Microstructure of Ion-Selective Plasticized PVC Membranes Studied by Small-Angle 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 neutron scattering. In the dry membrane, inhomogeneities were found. The membrane structure is well described by a polydisperse hard-sphere model. The mean diameter of the dispersed spherical inhomogeneities is ∼6 nm, which is smaller than the estimated dimension of a single statistically curled PVC polymer chain in the membrane. The values of the best-fit parameters and their change with membrane composition suggest that the particles consist of unplasticized PVC, probably in the crystalline state. The type of plasticizer, the plasticizer content, and the addition of a lipophilic salt were found to influence the water uptake significantly. Water uptake did not change the microstructure due to the original (i.e., dry state) inhomogeneities in the membranes.