Diffusion in Entangled and Surface Modified Polymer Systems

Ion beam analysis techniques were used to measure the concentration vs. depth profiles of deuterium labelled polymer molecules in unlabeled and/or chemically dissimilar polymer melts, for several polymer systems. In the first polymer system, the tracer diffusion coefficient of deuterated polystyrene (d-PS) molecules was measured in polystyrene (PS) matrices which were blends of high molecular weight (volume fraction phi) and low molecular weight PS. The dependence of the d-PS diffusion coefficient on phi was quantitatively predicted by the models of reptation and constraint release. In the second polymer system, diffusion of polystyrenes was studied with ring shaped chains substituted (instead of linear ones) in the tracer and/or matrix roles. The diffusion of linear tracers into ring matrices was nearly identical to linear tracer diffusion in linear matrices, a result not predicted by any current theories. Dry etching of polystyrene by four different ion and plasma methods crosslinked the exposed surface monolayer, immobilizing it and reducing its permeability to diffusion by unetched tracer molecules. The integrated thickness of the immobile layer is decreased for an increased ratio of chain scission to crosslinking. The ratio is smallest for reactive ion beam etching, intermediate for reactive ion etching, and largest for the pure plasma techniques. Diffusion was investigated in systems of the polymer polyimide (PI), produced by the imidization of polyamic acid at a temperature T_{rm i }. The effects of thermal processing (imidization) of the polymer and exposure to solvents were studied. The diffusion of deuterated polyamic acid in PI was reduced to negligible levels for T_{rm i}'s at or above 200^circ C; purely thermally activated diffusion (in the absence of solvents) was not seen for any combination of annealing temperatures up to 400^circ C. Ion beam analysis methods were developed to measure the kinetics and depth dependence of the imidization reaction in a model polyimide precursor (polyamic ethyl ester).