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Richard James Wood


Postgraduate Research Student
BSc Physics Class I (Hons)
+44 (0)1483 684601
34 BC 02

Academic and research departments

Department of Chemical and Process Engineering.

Research

Research interests

My publications

Publications

Wood R, Lee J, Bussemaker M (2017) A parametric review of sonochemistry: control and augmentation of sonochemical activity in aqueous solutions, Ultrasonics Sonochemistry 38 pp. 351-370 Elsevier
In this review the phenomenon of ultrasonic cavitation and associated sonochemistry is presented through system parameters. Primary parameters are defined and considered, namely; pressure amplitude, frequency and reactor design; including transducer type, signal type, vessel-transducer ratio, liquid flow, liquid height, liquid temperature and the presence of a reflective plate. Secondary parameters are similarly characterised and involve the use of gas and liquid additives to influence the chemical and physical environments. Each of the parameters are considered in terms of their effect on bubble characteristics and subsequent impact on sonochemical activity. Evidence suggests that via parametric variation, the reaction products and efficiency may be controlled. This is hypothesised to occur through manipulation of the structural stability of the bubble.
Gonzalez V., Wood R., Lee J., Taylor S., Bussemaker M. J. (2018) Ultrasound-Enhanced Hair Dye Application for Natural Dyeing Formulations, Ultrasonics Sonochemistry Elsevier
Advances made in recent years have allowed the application of colorants obtained from natural sources into textile dyeing. The use of ultrasound in the dyeing method is reported to increase dye uptake and decrease dyeing times. The aim of this work is to further extend the knowledge of natural hair dyes considering the use of ultrasound in the dyeing method with commercially available herbal dyes and using goat hair as a model for human hair. Optimal ultrasonic parameters were selected by considering the effects of sonication times (5, 10 and 15 min), frequencies (44, 400 and 1000 kHz) and total dyeing times (30, 60 and 120 min) in the morphology of the dyed hair and the colour intensity. Damage to the hair surface was evaluated by scanning electron microscopy (SEM) images, differences in colour of the dyed hair was obtained by ImageJ analysis and quantification of dye uptake was determined by UV-visible spectroscopy. The evidence from this study suggests an increase in goat hair coloration with the use of ultrasonic energy. Optimal dyeing conditions in consideration of colouration efficacy without hair damage were identified as sonication at 400 kHz for 10 min with a total dyeing time of 60 min.
Wood Richard James, Lee Judy, Bussemaker Madeleine J. (2019) Disparities between sonoluminescence, sonochemiluminescence and dosimetry with frequency variation under flow, Ultrasonics Sonochemistry Elsevier
The effects of ultrasound (frequency and pressure amplitude) and external parameters (fluid flow rate and surface stabilisation) on active sonoluminescence (SL) and sonochemical (SC) bubbles were investigated using common characterisation techniques. The SL from water, sonochemiluminescence (SCL) from luminol solutions and iodide dosimetry were studied at flow rates of 0, 24, 228 and 626 mL / min at 44, 300 and 1000 kHz with and without surface stabilisation. An increase in flow, in general, decreased SL, SCL and dosimetry caused by a reduction in collapse intensity. However, all flow rates were also able to increase SL intensity and the highest flow rate (626 mL / min) could also increase SCL and dosimetry. For SL, augmentation with flow was attributed to a reduction in coalescence bubbles which cause growth to inactive size (44 kHz) and enhancement of the standing wave at the surface of solution (300 and 1000 kHz). Where agitation at the solution surface (44 kHz) caused aeration (without stabilisation), flow may have circulated additional cavitation nuclei, increasing SL. Increases in SCL intensity and dosimetry yields were attributed to increased bubble fragmentation which was more influential for the latter process. Disparities between SCL and dosimetry are discussed in terms of gas concentration and reaction energy requirements influenced by the transient nature of the bubbles. SL and SCL had complimentary behaviour when they were located in the same regions i.e. a reduction in SL resulted in an increase in SCL as bubbles moved from stable to transient in nature. The same was not observed when SL and SCL bubbles were located in different regions. The active region for SL / SCL could differ or overlap, depending on the standing to travelling wave proportions at each frequency effecting active regions. In some cases, increased standing wave proportions throughout the reactor (with surface stabilisation) did not facilitate an increase in SL intensity, as was expected. Here, the travelling wave without stabilisation enabled a stronger area of activity toward the surface with a localised standing wave.
Wood Richard James, Lee Judy, Bussemaker Madeleine J. (2019) Combined effects of flow, surface stabilisation and salt concentration in aqueous solution to control and enhance sonoluminescence, Ultrasonics - Sonochemistry Elsevier
Sonoluminescence (SL) intensity can be increased with potassium iodide (KI) concentration, attributed to a reduction in the gas concentration of solution. However, bubble properties and active bubble distributions at different frequencies and powers also influence SL intensities. Hence, to elucidate how salt concentration affects SL intensity, a systematic study with parametric variation was undertaken. SL from KI solutions of 0.1, 1 and 2 M concentration, without flow and in the presence of flow at 24, 228 and 626 mL / min was investigated at 44, 300 and 1000 kHz. At all frequencies an increase in KI concentration caused a change in the active SL distributions. For 44 kHz, localised and standing wave field SL activity could be expanded. Flow at this frequency augmented SL and SL was maximised at the lowest power setting under stabilisation at the highest KI concentration. At 300 and 1000 kHz, attenuation of the sound field was reduced, allowing expansion of activity throughout solution. In this instance, augmentation of SL intensity was only observed under flow conditions at concentrations of 1 M (300 kHz) and 2 M (1000 kHz) under stabilisation. It was theorised that a combination of smaller bubbles at higher KI concentrations and flow effects could reduce bubble clustering and enhance field formations. This was most prevalent where the standing wave was reinforced under stabilised (44 and 300 kHz) or flow (1000 kHz) conditions, here the number of active bubbles in high pressure regions likely increases. Lastly, it was found that in KI solutions flow could localise SL activity beneath and at the flow inlet via reflection and aeration mechanisms.

