chunhong Lei, Richard Fields, Peter Wilson, Constantina Lekakou, Negar Amini, Stephen Tennison, John Perry, Michele Gosso, Brunetto Martorana (2020)Development and evaluation of a composite supercapacitor-based 12 V transient start–stop power system for vehicles: Modelling, design and fabrication scaling up, In: Proceedings of the Institution of Mechanical Engineers, Part A: Journal of Power and Energy SAGE Publications

    The study involves a bottom-up approach, from bottom cells to large supercapacitor pouch cells, encompassing the design, modelling and fabrication stages of the cells leading to a 12 V transient start-stop (TSS) power system for automotive applications. More specifically, the design of a large composite supercapacitor is presented, consisting of a high power density component and a high energy density component, hybridised at material level. The composition of the composite supercapacitor is optimised to be application-specific so that it satisfies a specified energy-to-maximum power ratio for the 12 V TSS system. The testing of the large composite supercapacitor pouch cells and the 12 V TSS system proves the validity of the bottom-up approach, validates the design and the proposed electric circuit model and its parameters, fitted according to experimental data of small laboratory cells and applied successfully to the large cells, and proves the high quality of the scaled up fabrication processes. The 12 V TSS power system of seven large composite supercapacitor cells satisfies the set criteria of energy and maximum power for the specified duration, 15 Wh and 4.2 kW respectively, at a total mass of 3.94 kg, below the original set limit of 5 kg.

    Elaheh Hojaji, Eleftherios I. Andritsos, Zhuangnan Li, Manish Chhowalla, Constantina Lekakou, Qiong Cai (2022)DFT Simulation-Based Design of 1T-MoS2 Cathode Hosts for Li-S Batteries and Experimental Evaluation, In: International journal of molecular sciences23(24) Mdpi

    The main challenge in lithium sulphur (Li-S) batteries is the shuttling of lithium polysulphides (LiPSs) caused by the rapid LiPSs migration to the anode and the slow reaction kinetics in the chain of LiPSs conversion. In this study, we explore 1T-MoS2 as a cathode host for Li-S batteries by examining the affinity of 1T-MoS2 substrates (pristine 1T-MoS2, defected 1T-MoS2 with one and two S vacancies) toward LiPSs and their electrocatalytic effects. Density functional theory (DFT) simulations are used to determine the adsorption energy of LiPSs to these substrates, the Gibbs free energy profiles for the reaction chain, and the preferred pathways and activation energies for the slow reaction stage from Li2S4 to Li2S. The obtained information highlights the potential benefit of a combination of 1T-MoS2 regions, without or with one and two sulphur vacancies, for an improved Li-S battery performance. The recommendation is implemented in a Li-S battery with areas of pristine 1T-MoS2 and some proportion of one and two S vacancies, exhibiting a capacity of 1190 mAh/g at 0.1C, with 97% capacity retention after 60 cycles in a schedule of different C-rates from 0.1C to 2C and back to 0.1C.

    Kyriakos Lasetta, JOSEPH PAUL BABOO, Constantina Lekakou (2021)Modeling and simulations of the sulfur infiltration in activated carbon fabrics during composite cathode fabrication for lithium-sulfur batteries, In: Journal of composites science MDPI5(3)65 Mdpi

    During the manufacture of a composite cathode for lithium-sulfur (Li-S) batteries it is important to realize homogeneous infiltration of a specified amount of sulfur, targeted to be at least 5 mg cm(-2) to achieve good battery performance in terms of high energy density. A model of the sulfur infiltration is presented in this study, taking into account the pore size distribution of the porous cathode host, phase transitions in sulfur, and formation of different sulfur allotropes, depending on pore size, formation energy and available thermal energy. Simulations of sulfur infiltration into an activated carbon fabric at a hot-plate temperature of 175 degrees C for two hours predicted a composite cathode with 41 wt% sulfur (8.3 mg cm(-2)), in excellent agreement with the experiment. The pore size distribution of the porous carbon host proved critical for both the extent and form of retained sulfur, where pores below 0.4 nm could not accommodate any sulfur, pores between 0.4 and 0.7 nm retained S-4 and S-6 allotropes, and pores between 0.7 and 1.5 nm contained S-8.

    FOIVOS MARKOULIDIS, Adam Dawe , CONSTANTINA LEKAKOU (2020)Electrochemical double-layer capacitors with lithium-ion electrolyte and electrode coatings with PEDOT:PSS binder, In: Journal of Applied Electrochemistry

    Although typical electrochemical double-layer capacitors (EDLCs) operate with aqueous or lithium-free organic electrolytes optimized for activated carbon electrodes, there is interest in EDLCs with lithium-ion electrolyte for applications of lithium ion capacitors and hybridized battery-supercapacitor devices. We present an experimental study of symmetric EDLCs with electrolyte 1 M LiPF6 in EC:EMC 50:50 v/v and electrode coatings with 5 wt% SBR or PEDOT:PSS binder at 5 or 10 wt% concentration, where for the PEDOT:PSS containing electrodes pseudocapacitance effects were investigated in the lithium-ion electrolyte. Two different electrode coating fabrication methods were explored, doctor blade coating and spraying. It was found that EDLCs with electrodes with either binder had a stability window of 0–2 V in the lithium-ion electrolyte. EDLCs with electrodes with 10 wt% PEDOT:PSS binder yielded cyclic voltammograms with pseudocapacitance features indicating surface redox pseudocapacitance in the doctor blade coated electrodes, and intercalation and redox phenomena for the sprayed electrodes. The highest energy density in discharge was exhibited by the EDLC with doctor blade-coated electrodes and 10 wt% PEDOT:PSS binder, which combined good capacitive features with surface redox pseudocapacitance. In general, EDLCs with sprayed electrodes reached higher power density than doctor blade coated electrodes.

    A Santucci, A Sorniotti, C Lekakou (2013)Model predictive control for the power-split between supercapacitor and battery for automotive applications, In: 2013 IEEE International Electric Vehicle Conference, IEVC 2013

    Research and development of energy storage systems are almost entirely dominated by the need for continuously increasing their performance, reducing weight, cost, and increasing efficiency. The combination of battery and supercapacitor within the hybrid energy storage system (HESS) involves the management of the power between the two devices. The objective of this study is to develop a novel model predictive controller for the HESS of a through-the- road-parallel hybrid electric vehicle, which aims to extend the battery life. Results in terms of battery life expectancy and HESS energy efficiency are presented and discussed. © 2013 IEEE.

    C Lekakou, M Foderingham, MK Abbas, A Sorniotti, JP Cosmas (2014)Photovoltaic energy source, Battery-supercapacitor energy storage/power system, electric vehicle charge station, in the grid, In: WIT Transactions on Engineering Sciences88pp. 305-310

    A system of photovoltaic (PV)-supercapacitor battery is outlined in this study for the charging of a battery for a mid-power electric vehicle (EV) or hybrid vehicle, in conjunction with charging contributions from the grid. Computational models have been developed for each component of the system, namely the PV, supercapacitor, and battery. Model predictions are presented for each system component and validated with experimental data. The required PV area for the charging of the battery of a mid-range EV or hybrid vehicle has also been estimated. © 2014 WIT Press.

    S Amico, C Lekakou (2004)Flow through a two-scale porosity, oriented fibre porous medium, In: TRANSPORT IN POROUS MEDIA54(1)pp. 35-53 KLUWER ACADEMIC PUBL
    U Mohammed, C Lekakou, L Dong, MG Bader (2000)Shear deformation and micromechanics of woven fabrics, In: COMPOSITES PART A-APPLIED SCIENCE AND MANUFACTURING31(4)pp. 299-308 ELSEVIER SCI LTD
    SC Amico, C Lekakou (2002)Axial impregnation of a fiber bundle. Part 1: Capillary experiments, In: POLYMER COMPOSITES23(2)pp. 249-263 SOC PLASTICS ENG INC
    E Heardman, C Lekakou, MG Bader (2004)Flow monitoring and permeability measurement under constant and transient flow conditions, In: COMPOSITES SCIENCE AND TECHNOLOGY64(9)pp. 1239-1249 ELSEVIER SCI LTD
    EC Vermisoglou, T Giannakopoulou, GE Romanos, N Boukos, M Giannouri, C Lei, C Lekakou, C Trapalis (2015)Non-activated high surface area expanded graphite oxide for supercapacitors, In: APPLIED SURFACE SCIENCE358pp. 110-121 ELSEVIER SCIENCE BV
    L Dong, C Lekakou, MG Bader (2000)Solid-mechanics finite element simulations of the draping of fabrics: a sensitivity analysis, In: COMPOSITES PART A-APPLIED SCIENCE AND MANUFACTURING31(7)pp. 639-652 ELSEVIER SCI LTD
    E Heardman, C Lekakou, MG Bader (2001)In-plane permeability of sheared fabrics, In: COMPOSITES PART A-APPLIED SCIENCE AND MANUFACTURING32(7)pp. 933-940 ELSEVIER SCI LTD
    L Dong, C Lekakou, MG Bader (2001)Processing of composites: Simulations of the draping of fabrics with updated material behaviour law, In: JOURNAL OF COMPOSITE MATERIALS35(2)pp. 138-163 TECHNOMIC PUBL CO INC
    D Lamprou, P Zhdan, F Labeed, C Lekakou (2011)Gelatine and gelatine/elastin nanocomposites for vascular grafts: processing and characterization., In: J Biomater Appl26(2)pp. 209-226

    This study involves the preparation, microstructural, physical, mechanical, and biological characterization of novel gelatine and gelatine/elastin gels for their use in the tissue engineering of vascular grafts. Gelatine and gelatine/elastin nanocomposite gels were prepared via a sol-gel process, using soluble gelatine. Gelatine was subsequently cross-linked by leaving the gels in 1% glutaraldehyde. The cross-linking time was optimized by assessing the mass loss of the cross-linked gels in water and examining their mechanical properties in dynamic mechanical tests. Atomic force microscopy (AFM) studies revealed elastin nanodomains, homogeneously distributed and embedded in a bed of gelatine nanofibrils in the 30/70 elastin/gelatine gel. It was concluded that the manufactured nanocomposite gels resembled natural arteries in terms of microstructure and stiffness. The biological characterization involved the culture of rat smooth muscle cells (SMCs) on tubular gelatine and gelatine/ elastin nanocomposite gels, and measurements of the scaffold diameter and the cell density as a function of time.

