Jj. Singh, MICROSTRUCTURAL CHARACTERIZATION OF THIN POLYMER-FILMS USING THE LANGLEY LOW-ENERGY POSITRON FLUX GENERATOR, Nuclear instruments & methods in physics research. Section B, Beam interactions with materials and atoms, 79(1-4), 1993, pp. 349-352
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.