Polymer surface modification: Chemical surface modification, layer-by-layer adsorption, and surface reconstruction

The three projects, chemical modification (Chapter 1), layer-by-layer deposition (Chapter 2), and surface reconstruction (Chapter 3), that constitute this Ph.D. thesis are closely related in their overall objectives: using polymer surface modification to manipulate microscopic surface structures and control macroscopic properties. Alcohol functionality can be introduced to the surface of poly(ethylene terephthalate) (PET) using either reduction or glycolysis; both of which cleave the PET chain. Both of these modified surfaces (PET-OH$\rm\sp{R}$ and PET-OH$\rm\sp{G})$ and hydrolyzed PET (PET-OH/COOH) can be prepared using conditions that optimize surface functional group concentration, but minimize sample degradation. The surface alcohol density is higher on PET-OH$\rm\sp{G}$ than on PET-OH$\rm\sp{R}$ by a factor of $\sim$2. The concentration of alcohols on reduced surfaces is increased by solvent annealing of the PET film prior to reduction. Reactivities of PET-OH$\rm\sp{R}$ and PET-OH$\rm\sp{G}$ samples were assessed and compared. Layer-by-layer deposition of polyelectrolytes (poly(allylamine hydrochloride)) and poly(sodium styrenesulfonate)) has been used to build up multilayer films on three organic polymer substrates: PET, PET-CO$\sb2\sp-$ and PET-NH$\sb3\sp+.$ XPS and contact angle data indicate that the layers are stratified and the wettability of the multilayer assemblies is largely controlled by the identity of the outermost polyelectrolyte layer. The layer thickness and the stoichiometry of the deposition process (ammonium ion:sulfonate ion ratio) are affected by the substrate surface chemistry and can be controlled by adjusting the ionic strength of the polyelectrolyte solutions. Peel tests indicate that the multilayer assemblies show good mechanical integrity. A perfluorohexylated-C$\sb{60}$ (fullerene) was prepared and its surface activity and mobility were studied as a function of bulk concentration, annealing temperature, and annealing time in a polymer matrix (polystyrene). Perfluorohexylated-C$\sb{60}$ is extremely surface-active in the polystyrene matrix and occupies 95%-85% of the outermost 10 A-40 A (XPS results), and renders a surface that is similar to a monolayer containing -CF$\sb3$ groups (hexadecane contact angle data). Surface reconstruction studies were carried out via either spin-casting or transferring a free standing polystyrene film over the composite materials (the surface-active agent and polystyrene). Both approaches show similar behavior of migration of perfluorohexylated-C$\sb{60}$ from the bulk to the surface