    S Amico, C Lekakou (2001)An experimental study of the permeability and capillary pressure in resin-transfer moulding, In: COMPOSITES SCIENCE AND TECHNOLOGY61(13)pp. 1945-1959 ELSEVIER SCI LTD
    SC Amico, C Lekakou (2002)Axial impregnation of a fiber bundle. Part 2: Theoretical analysis, In: POLYMER COMPOSITES23(2)pp. 264-273 SOC PLASTICS ENG INC
    C Lei, F Markoulidis, Z Ashitaka, C Lekakou (2013)Reduction of porous carbon/Al contact resistance for an electric double-layer capacitor (EDLC), In: ELECTROCHIMICA ACTA92pp. 183-187 PERGAMON-ELSEVIER SCIENCE LTD
    C Lekakou, O Moudam, F Markoulidis, T Andrews, JF Watts, GT Reed (2011)Carbon-based fibrous EDLC capacitors and supercapacitors, In: Journal of Nanotechnology2011409382

    This paper investigates electrochemical double-layer capacitors (EDLCs) including two alternative types of carbon-based fibrous electrodes, a carbon fibre woven fabric (CWF) and a multiwall carbon nanotube (CNT) electrode, as well as hybrid CWF-CNT electrodes. Two types of separator membranes were also considered. An organic gel electrolyte PEO-LiCIO4-EC-THF was used to maintain a high working voltage. The capacitor cells were tested in cyclic voltammetry, charge-discharge, and impedance tests. The best separator was a glass fibre-fine pore filter. The carbon woven fabric electrode and the corresponding supercapacitor exhibited superior performance per unit area, whereas the multiwall carbon nanotube electrode and corresponding supercapacitor demonstrated excellent specific properties. The hybrid CWF-CNT electrodes did not show a combined improved performance due to the lack of carbon nanotube penetration into the carbon fibre fabric.

    EM Kampouris, CD Papaspyrides, CN Lekakou (1987)A model recovery process for scrap polystyrene foam by means of solvent systems, In: Conservation and Recycling10(4)pp. 315-319

    A solvent technique is studied for the recovery of polystyrene (PS) foam waste. The model process proposed ensures removal of any impurities present and comprises dissolution of the starting material, filtering, reprecipitation, thorough washing of the polymer grains obtained and drying. The solvent mixtures involved are separated by distillation for re-use. The following criteria are considered: (a) the rheological behaviour of the PS solutions prepared, (b) the yield of the process of polymer of acceptable grain size and (c) sufficient solvent/non-solvent separation. On the basis of these criteria, methyl ethyl ketone/n-hexane or methanol and p-xylene/n-heptane are suggested as effective solvent/non-solvent systems. © 1988.

    O Moudam, T Andrews, C Lekakou, JF Watts, G Reed (2013)Carbon Nanotube-Epoxy Nanocomposites: Correlation and Integration of Dynamic Impedance, Dielectric, and Mechanical Analyses, In: JOURNAL OF NANOMATERIALSARTN 80185 HINDAWI PUBLISHING CORP

    Electrospinning was used in innovative electrospinning rigs to obtain tubular and flat fibrous structures with controlled fiber orientation with the aim to be used as scaffolds for biomedical applications, more specifically in the tissue engineering of vascular and orthopedic grafts. Gelatine and hydroxyapatite (HA)-gelatine solutions of various compositions were tried and electrospinning of continuous fibers was maintained for gelatine and up to 0.30 g/g HA-gelatine solutions in 2,2,2-trifluoroethanol (TFE). Small diameter tubular scaffolds were electrospun with axial fiber orientation and flat scaffolds were cut from fiber mats electrospun around a wired drum substrate. The fibrous mats were crosslinked using a glutaraldehyde solution and subjected to image analysis of SEM micrographs, water swelling tests, and mechanical testing. Fiber diameter in the electrospun scaffolds could be varied depending on the feed solution concentration and composition whereas fiber orientation was affected by the processing conditions. After crosslinking, the 0.30 g/g HA-gelatine scaffolds absorbed the minimum amount of water after 48 h soaking and they had the highest Young's modulus, 60 MPa, and highest strength, 3.9 MPa.

    C Lei, F Markoulidis, P Wilson, C Lekakou (2015)Phenolic carbon cloth-based electric double-layer capacitors with conductive interlayers and graphene coating, In: JOURNAL OF APPLIED ELECTROCHEMISTRY46(2)pp. 251-258 SPRINGER

    Phenolic resin-derived activated carbon (AC) cloths are used as electrodes for large-scale electric double-layer capacitors or supercapacitors. To increase the energy and power density of the supercapacitor, the contact resistance between the carbon cloth and the aluminium foil current collector is reduced by modifying the Al current collectors. Different modified Al current collectors, including Toyal-Carbo®(surface-modified Al), DAG® (deflocculated Acheson™ graphite) coating and poly(3,4-ethylenedioxythiophene) (PEDOT) coating, have been tested and compared. The use of modified Al current collectors are shown to greatly reduce the contact resistance between the AC cloth and the Al foil. Another solution investigated in this study is to coat AC cloth with graphene through electrophoretic deposition (EPD). The graphene coated AC cloth is shown increased the capacitance and greatly reduced internal resistance.

    RA Saunders, C Lekakou, MG Bader (1999)Compression in the processing of polymer composites 2. Modelling of the viscoelastic compression of resin-impregnated fibre networks, In: COMPOSITES SCIENCE AND TECHNOLOGY59(10)pp. 1483-1494 ELSEVIER SCI LTD
    EC Vermisoglou, M Giannouri, N Todorova, T Giannakopoulou, C Lekakou, C Trapalis (2016)Recycling of typical supercapacitor materials., In: Waste management & research : the journal of the International Solid Wastes and Public Cleansing Association, ISWA34(4)pp. 337-344 Sage

    A simple, facile and low-cost method for recycling of supercapacitor materials is proposed. This process aims to recover some fundamental components of a used supercapacitor, namely the electrolyte salt tetraethyl ammonium tetrafluoroborate (TEABF4) dissolved in an aprotic organic solvent such as acetonitrile (ACN), the carbonaceous material (activated charcoal, carbon nanotubes) purified, the current collector (aluminium foil) and the separator (paper) for further utilization. The method includes mechanical shredding of the supercapacitor in order to reduce its size, and separation of aluminium foil and paper from the carbonaceous resources containing TEABF4by sieving. The extraction of TEABF4from the carbonaceous material was based on its solubility in water and subsequent separation through filtering and distillation. A cyclic voltammetry curve of the recycled carbonaceous material revealed supercapacitor behaviour allowing a potential reutilization. Furthermore, as BF4 (-)stemming from TEABF4can be slowly hydrolysed in an aqueous environment, thus releasing F(-)anions, which are hazardous, we went on to their gradual trapping with calcium acetate and conversion to non-hazardous CaF2.

    Richard Reece, Constantina Lekakou, Paul A. Smith, Rossana Grilli, Christos Trapalis (2019)Sulphur-linked graphitic and graphene oxide platelet-based electrodes for electrochemical double layer capacitors, In: Journal of Alloys and Compounds792pp. 582-593 Elsevier

    This study presents novel investigations of sulphur-graphitic nanoplatelet (S-GNP) and sulphur-microwave expanded graphene oxide (S-MWGO) composite electrodes for structural electrochemical double layer capacitors (EDLCs) with liquid organic electrolyte 1 M TEABF4 (tetraethylammonium tetrafluoroborate) in propylene carbonate (PC). Elucidating the chemical structure of these electrodes, XPS (X-ray photoelectron spectroscopy) and Raman spectroscopy indicated the presence of CSSC links while mixed EDX (energy dispersive X-ray spectroscopy) elemental maps displayed elemental S outlining the edges of nanoplatelets, concluding the presence of S-links between nanoplatelets. While S-linking improved the mechanical properties and ensured structural integrity of the produced monoliths without the need of any binder, it also decreased the specific surface area of the resulting materials. Furthermore, additional sulphur might have been trapped in other forms, amounting to up to 26 wt% sulphur in the composite graphitic and graphene oxide-based electrodes. Three-point bend testing yielded that an S-GNP-MWCNT monolith with 20 wt% S and 0.24 wt% MWCNT exhibited similar mechanical properties to those of a rigid polyurethane foam. The same S-GNP-MWCNT monolith exhibited an average electrode capacitance of 12.2 F g−1 during discharge at 2.2 mA/cm2. An S-MWGO-MWCNT monolith electrode with 9.6 wt% S, 16.4 wt% carbon black and 0.24 wt% MWCNT exhibited an average electrode capacitance of 64.9 F g−1 during discharge at 2.2 mA/cm2 but higher resistance than the S-GNP electrodes.

    Y Elsayed, C Lekakou, F Labeed, P Tomlins (2016)Fabrication and characterisation of biomimetic, electrospun gelatin fibre scaffolds for tunica media-equivalent, tissue engineered vascular grafts, In: MATERIALS SCIENCE & ENGINEERING C-MATERIALS FOR BIOLOGICAL APPLICATIONS61pp. 473-483 ELSEVIER SCIENCE BV

    It is increasingly recognised that biomimetic, natural polymers mimicking the extracellular matrix (ECM) have low thrombogenicity and functional motifs that regulate cell–matrix interactions, with these factors being critical for tissue engineered vascular grafts especially grafts of small diameter. Gelatin constitutes a low cost substitute of soluble collagen but gelatin scaffolds so far have shown generally low strength and suture retention strength. In this study, we have devised the fabrication of novel, electrospun, multilayer, gelatin fibre scaffolds, with controlled fibre layer orientation, and optimised gelatin crosslinking to achieve not only compliance equivalent to that of coronary artery but also for the first time strength of the wet tubular acellular scaffold (swollen with absorbed water) same as that of the tunica media of coronary artery in both circumferential and axial directions. Most importantly, for the first time for natural scaffolds and in particular gelatin, high suture retention strength was achieved in the range of 1.8–1.94 N for wet acellular scaffolds, same or better than that for fresh saphenous vein. The study presents the investigations to relate the electrospinning process parameters to the microstructural parameters of the scaffold, which are further related to the mechanical performance data of wet, crosslinked, electrospun scaffolds in both circumferential and axial tubular directions. The scaffolds exhibited excellent performance in human smooth muscle cell (SMC) proliferation, with SMCs seeded on the top surface adhering, elongating and aligning along the local fibres, migrating through the scaffold thickness and populating a transverse distance of 186 μm and 240 μm 9 days post-seeding for scaffolds of initial dry porosity of 74 and 83%, respectively.

