Correlation between positron annihilation and gas diffusion properties of various rubbery polymers

Abstract

Diffusion coefficients D for CO2 and CH4, their activation energies, ED, and lifetime and intensity of ortho-positronium (o-Ps), τ3 and I3 respectively, were measured for nine polymers at temperatures T from glass transition temperature Tg up to Tg+70 K. For semicrystalline polymers, D and I3 are corrected to give those in 100% amorphous samples, Da and I3, a, respectively. Average size of free volume holes probed by o-Ps, vh, Ps, is evaluated from τ3 using an empirical equation. According to the free volume model of diffusion, correlations between log(Da/T) and fractional free volume f and between ED/RT and Tf−2(df/dT) are tested, using WLF fractional free volume fWLF, vh, PsI3, and vh, Ps for f. The correlations are better for vh, Ps than for vh, PsI3. There is no correlation for fWLF. The volume fraction of free volume holes larger than the effective size of the penetrants, VF, dif, are evaluated by a proposed model from vh, Ps and volume fraction of “free space,” VF, estimated by the method of van Kreveran and Bondi. The correlations are better for VF, dif than for VF and also for vh, Ps. The apparent good correlations for vh, Ps are ascribed to the correlation of it with VF, dif. © 1993, The Society of Polymer Science, Japan. All rights reserved.