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Amphiphilic block copolymers at the solid/liquid interface

Research Area: Physics, chemistry, surface engineering

Degree: Honours

Supervisors: A/Prof Rossen Sedev and Dr Jamie Schulz (ANSTO) 

Description: PEO-PPO-PEO triblock copolymers of ethylene oxide (EO) and propylene oxide (PO) are commercially available (Pluronics, Synperonics, Poloxamers) and used in various applications since their molecular weight and EO/PO ratio can be tailored to meet specific requirements. In water, these copolymers behave as surfactants: the central PPO block is hydrophobic and anchors the molecule at a hydrophobic interface while the hydrophilic PEO side blocks protrude into aqueous solution. Water is a selective solvent and these "polymeric surfactants" form micelles in the bulk solution. 

The adsorption of such copolymers at the solid/liquid interface is relevant to the wetting and spreading of liquids on hydrophobic surfaces. Hydrophobic surfaces, when treated with PEO-PPO-PEO copolymers, are subsequently wetted by alkanes and oils. Triblock copolymers are good steric stabilisers and can be used to suspend small particles or emulsion droplets in aqueous solution. When adsorbed at the solid surface, PEO-PPO-PEO copolymers are very effective in reducing protein adsorption. The hydrophobicity of the copolymers is temperature dependent, a behaviour that is of considerable interest in controlling protein adsorption in biomedical applications. 

The aim of this project is to examine the adsorption of PEO-PPO-PEO amphiphilic triblock copolymers on various polymer surfaces. The adsorbed layer will be characterised mainly by neutron reflectivity and contact angle measurements with additional insights obtained by complementary surface analysis techniques. 

The influence of molecular size, molecular asymmetry and solution composition will be systematically investigated. Specific polymers will be deposited as thin films on smooth silicon wafers and used as model adsorbing surfaces with different surface energies. The research will focus on the relation between surface energetics and block copolymer adsorption. 

Neutron reflectivity experiments may be carried out at ANSTO (Lucas Heights) and therefore the successful applicant might spend time there. The project could lead on to doctoral studies.

References 
1. Fleer, GJ, Cohen-Stuart, MA, Scheutjens, JMHM, Cosgrove, T and Vincent, B. Polymers at Interfaces. Chapman & Hall, London, 1993.
2. Alexandridis, P and Hatton, TA. Colloids Surf. A 1995, 96, 1.
3. Lu, JR, Thomas, RK and Penfold, J. Adv. Colloid Interface Sci. 2000, 84, 143.
4. Sedev, R, Steitz, R and Findenegg, GH. Physica B 2002, 315, 267. 

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