    C Lekakou, R Fields, C Lei, F Markoulidis (2016)The Composite Supercapacitor, In: Energy Technology4(4)pp. 517-525 Wiley

    Inspired by the design of composite materials, we propose a new composite supercapacitor that comprises an integrated cell with high-power- and high-energy-related electrode materials. The composite electrochemical double-layer capacitor (EDLC) is the equivalent circuit of a high-power EDLC of power P1 and energy E1 and a high-energy EDLC of power P2 and energy E2 connected in parallel. A methodology is proposed and validated in this study for the design of an application-specific composite supercapacitor of power P and energy E with P1/E1>P/E>P2/E2. The methodology was tested successfully in medium- and large-sized application-specific composite supercapacitors, which were fabricated in the form of pouch cells using an organic electrolyte. The application-specific composite supercapacitors offered weight reductions of 40–60 % compared with supercapacitors based on the high-power- or on high-energy-related electrode materials only.

    Elizabeth Shumbayawonda, Ali A. Salifu, Constantina Lekakou, John P. Cosmas (2018)Numerical and Experimental Simulations of the Wireless Energy Transmission and Harvesting by a Camera Pill, In: Journal of Medical Devices12(2) American Society of Mechanical Engineers (ASME)

    This paper investigates the energy transmitted to and harvested by a camera pill travelling along the gastrointestinal tract. It focuses on the transmitted electromagnetic (EM) energy in the frequency range of 0.18 to 2450 MHz and compares it to the mechanical energy due to the motion of the pill and the force exerted from the intestine in its peristalsis onto the pill, and the electrochemical energy due to the change of pH along the path of the pill. A comprehensive multilayer EM power transmission model is constructed and implemented in a numerical code, including power attenuation through each layer and multi-reflections at material interfaces. Computer simulations of EM power transmission through a multilayer abdomen to a pill travelling in the intestine are presented for the human abdominal cavity as well as phantom organs and phantom environments, coupled with corresponding experimental studies using these phantom components and environments. Two types of phantom abdomen are investigated: a ballistic gel and a multilayer duck breast. Phantom small intestine involves gelatin gel layers with embedded phantom chyme. Due to limitations related to the energy safety limit of skin exposure and energy losses in the transmission through the abdomen and intestines, inductive range frequencies are recommended which may yield energy harvesting of 10-50 mWh during 8 hours of pill journey, complemented by about 10 mWh of mechanical energy and 10 mWh of electrochemical energy harvesting, in addition to about 330 mWh typically stored in the coin batteries of a camera pill.

    C Lei, N Amini, F Markoulidis, P Wilson, S Tennison, C Lekakou (2013)Activated carbon from phenolic resin with controlled mesoporosity for an electric double-layer capacitor (EDLC), In: JOURNAL OF MATERIALS CHEMISTRY A1(19)pp. 6037-6042 ROYAL SOC CHEMISTRY
    GSE Antipas, C Lekakou, P Tsakiropoulos (2011)Microstructural characterisation of Al - Hf and Al - Li - Hf spray deposits, In: Materials Characterization62(4)pp. 402-408
    X Wang, T Geng, Y Elsayed, C Saaj, C Lekakou (2015)A unified system identification approach for a class of pneumatically-driven soft actuators, In: ROBOTICS AND AUTONOMOUS SYSTEMS63pp. 136-149 ELSEVIER SCIENCE BV
    F Markoulidis, C Lei, C Lekakou (2013)Fabrication of high-performance supercapacitors based on transversely oriented carbon nanotubes, In: APPLIED PHYSICS A-MATERIALS SCIENCE & PROCESSING111(1)pp. 227-236 SPRINGER
    Richard Reece, Constantina Lekakou, Paul Smith (2018)A structural supercapacitor based on activated carbon fabric and a solid electrolyte, In: Materials Science and Technology35(3)pp. pp 368-375 Taylor & Francis

    This paper presents investigations to create a structural supercapacitor with activated carbon fabric electrodes and a solid composite electrolyte, consisting of organic liquid electrolyte 1 M TEABF4 in propylene carbonate and an epoxy matrix where different compositions were considered of 1:2, 1:1 and 2:1 w/w epoxy: liquid electrolyte. Vacuum-assisted resin transfer moulding was used for the impregnation of the electrolyte mixture into the electrochemical double layer capacitor (EDLC) assembly. The best electrochemical performance was exhibited by the 1:2 w/w epoxy: liquid electrolyte ratio, with a cell equivalent-in-series resistance of 160  cm2 and a maximum electrode specific capacitance of 101.6 mF g-1 while the flexural modulus and strength were 0.3 GPa and 29.1 MPa, respectively, indicating a solid EDLC device.

    Richard Reece, Constantina Lekakou, Paul A. Smith (2020)A High-Performance Structural Supercapacitor, In: ACS Applied Materials and Interfaces American Chemical Society

    Considering the low specific capacitance of structural solid supercapacitors, which is due to the low ion diffusivity in solid electrolytes and the small specific surface area of some structural electrodes such as carbon fiber fabrics, novel structural supercapacitor designs are proposed and evaluated in this study based on supercapacitor-functional sandwich composite materials. Typical electrochemical double layer capacitors (EDLCs) are proposed with liquid organic electrolyte 1 M TEABF4 in PC (propylene carbonate). In the innovative sandwich structured composites, supercapacitors are embedded in the skins and integrated in the honeycomb core where the aluminium faces of the core constitute the current collectors of the supercapacitor-functional core. The sandwich composite material exhibited a flexural modulus of 5.07 GPa and a flexural strength of 413.9 MPa. The EDLCs embedded in the skins increased the skin flexural modulus and strength by 47% and 56%, respectively, for embedded lateral EDLCs, and by 91% and 106%, respectively, for embedded lateral and longitudinal EDLCs. Compared to typical EDLCs with the same electrolyte, the structural supercapacitors in this study demonstrated superior specific electrode capacitance, Csp,el = 153 F g-1 for the honeycomb supercapacitor and Csp,el = 95.7 F g-1 for the skin supercapacitor, translating to overall structural composite material performance of 0.68 Wh/m2honeycomb and 30.5 W/m2honeycomb for the supercapacitor-functional honeycomb, and 0.02 Wh/m2skin and 5.4 W/m2skin for the supercapacitor-functional skin.

    C Lekakou, MAK Johari, D Norman, MG Bader (1996)Measurement techniques and effects on in-plane permeability of woven cloths in resin transfer moulding, In: COMPOSITES PART A-APPLIED SCIENCE AND MANUFACTURING27(5)pp. 401-408 ELSEVIER SCI LTD
    Y Elsayed, C Lekakou, F Labeed, P Tomlins (2016)Smooth muscle tissue engineering in crosslinked electrospun gelatin scaffolds, In: JOURNAL OF BIOMEDICAL MATERIALS RESEARCH PART A104(1)pp. 313-321 WILEY-BLACKWELL
    Seri M. Mustaza, Chakravarthini M. Saaj, Francisco J. Comin, Wissam A. Albukhanajer, Duale Mahdi, Constantina Lekakou (2018)Stiffness Control for Soft Surgical Manipulators, In: International Journal of Humanoid Robotics15(5)1850021 World Scientific Publishing

    Tunable stiffness control is critical for undertaking surgical procedures using soft manipulators. However, active stiffness control in soft continuum manipulators is very challenging and has been rarely realized for real-time surgical applications. Low stiffness at the tip is much preferred for safe navigation of the robot in restricted spaces inside the human body. On the other hand, high stiffness at the tip is demanded for efficiently operating surgical instruments. In this paper, the manipulability and characteristics of a class of soft hyper-redundant manipulator, fabricated using Ecoflex-0050TM silicone, is discussed and a new methodology is introduced to actively tune the stiffness matrix, in real-time, for disturbance rejection and stiffness control. Experimental results are used to derive a more accurate description of the characteristics of the soft manipulator, capture the varying stiffness effects of the actuated arm and consequently offer a more accurate response using closed loop feedback control in real-time. The novel results presented in this paper advances the state-of-the-art of tunable stiffness control in soft continuum manipulators for real-time applications.

    EC Vermisoglou, E Devlin, T Giannakopoulou, G Romanos, N Boukos, V Psycharis, C Lei, C Lekakou, D Petridis, C Trapalis (2014)Reduced graphene oxide/iron carbide nanocomposites for magnetic and supercapacitor applications, In: JOURNAL OF ALLOYS AND COMPOUNDS590pp. 102-109 ELSEVIER SCIENCE SA
    C Lekakou, J Cowley, CE Dickinson (1997)Injection moulding of self-reinforcing polymers and polymer blends, In: JOURNAL OF MATERIALS SCIENCE32(5)pp. 1319-1324 CHAPMAN HALL LTD
    C Lekakou, I Kontodimopoulos, AK Murugesh, YL Chen, DA Jesson, JF Watts, PA Smith (2008)Processability studies of silica-thermoset polymer matrix nanocomposites, In: POLYMER ENGINEERING AND SCIENCE48(2)pp. 216-222 JOHN WILEY & SONS INC

    The aim of this study is to investigate the processability of silica-thermoset polymer matrix nanocomposites in terms of dispersion of silica nanoparticles and their effect on curing. Two thermosetting resins were considered, an epoxy and a polyester resin, with 5 % silica, although 1% silica was also used in preliminary studies in the polyester system. Various combinations of mechanical mixing and sonication were investigated for the dispersion of silica nanoparticles under different processing conditions and times in solvent-free and solvent-containing systems. It was found that the best dispersion route involved a solvent-aided dispersion technique. Consequently, different procedures for the solvent removal were investigated. Optical microscopy and SEM were used to characterize the resulting nanocomposites. DSC and rheological DMTA tests demonstrated that the silica nanoparticles shorten the gel time and promote curing in these thermosetting systems.