In general, bubble surface instabilities (herein known as bubble transience), increase sonochemical (SC) processes and decrease processes, such as sonoluminescence (SL), that require higher collapse intensities. However, there is a limited understanding of how SL and SC processes are impacted by bubble transience in a practical sense. Thus, research and experimentation was based on the variation of parameters that would affect transience which, in turn, would determine ultrasound process outcomes.

Firstly, the ultrasonic system was characterised using SL, and the SC processes of sonochemiluminescence (SCL) and potassium iodide (KI) dosimetry. Frequencies of 20 kHz (ultrasonic horn) and 44, 300 and 1000 kHz (ultrasonic plates) were used with applied flow rates of 0, 24, 228 and 626 mL / min. These frequency and flow settings were used throughout the work unless otherwise specified. The SCL and dosimetry showed disparities throughout, attributed to changes in the energy of collapse, fragmentation and oxygen concentration / solvated electrons. At low frequency, SCL and dosimetry increased under more transient collapse conditions, as measured by the minimisation of the more pyrolytic process of SL. Here, it was theorised that bubble fragmentation and radical transfer to solution, favoured dosimetry over SCL. Further, where SL and SCL activity overlapped they showed the expected reciprocal relationship of decrease / increase with bubble transience, but where activity differed there was poor correlation.

Then, the impact of bubble transience on the intensity of collapse on SL from KI solutions (0.1, 1 and 2 M) under fluid flow and stabilised conditions were studied. At 20 kHz (horn) and 44 kHz (plate), flow reduced bubble coalescence and clustering, increasing SL intensity. However, for the 44 kHz system, at higher flow rates, bubble transience could also reduce SL. With an increase in KI concentration, at low frequency (44 kHz), localised activity could be expanded, then at higher frequencies (300 and 1000 kHz), SL activity increased towards the transducer. This indicated reduced attenuation of the sound field, attributed to a reduction in bubble size / clustering with the salt. An increase in standing wave formations (plate) or activity at the horn tip, with power (20 kHz), stabilisation (44 and 300 kHz) or flow (1000 kHz), allowed flow and salt concentration to reduce bubble coalescence / clustering in those regions. This effect could negate a decrease in SL, with increase in KI concentration at low frequency, as previously observed by other authors.

To understand how bubble transience affected SC and SL processes, the degradation of phenol and SL from phenol under fluid flow (and stabilised) conditions was investigated. Flow could augment phenol degradation at all frequencies. For the 20 kHz (horn) and 300 kHz systems, phenol degradation correlated with iodide dosimetry which suggested an oxidative process, however, 44 and 1000 kHz showed poor correlation. At 44 kHz, degradation was hypothesised to occur inside the bubbles under transient (flow) bubble conditions, as indicated by SL quenching when degradation was maximised. This was theorised to occur via nanodroplet / rectified diffusion mechanisms. At 1000 kHz the disparity between phenol degradation and iodide dosimetry was attributed to a reduction in collapse intensity and fragmentation which affected the reaction schemes. Here, the fragmentation conditions with flow were not sufficient to increase the dosimetry, whereas for degradation, fragmentation was less influential. SL analysis for higher concentrations of phenol (horn and plate transducers) showed that intensity could be increased with flow / stabilisation. This was attributed a reduction in coalescence / clustering by both flow and the surface properties of the phenol.

The methods of SC and SL characterisation were then applied to further understand the ultrasonic degradation of