CORRELATION BETWEEN POSITRON-ANNIHILATION AND GAS-DIFFUSION PROPERTIES OF VARIOUS RUBBERY POLYMERS

Diffusion coefficients D for CO2 and CH4, their activation energies, E(D), and lifetime and intensity of ortho-positronium (o-Ps), tau3 and I3 respectively, were measured for nine polymers at temperatures T from glass transition temperature T(g) up to T(g) + 70 K. For semicrystalline polymers, D and I3 are corrected to give those in 100% amorphous samples, D(a) and I3,a, respectively. Average size of free volume holes probed by o-Ps, upsilon(h,Ps), is evaluated from tau3 using an empirical equation. According to the free volume model of diffusion, correlations between log(D(a)/T) and fractional free volume f and between E(D)/RT and Tf-2(df/dt) are tested, using WLF fractional free volume f(WLF), upsilon(h,Ps)I3, and upsilon(h,Ps) for f. The correlations are better for upsilon(h,Ps) than for upsilon(h,Ps)I3. There is no correlation for f(WLF). The volume fraction of free volume holes larger than the effective size of the penetrants, V(F,dif), are evaluated by a proposed model from upsilon(h,Ps) and volume fraction of 'free space,' V(F), estimated by the method of van Kreveran and Bondi. The correlations are better for V(F,dif) than for V(F) and also for upsilon(h,Ps). The apparent good correlations for upsilon(h,Ps) are ascribed to the correlation of it with V(F,dif).