VISUALIZATION OF SOLVENT DIFFUSION IN POLYMERS BY NMR MICROSCOPY WITHRADIOFREQUENCY FIELD GRADIENTS

NMR microscopy by radio-frequency field gradients is especially well s uited for studying solvent penetration in polymers, due to the weak se nsitivity of the method to magnetic susceptibility variations caused b y object heterogeneities and to its ability to accommodate short trans verse relaxation times better than the conventional imaging procedure by static field gradients. It is shown in this paper that distinct fea tures of the swelling process can be easily observed by this method fr om two-dimensional NMR images and from the diffusion profiles provided by cross-sections through that image. A specific application of the m ethod concerns the stretched PVC for which solvent diffusion and swell ing are strongly anisotropic.