Diffusion in elastomers

Abstract

Membrane methods have been outlined for determining diffusion and solubility coefficients in systems where Fick's law is valid, and of determining the concentration dependence of D where the generalised diffusion equation (ie186-01) has to be used. Some results of measurements of D for simple molecules in elastomers lead to the view that diffusion occurs by a place change mechanism involving a zone of activation and a considerable entropy and energy of activation. The Arrhenius equation D = D0 eE/RT often gives a good description of the effect of temperature on D. A functional relationship of the form Log D0 = const.+K E/T where K is a constant has been discussed and interpreted. Systematic increases in the cross-linking of rubber caused characteristic changes in the values of D, D0, and E, and in the molecular sieve action of rubber. Solubilities and heats of solution in the series CH4, C2H6, C2H4, C3H8, n-C4H10 showed on the other hand no marked change over a range of values for the combined sulphur between 1·7 and 11·3%.