Ionic coupling to plasma polymer surfaces

Abstract

The work in this thesis was aimed at the preparation of low energy surfaces via the surface attachment of fluorinated surfactant molecules. Such surface functionalisation routes are highly dependent on the chemical nature of the substrate surface. For this reason the choice of substrate materials is both all important and extremely limited. To make the process of more general appeal a method for pre-treating the substrate, using cold plasma polymerisation reactions, followed by surfactant coupling to the plasma polymer has been devised. Using this approach, the surfactant coupling process is now dependent on the surface chemistry of deposited plasma polymers and independent of substrate characteristics. In order to form highly functionalised surfaces, likely to undergo further reactions, the plasma polymerisation of acrylic acid, ally! amine and allyl alcohol was investigated. Highly functionalised acid, amine and alcohol surfaces, as shown by X-ray Photoelectron Spectroscopy (XPS) and Infrared Spectroscopy (IR), were produced by optimisation of pulsed plasma conditions. Measurement of deposition rates during plasma polymerisation reactions indicated that polymerisation can occur during the off-time of the pulsed plasma period, most likely via free radical polymerisation pathways. Highly functionalised plasma polymer surfaces thus formed were shown to couple to fluorinated surfactant molecules. The mechanism of surfactant attachment has been suggested to be ionic attraction between opposite charges on the surfactant molecule and the plasma polymer in aqueous solution. The surfaces formed give rise to oleophobic/hydrophilic behaviour. This is in marked contrast to the usual liquid repellent attributes of conventional polyelectrolyte- fluorosurfactant complexes formed by solution phase synthesis.