    J Brandao, E Spieth, C Lekakou (1996)Extrusion of polypropylene .1. Melt rheology, In: POLYMER ENGINEERING AND SCIENCE36(1)pp. 49-55 SOC PLASTICS ENG INC
    Foivos Markoulidis, Nadia Todorova, Rossana Grilli, Constantina Lekakou, Christos Trapalis (2019)Composite Electrodes of Activated Carbon and Multiwall Carbon Nanotubes Decorated with Silver Nanoparticles for High Power Energy Storage, In: Journal of Composites Science3(4)97 MDPI

    Composite materials in electrodes for energy storage devices can combine different materials of high energy density, in terms of high specific surface area and pseudocapacitance, with materials of high power density, in terms of high electrical conductivity and features lowering the contact resistance between electrode and current collector. The present study investigates composite coatings as electrodes for supercapacitors with organic electrolyte 1.5 M TEABF4 in acetonitrile. The composite coatings contain high surface area activated carbon (AC) with only 0.15 wt% multiwall carbon nanotubes (MWCNTs) which, dispersed to their percolation limit, offer high conductivity. The focus of the investigations is on the decoration of MWCNTs with silver nanoparticles, where smaller Ag crystallites of 16.7 nm grew on carboxylic group-functionalized MWCNTs, MWCNT–COOH, against 27–32 nm Ag crystallites grown on unfunctionalized MWCNTs. All Ag-decorated MWCNTs eliminate the contact resistance between the composite electrode and the current collector that exists when undecorated MWCNTs are used in the composite electrodes. Ag-decorated MWCNT–COOH tripled the power density and Ag-decorated MWCNT additive doubled the power density and increased the maximum energy density by 6%, due to pseudocapacitance of Ag, compared to composite electrodes with undecorated MWCNTs.

    C Lekakou, J Brandao (1996)Extrusion of polypropylene .2. Process analysis of the metering zone, In: POLYMER ENGINEERING AND SCIENCE36(1)pp. 56-64 SOC PLASTICS ENG INC
    C Lekakou, MAKB Johari, MG Bader (1996)Compressibility and flow permeability of two-dimensional woven reinforcements in the processing of composites, In: POLYMER COMPOSITES17(5)pp. 666-672 SOC PLASTICS ENG INC
    RA Saunders, C Lekakou, MG Bader (1998)Compression and microstructure of fibre plain woven cloths in the processing of polymer composites, In: COMPOSITES PART A-APPLIED SCIENCE AND MANUFACTURING29(4)pp. 443-454 ELSEVIER SCI LTD
    TM Schmidt, TM Goss, SC Amico, C Lekakou (2009)Permeability of Hybrid Reinforcements and Mechanical Properties of their Composites Molded by Resin Transfer Molding, In: JOURNAL OF REINFORCED PLASTICS AND COMPOSITES28(23)pp. 2839-2850 SAGE PUBLICATIONS LTD
    C Lei, C Lekakou (2013)Activated carbon-carbon nanotube nanocomposite coatings for supercapacitor applications, In: SURFACE & COATINGS TECHNOLOGY232pp. 326-330 ELSEVIER SCIENCE SA
    A Salifu, Constantina Lekakou, Fatima Labeed (2016)Multilayer cellular stacks of gelatin-hydroxyapatite fiber scaffolds for bone tissue engineering, In: Journal of Biomedical Materials Research: Part A105(3)pp. 779-789 Wiley

    Multilayer cellular stacks of crosslinked, electrospun 25 wt% hydroxyapatite (HA)-gelatin and pure gelatin fiber scaffolds, seeded with human foetal osteoblasts (hFOBs), were studied for up to 18 days in static and dynamic cell culture. Two types of stack models were investigated: a four-layer stack with cells seeded at the bottom surface of the first/top layer and the top surface of the fourth/bottom layer, so that the two middle layers were not seeded with cells with the aim to act as continuing conduits of culture medium and nutrients supply to the adjacent cell-populated zones; a three-layer stack with cells seeded at the bottom surface of each layer. hFOBs exhibited lower migration rate through the stack thickness for the 25 wt% HA-gelatin scaffolds compared to the pure gelatin scaffolds, due to the small pores of the former. Hence, the regularly seeded three-layer stack maintained cell-free porous zones in all layers through which the culture medium could continuously perfuse, while good fusion was achieved at the interface of all layers via the cross-migrating cells with a preference to downwards vertical migration attributed to gravity. Dynamic cell culture conditions enhanced overall cell growth by about 6% for the regularly seeded three-layer stack.

    RA Saunders, C Lekakou, MG Bader (1999)Compression in the processing of polymer composites 1. A mechanical and microstructural study for different glass fabrics and resins, In: COMPOSITES SCIENCE AND TECHNOLOGY59(7)pp. 983-993 ELSEVIER SCI LTD
    Daniyar Sadykov, Lhadi Nouicer, Constantina Lekakou (2017)Hybrid Woven Glass Fibre Fabric-Multi-walled Carbon Nanotube-Epoxy Composites Under Low Rate Impact, In: Journal of Composites Science1(1) MDPI AG (Basel, Switzerland)

    This research work addresses the issue of developing light composite materials with increased ability for impact energy absorption. Novel, hybrid plain woven glass fibre fabric-epoxy laminates with multi-walled carbon nanotube (MWNT) interlayers were fabricated in this study so that (a) only a few MWNT interlayers were placed close to the face of the laminate to be subjected to impact and (b) the interlayers were fabricated via innovative wide-line electrospinning of MWNT/epoxy/solvent solutions, depositing a mixture of aligned fibres and spray on the woven glass fibre fabrics; the laminate was then fabricated via resin transfer moulding (RTM). Hybrid nano-micro-composite laminates with 0.15 wt% MWNT were prepared with this method and were subjected to single low rate impact tests. It was found that the optimised hybrid laminates had 22% greater total penetration energy translated to 15% weight reduction in the laminate armour for an equivalent amount of energy penetration.

    AA Salifu, Constantina Lekakou, Fatima Labeed (2017)Electrospun oriented gelatin-hydroxyapatite fibre scaffolds for bone tissue engineering, In: Journal of Biomedical Materials Research Part A105(7)pp. 1911-1926 Wiley

    Tissue engineering of human foetal osteoblast (hFOB) cells was investigated on gelatin-hydroxyapatite (HA), crosslinked, electrospun oriented fibre scaffolds at the different hydroxyapatite concentrations of 0, 10, 20 and 25 wt% in the dry fibres and different fibre diameter, pore size and porosity of scaffolds. Rheological tests and proton NMR spectroscopy were conducted for all solutions used for electrospinning. It was found that 25 wt% HA-gelatin scaffolds electrospun at 20 kV led to the greatest cell attachment, cell proliferation and extracellular matrix (ECM) production while fibre orientation improved the mechanical properties, where crosslinked electrospun 25 wt% HA-gelatin fibre scaffolds yielded a Young’s modulus in the range of 0.5 to 0.9 GPa and a tensile strength in the range of 4 to 10 MPa in the fibre direction for an applied voltage of 20 to 30 kV, respectively, in the electrospinning of scaffolds. Biological characterisation of cell seeded scaffolds yielded the rate of cell growth and ECM (collagen and calcium) production by the cells as a function of time; it included cell seeding efficiency tests, alamar blue cell proliferation assay, alkaline phosphate (ALP) assay, collagen assay, calcium colorimetric assay, fluorescence microscopy for live and dead cells, and scanning electron microscopy (SEM) for cell culture from 1 to 18 days. After 18 days, cells seeded and grown on the 25 wt% HA-gelatin scaffold, electrospun at 20 kV, reached production of collagen at 370 g/L and calcium production at 0.8 mM.

    CR Rios, SL Ogin, C Lekakou, KH Leong (2007)A study of damage development in a weft knitted fabric reinforced composite. Part 1: Experiments using model sandwich laminates, In: COMPOSITES PART A-APPLIED SCIENCE AND MANUFACTURING38(7)pp. 1773-1793 ELSEVIER SCI LTD
    P Wilson, C Lei, C Lekakou, JF Watts (2014)Transverse charge transport in inkjet printed poly (3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS), In: ORGANIC ELECTRONICS15(9)pp. 2043-2051 ELSEVIER SCIENCE BV

    Transverse (z) alignment of PEDOT grains was demonstrated in inkjet printed PEDOT:PSS. This explained the superior transverse charge conduction mode in inkjet printed PEDOT:PSS films, best fitted by the Efros-Shklovskii 1D-VRH (variable range hopping) model in this study compared with spin coated PEDOT:PSS films, which have demonstrated layers of generally in-plane aligned PEDOT:PSS grains. The findings of this study, regarding the microstructure of inkjet printed PEDOT:PSS films and their transverse charge transport model, justify measurements of the transverse conductivity of inkjet printed films in this study being 600 times higher than that of spin coated films. In addition, it was found that the addition of 5 wt% DMSO in the printing PEDOT:PSS ink lowers the workfunction by 3% approximately.

