Surface Modification of PDMS Films through the Addition of Amphiphiles & Oils

Abstract

There is a great deal of industrial interest in surfactant/polymer systems. In the case of fouling-release coatings, there is a desire to better understand the surface modification of coatings through the restructuring or migration of amphiphilic additives. This thesis is focussed on characterisation of model coatings consisting of a poly(dimethylsiloxane) network and one of a variety of nonionic surfactants to improve understanding of the factors affecting their accumulation at polymer interfaces, and the properties they impart on the coating. This is with the intention to feed into predictive models, capable of shifting industrial formulation away from current “brute force” methods.

Concentration profiling techniques did not reveal an excess of surfactant at the air-PDMS surface. However, adsorbed surfactant was detected at the water-PDMS interface, demonstrating a seemingly reversible accumulation of surfactant. Such accumulation yielded hydrophilised PDMS surfaces, driven by a reduction in the interfacial energy.

The phase behaviour also plays a role in the surface modification behaviour. Using members of the polyethylene glycol monododecyl ether (CE) surfactant series, a positive correlation between the measured hydrophilisation profile and the incompatibility in PDMS was found. However, such rapid hydrophilisation behaviour was not observed for the incompatible commercial fluorosurfactant Fluorolink E10-H, showing that the chemistry of the hydrophobic moiety is vital in dictating the surface behaviour. This difference between the fluorosurfactant and the oxyethylene alkyl ethers in PDMS may be due to the disintegration of surfactant self-assemblies in the latter systems. The importance of phase behaviour was further suggested by PDMS doped with tetraethylene glycol monododecyl ether (CE) being affected by the inclusion of alkane oils to the system, whereas Fluorolink E10-H-doped films showed no such behaviour.

This work has shown that it is possible to mimic many aspects of of the complex behaviour of surface-active materials in silicone resin, using simple, well-defined surfactants.