Microstructure of ion selective plasticized PVC membranes studied by smallangle neutron scattering

The microstructure of plasticized PVC membranes in the dry state and during the process of soaking in heavy water has been studied by small-angle neut ron scattering. In the dry membrane, inhomogeneities were found. The membra ne structure is well described by a polydisperse hard-sphere model. The mea n diameter of the dispersed spherical inhomogeneities is similar to 6 nm, w hich is smaller than the estimated dimension of a single statistically curl ed PVC polymer chain in the membrane. The values of the best-fit parameters and their change with membrane composition suggest that the particles cons ist of unplasticized PVC, probably in the crystalline state. The type of pl asticizer, the plasticizer content, and the addition of a lipophilic salt w ere found to influence the water uptake significantly. Water uptake did not change the microstructure due to the original (i.e., dry state) inhomogene ities in the membranes.