    I Papailias, M Giannouri, A Trapalis, N Todorova, T Giannakopoulou, N Boukos, C Lekakou (2015)Decoration of crumpled rGO sheets with Ag nanoparticles by spray pyrolysis, In: APPLIED SURFACE SCIENCE358pp. 84-90 ELSEVIER SCIENCE BV
    C Lekakou, D Lamprou, U Vidyarthi, E Karopoulou, P Zhdan (2008)Structural hierarchy of biomimetic materials for tissue engineered vascular and orthopedic grafts, In: JOURNAL OF BIOMEDICAL MATERIALS RESEARCH PART B-APPLIED BIOMATERIALS85B(2)pp. 461-468 WILEY-LISS
    AK Murugesh, A Uthayanan, C Lekakou (2010)Electrophoresis and orientation of multiple wall carbon nanotubes in polymer solution, In: APPLIED PHYSICS A-MATERIALS SCIENCE & PROCESSING100(1)pp. 135-144 SPRINGER
    EC Vermisoglou, T Giannakopoulou, G Romanos, M Giannouri, N Boukos, C Lei, C Lekakou, C Trapalis (2015)Effect of hydrothermal reaction time and alkaline conditions on the electrochemical properties of reduced graphene oxide, In: APPLIED SURFACE SCIENCE358pp. 100-109 ELSEVIER SCIENCE BV
    Seri Mastura Mustaza, Y. Elsayed, Constantina Lekakou, S. Chakravarthini, J. Fras (2019)Dynamic Modeling of Fiber-Reinforced Soft Manipulator: A Visco-hyperelastic Material-based Continuum Mechanics Approach, In: Soft Robotics6(3) Mary Ann Liebert

    Robot assisted surgery is gaining popularity worldwide and there is increasing scientific interest to explore the potential of soft continuum robots for minimally invasive surgery. However, the remote control of soft robots is much more challenging compared to their rigid counterparts. Accurate modeling of manipulator dynamics is vital to remotely control the diverse movement configurations and is particularly important for safe interaction with the operating environment. However, current dynamic models applied to soft manipulator systems are simplistic and empirical which restricts the full potential of the new soft robots technology. Therefore, this paper provides a new insight into the development of a nonlinear dynamic model for a soft continuum manipulator based on a material model. The continuum manipulator used in this study is treated as a composite material and a modified non-linear Kelvin-Voigt material model is utilized to embody the visco-hyperelastic dynamics of soft silicone. The Lagrangian approach is applied to derive the equation of motion of the manipulator. Simulation and experimental results prove that this material modeling approach sufficiently captures the nonlinear time- and rate-dependent behavior of a soft manipulator. Material model-based closed-loop trajectory control was implemented to further validate the feasibility of the derived model and increase the performance of the overall system.

    N Todorova, T Giannakopoulou, N Boukos, E Vermisoglou, Constantina Lekakou, C Trapalis (2016)Self-propagating solar light reduction of graphite oxide in water, In: Applied Surface Science.391(Part B)pp. 601-608 Elsevier

    Graphite Oxide (GtO) is commonly used as an intermediate material for preparation of graphene in the form of reduced graphene oxide (rGO). Being a semiconductor with tunable band gap rGO is often coupled with various photocatalysts to enhance their visible light activity. The behavior of such rGO-based composites could be affected after prolonged exposure to solar light. In the present work, the alteration of the GtO properties under solar light irradiation is investigated. Water dispersions of GtO manufactured by oxidation of natural graphite via Hummers method were irradiated into solar light simulator for different periods of time without addition of catalysts or reductive agent. The FT-IR analysis of the treated dispersions revealed gradual reduction of the GtO with the increase of the irradiation time. The XRD, FT-IR and XPS analyses of the obtained solid materials confirmed the transition of GtO to rGO under solar light irradiation. The reduction of the GtO was also manifested by the CV measurements that revealed stepwise increase of the specific capacitance connected with the restoration of the sp2 domains. Photothermal self-propagating reduction of graphene oxide in aqueous media under solar light irradiation is suggested as a possible mechanism. The self-photoreduction of GtO utilizing solar light provides a green, sustainable route towards preparation of reduced graphene oxide. However, the instability of the GtO and partially reduced GO under irradiation should be considered when choosing the field of its application.

    Mathew Rutt, Constantina Lekakou, Paul Smith, Alessandro Sordon, Claudio Santoni (2018)Methods for Process-related Resin Selection and Optimisation in High-Pressure Resin Transfer Moulding, In: Materials Science and Technology35(3)pp. 327-335 Taylor & Francis

    A framework for process-related resin selection and optimisation is proposed in the context of research and development for industrial applications of high-pressure resin transfer moulding (HP-RTM). The first stage involves the validation of the reaction kinetics model by differential scanning calorimetry (DSC) and determination of the reaction constants, and the characterisation of viscosity, storage- and viscous-shear moduli by dynamic mechanical analysis (DMA) in a rheometer as a function of time. It also includes capillary pressure measurements for a curing resin impregnating a vertical fibre yarn. Process-related resin selection criteria are based on the optimisation of cycle time, including filling time against gel time, micro-infiltration time and demould time. The proposed framework and the associated test and analysis methodologies have been applied to three epoxy resin systems in connection with carbon fibre reinforcement.

    Y. Elsayed, C. Lekakou, P. Tomlins (2019)Modeling, simulations and optimization of smooth muscle cell tissue engineering for the production of vascular grafts, In: Biotechnology and Bioengineering116(6)pp. pp 1509-1522 Wiley

    The paper presents a transient, continuum, two‐phase model of the tissue engineering in fibrous scaffolds, including transport equations for the flowing culture medium, nutrient and cell concentration with transverse and in‐plane diffusion and cell migration, a novel feature of local in‐plane transport across a phenomenological pore and innovative layer‐by‐layer cell filling approach. The model is successfully validated for the smooth muscle cell tissue engineering of a vascular graft using crosslinked, electrospun gelatin fiber scaffolds for both static and dynamic cell culture, the latter in a dynamic bioreactor with a rotating shaft on which the tubular scaffold is attached. Parametric studies evaluate the impact of the scaffold microstructure, cell dynamics, oxygen transport, and static or dynamic conditions on the rate and extent of cell proliferation and depth of oxygen accessibility. An optimized scaffold of 75% dry porosity is proposed that can be tissue engineered into a viable and still fully oxygenated graft of the tunica media of the coronary artery within 2 days in the dynamic bioreactor. Such scaffold also matches the mechanical properties of the tunica media of the human coronary artery and the suture retention strength of a saphenous vein, often used as a coronary artery graft.

    Jonathan Pope, Constantina (Tina) Lekakou (2019)Thermoelectric polymer composite yarns and an energy harvesting wearable textile, In: Smart Materials and Structures28(9)095006pp. 1-14 IOP Publishing

    A thermoelectric wearable is proposed based on an innovative 3d wearable design, with p- type polymer impregnated cotton yarns and n-type polymer impregnated cotton yarns, where the ratio of the p-/n-type yarn cross-sections is optimised to maximise the thermoelectric conversion efficiency. The thermoelectric yarns are embroidered through a double-layer cotton fabric, using plain-stitch, and connected via painted silver electrodag patches. The first stage of this study involved the characterisation of P3HT-, PEDOT:PSS- and PCBM-cotton fabric composite samples, in terms of their fibre volume fraction, specific heat capacity, thermal conductivity, electrical conductivity, Seebeck coefficient, Z and power factors. In this initial assessment, P3HT was selected as the p-type polymer compared to PEDOT:PSS, and PCBM was selected as the n-type polymer. A small, 3d wearable prototype was fabricated and tested: it exhibited a Seebeck coefficient of 380 mV K-1 but a relatively high resistance. It was estimated that scaling up this thermoelectric wearable to body coverage would produce about 1.5-2 mW for a temperature difference of 40 oC applied on the thermoelectric device.

    C Lekakou, A Hearn, AK Murugesh, B Le Page (2007)Liquid composite moulding of fibre nanocomposites, In: MATERIALS SCIENCE AND TECHNOLOGY23(4)pp. 487-491 MANEY PUBLISHING
    Y Elsayed, Constantina Lekakou, T Ranzani, M Cianchetti, M Morino, A Arezzo, A Menciassi, T Geng, Chakravarthini Saaj, M Chirurgia (2015)Crimped braided sleeves for soft, actuating arm in robotic abdominal surgery, In: Minimally Invasive Therapy & Allied Technologies24(4)pp. 204-210 Taylor & Francis

    Background: This paper investigates different types of crimped, braided sleeve used for a soft arm for robotic abdominal surgery, with the sleeve required to contain balloon expansion in the pneumatically actuating arm while it follows the required bending, elongation and diameter reduction of the arm. Material and methods: Three types of crimped, braided sleeves from PET (BraidPET) or nylon (BraidGreyNylon and BraidNylon, with different monofilament diameters) were fabricated and tested including geometrical and microstructural characterisation of the crimp and braid, mechanical tests and medical scratching tests for organ damage of domestic pigs. Results: BraidPET caused some organ damage, sliding under normal force of 2-5 N; this was attributed to the high roughness of the braid pattern, the higher friction coefficient of polyethylene terephthalate (PET) compared to nylon, and the high frequency of the crimp peaks for this sleeve. No organ damage was observed for the BraidNylon, attributed to both the lower roughness of the braid pattern and the low friction coefficient of nylon. BraidNylon also required the lowest tensile force during its elongation to similar maximum strain as that of BraidPET, translating to low power requirements.

    Constantina Lekakou, Y Elsayed, T Geng, Chakravarthini Saaj (2015)Skins and Sleeves for Soft Robotics: Inspiration from Nature and Architecture, In: Advanced Engineering Materials17(8)pp. 1180-1188

    © 2014 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim. This paper is on the design, fabrication, and testing of skins and sleeves for soft robotics with the focus on the mechanical features of the microstructure of these skins, drawing inspiration from nature and architecture. Biological inspirations drawn from animals are used for designing skin membranes or skin structures for soft robotic actuators, in particular pneumatic actuators that protect, guide, and contribute to the development of the actuated shape. The results presented in this paper will be a new step toward advancing the state-of-the-art of biologically inspired soft robots for minimally invasive surgery. Inspirations from architecture are of particular interest in the areas of formability of design and continuous flow. The report presents a trade-off study using various skin and sleeve technologies of innovative fiber structures and combinations of different materials in different innovative designs, surrounding a pneumatically actuated, soft robot of variable stiffness.

    This study includes a novel approach of applying an equivalent electric circuit model of two resistors and three constant phase elements (CPEs) to the galvanostatic charge-discharge of supercapacitors which provides virtual monitoring of the electrochemical processes taking place in parallel at different timescales and offers remarkable insights into the coexistence composition and cascade of such processes during the charge-discharge of cells at different current densities. This modelling method has been applied to analyse the performance of high energy density supercapacitors based on a microporous, phenolic-derived, activated carbon fabric (ACF) with different interlayers with the current collector (CC). Associated experimental studies deal with the challenge of overcoming the high contact resistance between the ACF and the current collector (CC) by employing innovative interlayers containing conductive features or structures to fill or bridge the interface gaps between the ACF fibers and the CC foil and the pores of the activated carbon (AC) fiber surface. Such interlayers involve tree-like microstructures of carbon black nanoparticles or deflocculated graphite platelets or multiwall carbon nanotubes (MWCNTs) deposited electrophoretically on the aluminium foil and the ACF. The use of PEDOT:PSS binder in such interlayer raises performance to maximum 44 Wh/kg and 9 kW/kg for electrolyte 1.5 M TEABF4/AN. These are further raised by 17% and 13%, respectively, using electrolyte 1.5 M SBPBF4/AN, and by 19% (both) using a thin polyolefinic separator against the thicker, cellulose-based separator.

