- Title
- Electrostatic polymeric liquid marbles
- Creator
- Thomas, Casey Amber
- Relation
- University of Newcastle Research Higher Degree Thesis
- Resource Type
- thesis
- Date
- 2022
- Description
- Research Doctorate - Doctor of Philosophy (PhD)
- Description
- Liquid marbles are non-wetting particles encapsulating a liquid droplet, which are traditionally formed by rolling a droplet of the liquid over the top of a bed of powder. Delivery vessels, micro-reactors and transportation vessels are some of the applications of liquid marbles, whereby the marble has an interaction with external stimuli and thus the combination of particle and liquid are chosen according to their application requirement. The current method for liquid marble formation results in difficulty with reproducibility and control during scale-up, and this lends to involving an electrostatic field to form liquid marbles instead. This method involves the delivery of particles to a pendent droplet which is above a particle bed, as the particles are charged due to the presence of an electric field. The realistic implementation of this method requires the in-depth understanding of the process, specifically the material properties and their interactions in the electric field. Further, observing the particles on the interface is critical to analysing the stabilisation of the final liquid marbles and the ultimate control of the entire process. During this thesis, the physical properties of both the particles and the liquid have been examined, increasing the understanding pertaining to the implementation of this electrostatic method into liquid marble formation. Shifting the literature toward quantitative analysis of the suitability of various particle and liquid materials, from the more qualitative previous work has allowed the elucidation of individual parameters and their importance in the process. The utilisation of polymer particles (polystyrene) throughout this thesis has facilitated simple modification of the particle properties, on a well-controlled size, shape and dispersity sample. Initially, a polypyrrole shell was added to the core polystyrene particles, allowing the modification of particle conductivity. Whilst conductivity was found to increase the distance from which particles could be transported from the bed, this alteration also modified the cohesion and hydrophobicity of the material. Herein it was found that increasing conductivity, increases ease of liquid marble formation and increasing cohesion works to negate this transportation advantage. Hydrophobicity of the particles specifically relates to the final stability of the liquid droplet, and not the initial formation step. xxv Importantly, the liquid phase was also studied to observe the impact of the conductivity, viscosity and surface tension of the droplet on the formation method. Overall, it was observed that the conductivity of the liquid made little impact, as the ions already present in tap water were sufficient to transport the charge to initiate particle transport, when compared to saline solutions. Further, the viscosity of the liquid, increased by the addition of glycerol, did not impact the extraction and transport of the particle from the bed but altered the time that the particle took to settle on the interface, and thus differing the final stability of the marble. Surface tension was found to be the most problematic liquid property, as with the addition of ethanol, decreasing the surface tension significantly resulted in the detachment of the liquid droplet far prior to the initial extraction of particles from the bed, thus hindering liquid marble formation. With this information, tap water was consistently utilised throughout experimental work, but the focus moved to understanding the charge transfer throughout the process. A statistical model was developed from the experimental data collected from charge readings throughout the circuit. This was in an attempt to understand the impact of the liquid and particle conductivities. A validation to experimental data was achieved, thus allowing the model to be refined in the future to work toward a predictive model which could be used for narrowing particle options prior to experimental work. Further work with the conductive polypyrrole coated polystyrene particles was undertaken with varying core particle sizes to understand the impact of particle size on the process. It was observed that there was a threshold size (80 µm), under which the particles suffered from a very dense packed bed regime, resisting the force of the electric field to be extracted from the bed due to high cohesive forces. Above this size, the particles were seen to easily leave the bed and be transported to the droplet interface. Interestingly, the stability of the resultant liquid marble increased with decreasing particle size, due to the same packing effect but now at the liquid interface. Thus, particles around the 80 µm exhibited a good compromise between the two competing factors. Density of the particles was another parameter studied, with the polystyrene cores being swapped for glass particles on the order of 80 µm. Increasing the density of the xxvi particles dramatically decreased the distance from which they could be extracted from the bed below the droplet. Modelling was also undertaken to understand the forces interacting with the particles, in addition to the force due to gravity. Finally, the introduction of nickel and gold shells to the polystyrene particles further elucidated the three-way interplay between cohesion, conductivity and density of the particle. Overall, increasing the cohesion and density of the material hindered the extractability and thus liquid marble formation, whilst increasing the conductivity of the particle moved to overcome these other two factors and promoted extraction and transport to the droplet. On the whole, this research has provided systematic and controlled experimental data and understanding surrounding the physical properties of both the particle and liquid involved in liquid marble formation, and whether they are cooperative or competitive in nature. For successful liquid marble formation using electrostatics, the liquid should be sufficiently conductive and exhibit high surface tension. The particles should have low cohesion and low density to reduce extractability issues, and high conductivity to ensure a high level of controllability in the process. Whilst this is the perfect scenario, no materials exhibit these parameters and thus the interplay between them all must be considered and understood to form liquid marbles electrostatically. Although this balance is required, this thesis has provided good insight into the material requirements and thus the electrostatic method is highly promising in terms of scale-up for mass liquid marble production.
- Subject
- electrostatic; polymeric; liquid marbles; particles; thesis by publication
- Identifier
- http://hdl.handle.net/1959.13/1483510
- Identifier
- uon:51120
- Rights
- Copyright 2022 Casey Amber Thomas
- Language
- eng
- Full Text
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| Thumbnail | File | Description | Size | Format | |||
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| View Details Download | ATTACHMENT01 | Thesis | 7 MB | Adobe Acrobat PDF | View Details Download | ||
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