Polymer surface chemistry: Surface mixtures, supported polyelectrolyte multilayers and heterogeneous chemical modification

Abstract

This dissertation is divided into three parts that summarize three discrete projects that are related only in their overall objective of using chemistry to rationally control polymer surface structure and properties. Each part involves polymer surface modification, but the three employ very different techniques to effect surface-chemical changes. The first part (Chapter 1) involves the preparation of surfaces containing controllable mixtures of two functionalities (alcohol/ester or hydrocarbon ester/fluorocarbon ester) from alcohol-functionalized poly(chlorotrifluoroethylene) (PCTFE-OH) and the studies of their wetting behavior as a function of composition and structure. Contact angle analyses indicate that sequential and competitive esterifications yield mixed surfaces consisting of the two functional groups distributed randomly, while compositionally similar, patchy mixed surfaces can be prepared by partial hydrolysis/re-esterification under some specific conditions. Greater contact angle hysteresis was observed on the patchy surfaces. The second part (Chapter 2) describes the layer-by-layer deposition of cationic (polyallylamine hydrochloride (PAH)) and anionic (polysodium styrenesulfonate (PSS)) polyelectrolytes onto the PCTFE-OH substrate. XPS and contact angle data indicate that the assembled layers are stratified even though the individual layers are extremely thin (0.3-4.1 A). This thickness depends both on the charge density of the first layer of PAH (controlled using pH) and the ionic strength of the PSS adsorption solution. The stoichiometry of the assembly process also varies with the ionic strength of the PSS adsorption solution. The third part (Chapter 3) involves the heterogeneous (gas-solid) chemical modification of poly(trifluoroethylene) (PF\sb3E). Chlorination of PF\sb3E is a surface-selective reaction and the extent of chlorination can be controlled by time and light intensity. The fluorination of PF\sb3E carried out using 5% F\sb2/N\sb2 yields products that exhibit similar surface properties to poly(tetrafluoroethylene) (PTFE). Very thin coatings of PF\sb3E on inorganic supports (Si wafers) were prepared by the adsorptions from THF:toluene solutions. The higher the toluene composition, the more polymer adsorbs and the rougher the substrate becomes. The amount of PF\sb3E adsorption is increased significantly by introducing a polar functional group to the polymer by maleation