    JOSEPH PAUL BABOO, Shumaila Babar, Dhaval Kale, Constantina Lekakou, Giuliano M. Laudone (2021)Designing a Graphene Coating-Based Supercapacitor with Lithium Ion Electrolyte: An Experimental and Computational Study via Multiscale Modeling, In: Nanomaterials (Basel, Switzerland)11(11) Mdpi

    Graphene electrodes are investigated for electrochemical double layer capacitors (EDLCs) with lithium ion electrolyte, the focus being the effect of the pore size distribution (PSD) of electrode with respect to the solvated and desolvated electrolyte ions. Two graphene electrode coatings are examined: a low specific surface area (SSA) xGNP-750 coating and a high SSA coating based on a-MWGO (activated microwave expanded graphene oxide). The study comprises an experimental and a computer modeling part. The experimental part includes fabrication, material characterization and electrochemical testing of an EDLC with xGNP-750 coating electrodes and electrolyte 1M LiPF6 in EC:DMC. The computational part includes simulations of the galvanostatic charge-discharge of each EDLC type, based on a continuum ion transport model taking into account the PSD of electrodes, as well as molecular modeling to determine the parameters of the solvated and desolvated electrolyte ions and their adsorption energies with each type of electrode pore surface material. Predictions, in agreement with the experimental data, yield a specific electrode capacitance of 110 F g(-1) for xGNP-750 coating electrodes in electrolyte 1M LiPF6 in EC:DMC, which is three times higher than that of the high SSA a-MWGO coating electrodes in the same lithium ion electrolyte.

    A system of photovoltaic (PV)-supercapacitor battery is outlined in this study for the charging of a battery for a mid-power electric vehicle (EV) or hybrid vehicle, in conjunction with charging contributions from the grid. Computational models have been developed for each component of the system, namely the PV, supercapacitor, and battery. Model predictions are presented for each system component and validated with experimental data. The required PV area for the charging of the battery of a mid-range EV or hybrid vehicle has also been estimated. © 2014 WIT Press.

    Ahmed Saleh, Constantina Lekakou, John J Doherty (2021)An investigation into energy harvesting and storage to power a more electric regional aircraft, In: ADVANCES IN AIRCRAFT AND SPACECRAFT SCIENCE8(1)pp. 17-30 Techno-Press

    This is an investigation for a more electric regional aircraft, considering the ATR 72 aircraft as an example and the electrification of its four double slotted flaps, which were estimated to require an energy of 540 Wh for takeoff and 1780 Wh for landing, with a maximum power requirement of 35.6 kW during landing. An analysis and evaluation of three energy harvesting systems has been carried out, which led to the recommendation of a combination of a piezoelectric and a thermoelectric harvesting system providing 65% and 17%, respectively, of the required energy for the actuators of the four flaps. The remaining energy may be provided by a solar energy harvesting photovoltaic system, which was calculated to have a maximum capacity of 12.8 kWh at maximum solar irradiance. It was estimated that a supercapacitor of 232 kg could provide the energy storage and power required for the four flaps, which proved to be 59% of the required weight of a lithium iron phosphate (LFP) battery while the supercapacitor also constitutes a safer option.

    Joshua Bates, FOIVOS MARKOULIDIS, Constantina Lekakou, Giuliano M. Laudone (2021)Design of Porous Carbons for Supercapacitor Applications for Different Organic Solvent-Electrolytes, In: C7(1)15 Mdpi

    The challenge of optimizing the pore size distribution of porous electrodes for different electrolytes is encountered in supercapacitors, lithium-ion capacitors and hybridized battery-supercapacitor devices. A volume-averaged continuum model of ion transport, taking into account the pore size distribution, is employed for the design of porous electrodes for electrochemical double-layer capacitors (EDLCs) in this study. After validation against experimental data, computer simulations investigate two types of porous electrodes, an activated carbon coating and an activated carbon fabric, and three electrolytes: 1.5 M TEABF(4) in acetonitrile (AN), 1.5 M TEABF(4) in propylene carbonate (PC), and 1 M LiPF6 in ethylene carbonate:ethyl methyl carbonate (EC:EMC) 1:1 v/v. The design exercise concluded that it is important that the porous electrode has a large specific area in terms of micropores larger than the largest desolvated ion, to achieve high specific capacity, and a good proportion of mesopores larger than the largest solvated ion to ensure fast ion transport and accessibility of the micropores.

    Constantina Lekakou, Phillip Patrick Kearney, Stephen Belcher (2022)Measurement of the Heat Transfer Properties of Carbon Fabrics via Infrared Thermal Mapping, In: Journal of composites science MDPI6(6)155 MDPI

    The aim of this paper is to determine the heat transfer properties of biaxial carbon fabrics of different architectures, including non-crimp stitch bonded fabrics, plain, twill and satin woven fabrics. The specific heat capacity was determined via DSC (differential scanning calorimetry). A novel method of numerical analysis of temperature maps from a video using a high-resolution thermal camera is investigated for the measurement of the in-plane and transverse thermal diffusivity and conductivity. The determined thermal conductivity parallel to the fibers of a non-crimp stitch bonded fabric agrees well with the theoretical value calculated employing the rule of mixtures. The presence of voids due to the yarn crossover regions in woven fabrics leads to a reduced value of transverse thermal conductivity, especially in the single ply measurements of this study.

    K Kanas, C Lekakou, N Vrellos, AM Korsunsky (2008)FEA and Experimental Studies of Adaptive Composite Materials with SMA Wires, In: CURRENT THEMES IN ENGINEERING SCIENCE 20071045pp. 101-110
    S De Pinto, Q Lu, P Camocardi, Christoforos Chatzikomis, Aldo Sorniotti, Constantina Lekakou (2016)Electric vehicle driving range extension using photovoltaic panels, In: VPPC Conference Proceedings

    This paper investigates the potential benefits of photovoltaic (PV) panels on electric vehicles. In addition to the PV panels on the roof of the car, in this study a PV panel is installed below the windshield to increase energy capture when the car is parked. An electro-mechanical actuator makes the PV panel disappear under the roof when the passengers are in the vehicle. The paper presents the simulation model of the overall PV architecture, including the DC/DC converter and the energy storage system. Based on recorded temperature and solar irradiance profiles, the model calculates the energy input and the corresponding range extension. The resulting values are discussed for a prototype four-wheel-drive urban electric vehicle operating in five European locations.

    C Lei, C Lekakou (2012)Carbon-based nanocomposite EDLC supercapacitors, In: Nanotechnology 2010: Advanced Materials, CNTs, Particles, Films and Composites1pp. 176-179
    AD Gosman, C Lekakou, S Politis, RI Issa, MK Looney (1992)Multidimensional modeling of turbulent two-phase flows in stirred vessels, In: AICHE JOURNAL38(12)pp. 1946-1956

    This article outlines a computational procedure for the prediction of dispersed two-phase, solid-liquid and gas-liquid, turbulent flows in baffled, impeller-stirred vessles common in the chemical industries. A two-flow Eulerian model is employed, based on the main assumption of interpenetrating coexisting continua. Mean momentum and mass conservation equations are solved for each phase and turbulent closure is effected by extending the single phase k- epsilon turbulence model to two-phase flows. The resulting set of highly coupled equations is solved by a two-phase implicit algorithm, PISO-2P, which allows calculation for a wide range of phase fraction, particle size and phase density ratios. Predictions are presented for solid-liquid and gas-liquid (bubbly) flows. Comparisons are made with experimental data for the mean phase velocities and volume fraction, mean slip velocity and turbulence quantities. (from Authors)

    U Vidyarthi, P Zhdan, C Gravanis, C Lekakou (2007)Gelatine-hydroxyapatite nanocomposites for orthopaedic applications, In: World Congress on Engineering 2007, Vols 1 and 2pp. 1251-1256
    CN Lekakou, SM Richardson (1986)SIMULATION OF REACTING FLOW DURING FILLING IN REACTION INJECTION MOLDING (RIM)., In: Polymer Engineering and Science26(18)pp. 1264-1275

    This paper deals with computer simulation of the filling stage of the Reaction Injection Molding (RIM) process for cavities of rectangular, cylindrical, and disc shapes. The computer model is in two parts: the main flow and the flow by the moving front. In the main flow part, the transient equations of axial momentum, energy and species conservation and also the continuity equation are solved numerically by finite-difference methods using a moving, changing mesh. In the flow front part, which is quite novel, the transient (parabolic) vorticity, energy and species conservation equations and the elliptic stream function equation are again solved by finite-difference methods. Results are presented for all three cavity shapes and those for rectangular cavities are compared with the experimental results of previous investigators.

    S Mustaza, D Mahdi, CM Saaj, W Albukhanajer, C Lekakou, Y Elsayed, J Fras (2015)Tuneable Stiffness Design of Soft Continuum Manipulator
    U Vidyarthi, P Zhdan, C Gravanis, C Lekakou (2008)Gelatine-Hydroxyapatite Nano-composites for Orthopaedic Applications, In: AM Korsunsky (eds.), CURRENT THEMES IN ENGINEERING SCIENCE 20071045pp. 81-90
    CN Lekakou, SM Richardson (1988)Computer simulation of the filling and curing stages in RIM: Sensitivity analysis on reaction kinetics, In: Plastics and Rubber Processing and Applications10(1)pp. 17-25

    This work presents results obtained using a computer model of the filling and curing stages in reaction injection moulding (RIM), the main emphasis being given to the rheology and reaction kinetics. Three types of viscosity relation and four types of reaction kinetics are included so that the computer code can be applied to a wide range of RIM materials. Comparisons of computational results with experimental ones are made for a polyurethane system. A sensitivity analysis, mainly on reaction kinetics, is performed for three types of chemical system. The variables which govern the RIM process are combined in three main dimensionless groups, namely the Reynolds, Graetz and Damkohler numbers. The effect of changes in each of these numbers on the gelling time, reaction time and maximum temperature is studied.

