MICROSTRUCTURAL CHARACTERIZATION OF THIN POLYMER-FILMS USING THE LANGLEY LOW-ENERGY POSITRON FLUX GENERATOR

Thin, high-performance polymer films are finding widespread applicatio ns in industry, medicine, and aerospace research. Since the microstruc ture of the films determines how well they meet their theoretical prom ise, it is necessary to develop efficient techniques for producing rea sonable fluxes of low energy positrons needed for investigating thin p olymer films. We have developed a highly efficient scheme for generati ng high fluxes of slow positrons. These positrons have been successful ly used to measure lifetimes in the thin test films. The lifetime data have been used to develop two structure-property models for the lest films. The first model relates the free volume cell size (V(f)) with t he molecular weight of the polymer repeat unit (M) by an expression of the form V(f) = AM(B), where A and B are structural constants. The se cond model relates the free volume fraction (f) with the dielectric co nstant of the polymer film (epsilon) by an expression of the form 1/ep silon = (1 - f )/epsilon(R) + f/epsilon(vac) where epsilon(R) is the d ielectric constant of the microvoid-free film.