DIFFUSION OF LOW-MOLECULAR-WEIGHT SUBSTANCES IN GLASSY-POLYMERS DESCRIBED ON THE BASIS OF EXTENDED NONEQUILIBRIUM THERMODYNAMICS

Diffusion transfer of low-molecular-weight substances in polymer glass es, accompanied by various deviations of the process from Fick's diffu sion kinetics, is described by methods of extended nonequilibrium ther modynamics. Variables determining the non-equilibrium state include th e diffusion flux and the tensor of viscous stresses. A mathematical mo del taking into account both the cross effects between diffusion and v iscoelastic stresses and the relaxation of the system to local equilib rium is formulated and analyzed. For the comparable temporal and spati al scales of the mass transfer and nonlocality in the system, this mod el leads to a concentration profile with a wave front propagating at a constant velocity. This pattern is characteristic, for example, of a diffusion kinetics in the so-called Case II.