    U Mohammed, C Lekakou, MG Bader (1999)Experimental studies and computer simulations of the draping of woven fabrics, In: PROCEEDINGS OF THE FIFTH INTERNATIONAL CONFERENCE ON FLOW PROCESSES IN COMPOSITE MATERIALSpp. 53-60
    EM Kampouris, CD Papaspyrides, CN Lekakou (1988)MODEL PROCESS FOR THE SOLVENT RECYCLING OF POLYSTYRENE., In: Polymer Engineering and Science28(8)pp. 534-537

    A model solvent technique is presented according to which polystyrene (PS) foam scrap is recovered in the form of small grains. The process mainly comprises dissolution of the waste into benzene or toluene, filtering, dispersion of the solution into water, and subsequent distillation. The alternative solvent/non-solvent systems have been studied on the basis of solution rheology, operating conditions during the recycling procedure, and extents of recovery of PS and solvent. Eventually, the toluene/water system has been chosen for a larger scale experiment (LSE), the product of which was used for characterization work. No influence on critical properties was detected due to the solvent technique followed.

    F Markoulidis, C Lei, C Lekakou, E Figgemeier, D Duff, S Khalil, B Martorana, I Cannavaro (2012)High-performance Supercapacitor cells with Activated Carbon/MWNT nanocomposite electrodes, In: IOP Conf.Series:MaterialsScienceandEngineering 40 (2012) 01202140

    The purpose of this work was to investigate and improve the performance of supercapacitor cells with carbon-based nanocomposite electrodes. The electrode structure comprised activated carbon (AC), four types of multi-wall nanotubes (MWNTs) and two alternative polymer binders, Polyvinyl alcohol (PVA) or Polyvinylidene fluoride (PVDF). Electrode fabrication involved various stages of mixing and dispersion of the AC powder and carbon nanotubes, rolling and coating of the AC/MWNT/binder paste on an aluminium substrate which also served as current collector. The organic electrolyte utilised was 1M tetraethylammonium tetrafluoroborate (TEABF4) fully dissolved in propylene carbonate (PC). All devices were of the electrochemical double layer capacitor (EDLC) type, incorporating four layers of tissue paper as separator material. The surface topography of the so fabricated electrodes was investigated with scanning electrode microscopy (SEM). Overall cell performance was evaluated with a multi-channel potentiostat/galvanostat/impedance analyser. Each supercapacitor cell was subjected to Cyclic Voltammetry (CV) at various scan rates from 0.01 V/s to 1 V/s, Charge-Discharge at a fixed current steps (2 mA) and Electrochemical Impedance Spectroscopy (EIS) with frequency range from 10 mHz to 1 MHz. It was established that an AC-based supercapacitor with 0.15%w/w MWNT content and 30 μm roll-coated, nanocomposite electrodes provided superior energy and power and energy densities while the cells was immersed in the electrolyte; well above those generated by the AC-based EDLC cells.

    Constantina Lekakou, S Mustaza, T Crisp, Y Elsayed, Chakravarthini Saaj (2017)A Material-based Model for the Simulation and Control of Soft Robot Actuator
    U Mohammed, C Lekakou, MG Bader (2000)Experimental studies and analysis of the draping of woven fabrics, In: COMPOSITES PART A-APPLIED SCIENCE AND MANUFACTURING31(12)pp. 1409-1420
    P Wilson, C Lekakou, J Watts (2012)Electrical, Morphological and Electronic Properties of Inkjet Printed PEDOT:PSS, In: 2012 12TH IEEE CONFERENCE ON NANOTECHNOLOGY (IEEE-NANO)
    R Duncan, V Stolojan, C Lekakou (2007)Manufacture of carbon multi-walled nanotubes by the arc discharge technique, In: World Congress on Engineering 2007, Vols 1 and 2pp. 1391-1395
    S Mustaza, D Mahdi, Chakravarthini Saaj, F Comin, Constantina Lekakou (2017)Development of Tunable Stiffness Control for Soft Continuum Surgical Manipulators, In: International Journal of Humanoid Robotics World Scientific Publishing
    EC Vermisoglou, T Giannakopoulou, M Giannouri, N Boukos, C Lekakou, C Trapalis (2014)Single-step hydrothermal synthesis of reduced graphene oxide (rGO) and Fe2O3/rGO composites for supercapacitor applications, In: 16th European Conference on Composite Materials, ECCM 2014

    Reduced graphene oxide sheets were prepared by hydrothermal method. IR and XRD data revealed that both reduction and exfoliation occur during hydrothermal process of graphite oxide (GtO) aqueous dispersions. The concentration of GtO dispersion, process duration and alkali conditions e.g. presence of K2CO3 influence quality characteristics of the produced materials as it was emerged by Raman spectroscopy. Hydrothermal process allows in parallel with reduction and exfoliation the intercalation with nanoparticles (NPs). By using FeCl3.6H2O in presence of NaAc as a precursor, a composite of reduced graphene oxide (rGO) intercalated with iron oxide NPs (Fe2O3/rGO) was synthesized. Electrochemical measurements indicated that the sample treated with K2CO3 had the best performance in terms of capacitance. Both rGO and Fe2O3/rGO are materials of particular interest for supercapacitor applications.

    C Lekakou, MG Bader (1998)Mathematical modelling of macro- and micro-infiltration in resin transfer moulding (RTM), In: COMPOSITES PART A-APPLIED SCIENCE AND MANUFACTURING29(1-2)pp. 29-37
    Josh Bates, CONSTANTINA LEKAKOU, QIONG CAI, FOIVOS MARKOULIDIS, Robert Prof Slade, Gareth Hinds (2019)Modelling and Simulations of Energy Storage Devices

    In electrochemistry, numerical models are used to predict the activity of energy storage devices such as batteries and supercapacitors. Novel battery technologies, such as lithium-sulphur batteries, benefit from simulation studies in optimising their materials, and more specifically in this study, their porous cathodes. Porous carbon is typically used as the electrode in different supercapacitor configurations, as well as the cathode structural material in Li-S batteries. Previous models in the literature simulate the porous electrodes with a single uniform pore size. In this project a novel model has been devised, incorporating multiple pore sizes of the electrode material, determined from a pore size distribution.

    There is an increasing interest to advance the state-of-the-art of soft robots due to its capability to extend the limits of traditional rigid robot manipulators. Many novel soft robots have been designed and proposed in the recent years of which, inflatable soft robots attract considerable research efforts, as the actuation mechanism is read- ily compatible with bio-inspired designs. However, the research on inflatable soft robots is currently at an early stage. Most prototypes lack a proper mathematical model and control design for real-time application. This study proposes a unified model identification framework for the pneumatic bending soft actuator and similar flexible systems. This method is one of the first attempts to deal with the complex nonlinear dynamics of soft robots that is challenging to model. The outcomes of this research could improve the current modelling and control design of inflatable soft robots for more advanced medical applications. Firstly, a statistics-based model identification approach is investigated. It introduces a newly developed model identification model structure, namely the Difference In- put Outputs PieceWise Linear Orthonormal Basis Function (DIO-PWL-OBF). This method collects local dynamic responses and linearises local subsystems that are approximated by a set of optimally selected OBFs. With the DIO setting, the switching between different subsystems is smooth especially in the input direction-dependent situations. The advantage is that this method can capture the local dynamics accurately and the local models can be used to construct global dynamics without adding offset terms or nonlinear weighting terms. The identification approach by the DIO-PWL-OBF model structure has been experimentally validated for common bending profiles using a three-chambered soft pneumatic actuator made of silicone. Regarding an identified DIO-PWL-OBF model structure, a solution that further improves its local partition and local linear approximations is presented. The anal- ysis shows that, under the DIO setting, the switching between two subsystems is coupling invariant whether in the same input direction or not. Utilising this unique feature, an iterative refinement algorithm is developed. The algorithm consists of two main steps, adjusting the offsets on individuals DIO sequences and redoing the linear approximate under eigenvalue constraints. The refinement algorithm has been experimentally validated by the soft actuator in a typical bending case.

    CONSTANTINA LEKAKOU, JOSEPH PAUL BABOO, FOIVOS MARKOULIDIS, Robert Prof Slade (2019)Increasing Energy Density and Power Density in Hybridised Supercapacitor-Battery Devices

    Research is presented aiming to increase both power and energy density of lithium batteries by applying composite cathodes containing sulphur, which has a high theoretical specific capacity of 1675 Ah/kgS and is an abundant and low-cost material, and increase the power density of the cells by creating battery-supercapacitor hybrids with the hybridisation carried out at electrode material level. The focus of current research worldwide has been to increase the cyclability of lithium-sulphur (Li-S) batteries, which has been accomplished by devising composite sulphur cathodes, to avoid cathode degradation due to the expansion of sulphur to accommodate the formation of sulphides, and various functionalisation approaches to trap the sulphides and avoid the 'shuttle' effect during charge. However, the theoretical capacity of sulphur has not been achieved even at first discharge, lowering the expected energy density, and this is further compounded by the fact that only a fraction of the composite cathode is sulphur. Modelling studies have shown that access of all sulphur by the Li+ ions in the micropores is critical and formation of sufficient amounts of higher order sulphides during the first stage of discharge is needed, to be able to obtain a long second stage discharge plateau. The first stage of our study is focused on demonstrating homogeneous and deep sulphur impregnation of porous carbonaceous material to create cathodes with more than 50 wt% sulphur in a supercapacitor-type, porous, host matrix. Repeated discharges are carried out after which we have achieved the theoretical specific capacity of sulphur at first discharge (cumulative curve in Figure 1). We shall continue with parametric studies to investigate the effect of different amounts of sulphur in the composite cathode on the pore size distribution and discharge capacity. The second part of this study includes the investigations into lithium battery-supercapacitor cells hybridised at electrode material level, in combinations of parallel and in series material parts in equivalent circuit models. The effect of the supercapacitor porous carbonaceous electrode materials on the voltage of the cell in galvanostatic charge-discharge curves will be presented in experimental investigations for half-cells of both sides and full cells. Some novel cell architectures will be presented aiming at minimising any detrimental reactions in the supercapacitor materials within the battery cell window.

