- Title
- Establishing design criteria for electrostatic liquid marble & aggregate formation
- Creator
- Lobel, Benjamin Tzui
- Relation
- University of Newcastle Research Higher Degree Thesis
- Resource Type
- thesis
- Date
- 2022
- Description
- Research Doctorate - Doctor of Philosophy (PhD)
- Description
- Liquid marbles are liquid droplets encapsulated by a non-wetting powder. They are traditionally formed by rolling the liquid drop on the powder bed. The choice of particle and liquid phase are intrinsically linked to the potential application of these marbles, some of which include micro-reaction vessels, contaminant detection and as vehicles for active ingredient delivery to target locations via interactions with a variety of external fields and forces. One of the shortcomings of liquid marbles is that it is difficult to mass-produce them in a controlled manner. A potential solution to this problem is using the electrostatic method of liquid marble and aggregate formation. This method relies on delivering particles to a pendent droplet from a particle bed using an electrostatic field. In order to optimise and implement this method an understanding of the critical forces at each stage of the process is required. Specifically, the understanding of interparticle forces within the particle bed, as well as interactions between the electric field and particles of varying conductivity and size. Finally, the behaviour of the particles on the interface is critical to successful stabilisation and control of this process. Throughout this thesis, advances in the understanding of each stage of this process and the physicochemical properties of prospective particles have been achieved. Furthermore, a paradigm shift in the approach to understanding this process has been accomplished. Previous work was primarily qualitative whilst work presented here attempts quantification of each of the forces and elucidation of their mechanism to optimise the process overall. Highly conductive copper particles of varying size were used to investigate the impact of particle conductivity and size. This demonstrated that increasing particle conductivity allowed for increased charge to be obtained by particles during dynamic particle extraction. A wider size distribution was also found to inhibit particle extraction. Large polyethylene terephthalate platelets were surface modified to become hydrophobic and conductive. Their behaviour during electrostatic extraction demonstrated that shape plays a significant role in the transport process. In this case increasing size resulted in diminished extractability due to increased surface area of interparticle contact within the bed. This was determined by calculating the extracting force on each particle and comparing to the particle weight, demonstrating the insignificance of weight as a resistive force to extraction. Finally, the sharp edges of the particles produced unusual interactions, with the electric field becoming focussed on the edges and particles being delivered edge first to the droplet. Their ability to rearrange on the interface was explained as a function of the platelet contact angle. Systematic study of the behaviour of dielectric particles was undertaken, these particles formed unusual, ordered arrays on the droplet surface. These arrays were determined to be due to the electric-field induced polarisation of the particles. Furthermore, it was demonstrated that this polarisation could take place even if there was a conductive shell on the particle, provided sufficient coating imperfections were present. Wettability appeared to have no impact on this polarisation as long as the particles remained at the interface. A model was presented using simple dipole-dipole interactions to estimate interparticle spacing in a variety of particle materials and electric field strengths. Finally, the surface free energy of surface modified glass particles was measured directly using atomic force microscopy and sessile drop measurements. Experiments in the electrostatic rig demonstrated that an increase in surface free energy inhibits particle extraction and transfer and that planar sessile drop measurements do not truly reflect the interaction in the particle bed. This study was the first attempt at direct measurement of cohesion within the particle bed with previous attempts being via deduction or modelling. Overall, this research has provided valuable insight into the physicochemical properties that either promote or diminish successful electrostatic extraction of particles to a pendent droplet to form liquid marbles. The role of particle size and size distribution in successful extraction is clearly demonstrated. Furthermore, the role of specific contact area as it relates to particle shape, size and weight is explained. Finally material properties such as surface free energy and conductivity are interrogated. In order for successful extraction a particle should exhibit a low specific contact area and surface free energy and high conductivity. Few materials exhibit this exact combination of properties so a balance must be struck in each of these domains to finely tune the extraction and encapsulation process. Despite this delicate balance the electrostatic method of liquid marble formation demonstrates great promise in developing a scalable liquid marble production process.
- Subject
- design; electrostatic; liquid marble; partilce; thesis by publication
- Identifier
- http://hdl.handle.net/1959.13/1483505
- Identifier
- uon:51121
- Rights
- Copyright 2022 Benjamin Tzui Lobel
- Language
- eng
- Full Text
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| Thumbnail | File | Description | Size | Format | |||
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| View Details Download | ATTACHMENT01 | Thesis | 10 MB | Adobe Acrobat PDF | View Details Download | ||
| View Details Download | ATTACHMENT02 | Abstract | 1012 KB | Adobe Acrobat PDF | View Details Download |