Self-diffusion anisotropy of small penetrants in compressed elastomers

The anisotropy of self-diffusion of toluene in uniaxially compressed natural rubber samples with different cross-link densities was detected using the pulsed-gradient stimulated spin-echo NMR method. The effective diffusion coefficients and the displacement probabilities of toluene were measured along and perpendicular to the direction of the compression force. The diffusion anisotropy increases with increasing compression and cross-link density. The anisotropy of diffusion can be used for NMR investigations of the deformation of the polymer networks by the changes in the shape of the free volume.