    C Lekakou, C Lei, F Markoulidis, A Sorniotti (2012)Nanomaterials and Nanocomposites for High Energy/High Power Supercapacitors, In: 2012 12TH IEEE CONFERENCE ON NANOTECHNOLOGY (IEEE-NANO)
    Y Elsayed, A Vincensi, C Lekakou, T Geng, CM Saaj, T Ranazani, M Cianchetti, A Menciassi (2014)Finite element analysis (FEA) and design optimisation of a pneumatically actuating silicone module for robotic surgery applications, In: Soft Robotics1(4)pp. 255-262 Mary Ann Liebert

    The design of a pneumatically actuated silicone module, resembling soft tissue, with three pneumatic chambers is considered and optimized in this study with the aim of using it in a soft robot arm for robotic surgery applications. Three types of silicone materials, Ecoflex 0030 and 0050 and Dragonskin 0030, have been investigated, and a constitutive model has been derived for each of them. Design optimization of the silicone module was based on finite element analysis (FEA) that was validated against experimental data of one-degree bending under one-channel actuation. This was followed by FEA parametric studies for module design optimization to minimize the ballooning effect in one-degree bending as well as reduce the actuation pressure. Modules made from Ecoflex 0030 and Ecoflex 0050 exhibited the same bending shape in FEA, but about three times higher actuation pressure was required for the harder Ecoflex 0050. Design parameters under investigation in the parametric FEA studies included the shape of the pneumatic channel cross section, the ratio of channel length to module length, the distance of channel from the module wall, and the ratio of channel to module cross-sectional area. After FEA design optimization yielded least ballooning for pneumatic chambers of semicircular cross section, an internal dragonskin structure was added internally below the module surface to enable and guide the bending under one-channel pneumatic actuation and further contain the ballooning effect: the benefits of this design were successfully verified under both FEA and experimental analysis.

    G Rebord, N Hansrisuk, B Lindsay, C Lekakou, GT Reed, JF Watts (2008)Electrofunctional Polymer Nanocomposites, In: ESTC 2008: 2ND ELECTRONICS SYSTEM-INTEGRATION TECHNOLOGY CONFERENCE, VOLS 1 AND 2, PROCEEDINGSpp. 1401-1405
    C Lekakou, S Cook, Y Deng, TW Ang, GT Reed (2006)Optical fibre sensor for monitoring flow and resin curing in composites manufacturing, In: COMPOSITES PART A-APPLIED SCIENCE AND MANUFACTURING37(6)pp. 934-938
    C Lekakou, P Wilson, D Craggs, YC Chau, AA Salifu, YL Chen, JF Watts (2009)Electrospinning of polymer nanocomposites, In: Proceedings of 17th International Conference on Composite Materials
    K Kanas, C Lekakou, N Vrellos (2007)FEA and experimental studies of adaptive composite materials with SMA wires, In: World Congress on Engineering 2007, Vols 1 and 2pp. 1329-1334
    SC Amico, C Lekakou (1999)Predictions and measurement of the permeability and capillary pressure in capillary flows through woven fabrics, In: PROCEEDINGS OF THE FIFTH INTERNATIONAL CONFERENCE ON FLOW PROCESSES IN COMPOSITE MATERIALSpp. 311-318
    E Heardman, C Lekakou, MG Bader (1999)Measurement of the principal components of the in-plane permeability of woven fabrics, In: PROCEEDINGS OF THE FIFTH INTERNATIONAL CONFERENCE ON FLOW PROCESSES IN COMPOSITE MATERIALSpp. 153-159
    C Lekakou, F Markoulidis, C Lei, A Sorniotti, J Perry, C Hoy, B Martorana, I Cannavaro, M Gosso (2012)Meso-nano and micro-nano ion transport in porous carbon composite electrodes for energy storage applications, In: ECCM 2012 - Composites at Venice, Proceedings of the 15th European Conference on Composite Materials

    In energy storage devices carbonaceous composite electrodes are a popular choice, consisting of activated carbon (ac), conductive additives and a polymeric binder matrix. The active electrode components are in the form of ac particles, ac fibres, or ac monolith combined with conductive additives such as carbon black. Activated carbon plays the most important role for storing a large amount of energy in the form of ions contained in the carbon nanopores. This study considers a modelling approach to the meso-nano and micro-nano infiltration of ions into the porous carbon structure during the operation of the energy storage device. Depending on the pore size, ion size and solvent molecule size, ions may be solvated or unsolvated as they move, where ions are solvated in meso-pores for most cases. Molecular model simulations have been performed to determine the values of the geometrical parameters of different ions, solvated and unsolvated in various solvents. A meso-nano and micro-nano ion infiltration model has been developed in this study under both steady state and dynamic conditions.

    C Lekakou, S Edwards, G Bell, SC Amico (2006)Computer modelling for the prediction of the in-plane permeability of non-crimp stitch bonded fabrics, In: COMPOSITES PART A-APPLIED SCIENCE AND MANUFACTURING37(6)pp. 820-825
    E Vermisoglou, N Todorova, G Pilatos, G Romanos, V Likodimos, N Boukos, C Lei, F Markoulidis, C Lekakou, C Trapalis (2012)Few layer graphenes decorated with silver nanoparticles, In: ECCM 2012 - Composites at Venice, Proceedings of the 15th European Conference on Composite Materials

    Graphite oxide (GO) powder was irradiated in a microwave oven and lightweight expanded graphite oxide (EGO) powder with high BET surface area 1316 m2/g was obtained. Activation of EGO was performed by impregnation in KOH solution and high temperature treatment under Ar flow, followed by annealing in vacuum (t-EGO). KOH acted more as a reducing agent diminishing the defects than as a surface modifier for high porosity. EGO and t-EGO were further decorated with Ag nanoparticles (∼40 nm) applying solar light irradiation. Along with Ag deposition the structural defects of the graphene were reduced upon photo-irradiation. It was established that among the bare graphenes the EGO exhibited the highest capacitance. From the Ag-containing composites, the KOH activated EGO acted as a supercapacitor, while the non-activated EGO as a resistant.

    C Lekakou, S Cook, TW Ang, GT Reed (2003)Optical fibre flow-sensor for composites manufacturing, In: Advanced Composites Letters12(5)pp. 211-215

    An optical fibre has been used as an intensity-based sensor for the monitoring of the fluid front infiltrating a reinforcing fibre mat in composites manufacturing. The sensor length comprised the fibre core, initially surrounded by air or vacuum and subsequently covered by the infiltrating fluid. Two configurations were tested where a step-change or a continual output signal was obtained, respectively. In the latter case, the sensor used in this study demonstrates an improvement of up to two orders of magnitude over conventional monitoring techniques used for this application. This performance is coupled with more obvious advantages of low cost, compatibility with composite fabrication, and ease of use.

    CR Rios, SL Ogin, C Lekakou, KH Leong (2004)Study of the mechanisms of fracture and mechanical properties of an engineering knitted fabric reinforced composite, In: Annual Technical Conference - ANTEC, Conference Proceedings2pp. 1384-1389

    In this work the tensile properties and failure mechanisms for a knitted fabric reinforced composite has been investigated. Two commercial composites manufactured with Milano 2×68 tex knitted fabric as a reinforcement and Derakane vinyl ester resin as matrix were analysed. The quasi-static behaviour of the materials has been analysed as a function of tested direction, including an investigation of the damage accumulation. Characterization of these materials under tensile loading has been carried out for monotonic and cyclic loading and the results have been compared with those found earlier for a single layer and the sandwich model material with epoxy resin as matrix1. Various failure mechanisms such as cracking at loop cross-over points, resin matrix cracking, fibre bundle debonding and tensile fracture of fibre bundles in failed specimens were observed.

    S Amico, C Lekakou (2000)Mathematical modelling of capillary micro-flow through woven fabrics, In: COMPOSITES PART A-APPLIED SCIENCE AND MANUFACTURING31(12)pp. 1331-1344
    CR Rios, SL Ogin, C Lekakou, KH Leong (2003)Study of progressive damage in a knitted fabric reinforced composite, In: Annual Technical Conference - ANTEC, Conference Proceedings2pp. 2188-2192

    Model sandwich laminates were manufactured by orienting the knitted cloth at a range of angles to the loading direction using a single Milano weft knitted layer sandwiched between outer plies of unidirectional glass reinforced epoxy resin in order to be able to observe progressive damage accumulation along the sample. By this way, the relationship between fibre architecture and damage accumulation under tensile loading, as well as the sequence of damage accumulation has been investigated. Damage has been found to initiate at the loop cross-over points of the knitted fabric structure for all orientations, although the further development of the damage depends on the orientation of the fabric to the applied load. The resultant transparent laminates provide a novel method of monitoring the damage development in a knitted-fabric composite as a function of increasing strain by allowing direct observation of the sequence of damage.

    R Reece, C Lekakou, PA Smith (2014)Sulphur cross-linked graphene nano platelets as structural composite supercapacitor electrodes, In: 16th European Conference on Composite Materials, ECCM 2014

    Graphene nano platelets cross-linked with elemental sulphur have been used as supercapacitor electrode material to provide successful energy storage in a structural device. Chemical crosslinking of the composite produces a mechanically stable material, with both high conductivity and surface area. Characterisation was conducted using scanning electron microscopy and energy dispersive X-ray spectroscopy. Different concentrations of graphene-sulphur are investigated, along with addition of conductive carbon black and multiwall carbon nanotubes. The effects of these variables on the performance of the sulphur cross-linked graphene as a supercapacitor electrode are presented through impedance spectrometry, cyclic voltammetry and galvanostatic charge-discharge. Analysis of the structural performance of the material is conducted by flexural three-point-bend testing.

    AA Salifu, C Lekakou (2012)Electrospinning of hydroxyapatite-gelatine scaffolds: Physical characterisation and process optimisation, In: ECCM 2012 - Composites at Venice, Proceedings of the 15th European Conference on Composite Materials

    Electrospun scaffolds of hydroxyapatite-gelatine nanocomposites were fabricated, crosslinked and subjected to image analysis, water swelling and mechanical testing. Fibre diameter and pore size of scaffolds increased with the applied voltage and the hydroxyapatite (HA) content. The scaffolds were stable in water for up to three weeks and there was a positive correlation between their mechanical properties and the applied voltage and the HA content. Maximum Young's modulus and tensile strength of 925 MPa and 9.75 MPa, respectively, were recorded for 25% HA scaffold.

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