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Controlled detachment of colloidal particles from fluid interfaces

Research Area: Chemistry, colloid and interface science, materials science, soft matter and nanotechnology

Supervisor: Dr Catherine Whitby

Description: Solid particles of colloidal dimensions (nanometres to micrometres) are present in many emulsions and foam formulation. The presence of particles is often desirable as they enhance stability, for example, tiny fat crystals naturally present in ice cream foams hinder coarsening of the foam by attaching to the air bubbles and forming protective shells around them. In other cases, however, the enhanced stabilization of these systems by particle attachment to drops or bubbles has undesirable outcomes. For example, highly stable emulsions can form when sea-water and crude oil are mixed, due to clays and asphaltenes collecting at the oil-water interface, causing severe environmental problems for the petroleum industry. The aim of this project is to investigate destabilization in emulsions containing particles.

Approach: Detachment of particles from drops will be studied in concentrated emulsions and in dilute emulsions consisting of two colloid laden drops being brought into close contact. The emulsions will be prepared from oil and water. Other liquids of interest include ionic liquids and immiscible polymer blends. The particles will be mineral oxides, clays, polymer lattices and metal nanoparticles. The following questions will be addressed:

• Routes for destabilization of emulsions can involve the addition of salt, polymers or surfactants, or the application of high shear, electric or magnetic fields or temperature gradients. What roles do chemical stresses (addition of salt and so on) and physical stresses play in destabilizing the emulsions containing particles?
• The mechanisms by which emulsions typically destabilize involve separation of the oil from the water due to density differences, aggregation of drops into large clusters and coarsening of drops. What is the contribution of each of those mechanisms to the way in which emulsions containing particles destabilize?
• What factors affect the time taken for an emulsion to destabilize? Can the rate at which particles detach from drops be controlled, so that, for example, emulsion destabilization can be triggered to occur quickly or over a sustained period?

References
1. J. Ralston, D. Fornasiero and R. Hayes, 'Bubble-Particle Attachment and Detachment in Flotation', International Journal of Mineral Processing, 56 (issues 1-4), 133-164 (1999).
2. R. Aveyard, B. P. Binks and J. H. Clint, 'Emulsions Stabilized Solely by Colloidal Particles', Advances in Colloid and Interface Science, 100-102, 503-546 (2003).
3. S. Arditty, C. P. Whitby, B. P. Binks, V. Schmitt and F. Leal-Calderon, 'Some General Features of Limited Coalescence in Solid-Stabilised Emulsions', European Physical Journal E, 11 (issue 3), 273-281 (2003).

Funding: International students should apply for an International Postgraduate Research Scholarship (IPRS) and a UniSA President's Scholarship (UPS). To be eligible for UPS, applicants must have a supervisor willing to nominate them for consideration.

Australian students should apply for an Australian Postgraduate Award (APA) and a UniSA Australian Postgraduate Research Award (USAPRA). 

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