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Advanced coating of heterogeneous surfaces with complex fluids

Research Area: Chemistry, chemical engineering, colloid and interface science, physics, surface engineering

Degree: Honours

Supervisors: Laureate Prof John Ralston and A/Prof Rossen Sedev   

Description: Significance of the Proposed Research: Wetting plays a decisive role in the success or failure of many industrial and natural activities. Photographic film production, pigment dispersion, mineral flotation, the movement of water in soils, printing, optical filters, fibre cleaning [eg hair] cell membrane function and aspects of gene therapy are all controlled in large measure by wetting and dewetting processes. The liquid phase involved is most commonly, but not exclusively, water. 

Approach: The intention here is to examine the wetting of model heterogeneous surfaces, with known and controlled physical and chemical roughness. The surfaces will be in the form of rods and fibres, embracing many natural and industrial configurations. The surfaces can be patterned chemically at the micron scale and above by photomasking and stamping techniques and at the sub-micron level by self-assembly processes. 

The solid surfaces of interest will include quartz, glass and silicon wafers. The patterns can be varied considerably and individual "regions" can be tailored as desired. Physical roughening can be controlled by the introduction of grooves, pits, etc. The intention is to: 

• examine the static wetting behaviour of these tailored surfaces in the presence of complex fluids. Do components of the fluid show a preference for a given region? What is the nature of the microscopic contact angle here? Can we induce the specific interaction between a component of the complex fluid and a given surface region, for example by the interaction of an emulsified oil droplet with a hydrophobic surface site, or by the interaction with an aqueous droplet with a hydrophilic site? From a colloidal dispersion of small particles, could we encourage the small particles to selectively adsorb on some sites and not others? 
• use dynamic wetting techniques (Wilhelmy technique) and a moving rod/fibre to study how dynamic wetting occurs on these tailored surfaces in the presence of complex fluids. Particular emphasis will be placed on the molecular kinetic and hydrodynamic aspects of wetting and how they might be modified to account for the dynamic behaviour of complex fluids on tailored solid surfaces. This is critically important in coating and cleaning processes. 

This project has a major connection to Australian industry as well as to European research laboratories. It could lead on to doctoral studies.

References
1. JG Petrov, J Ralston and RA Hayes, 'Dewetting Dynamics on Heterogeneous Surfaces. A Molecular-Kinetic Treatment', Langmuir, 15, No 9, 3365-3373 (1999).
2. M Schneemilch, RA Hayes, JG Petrov and J Ralston, 'The Dynamic Wetting of a Low Energy Surface by Pure Liquids', Langmuir, 14, No 24, 7047-7051 (1998).
3. S Abbott, J Ralston, GD Reynolds and RA Hayes, 'Reversible Wettability of Photoresponsive Pyrimidine Coated Surfaces', Langmuir, 15, No. 26, 8923-8928, (1999).
4. V Peykov, A Quinn and J Ralston, 'Electrowetting: A Model for Contact Angle Saturation', Colloid and Polymer Science, 278, 789-793 (2000).
5. N Richards, A Quinn, J Ralston, G Reynolds and R Sedev, 'Light and Electric Potential Induced Reversible Wetting on Structured Surfaces', Functional Fillers and Nanoscale Materials, Edited by J Kellar, M. Herpfer and B. Moudgil, SME, 41-57, 2003. 

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