Characterization of polydimethylsiloxane pervaporation membranes using small-angle neutron scattering

We report characterization of polydimethylsiloxane (PDMS) pervaporation membranes prepared from various conditions using the small-angle neutron scattering (SANS). The PDMS membranes were prepared by cross-linking reactions between hydroxyl terminated polydimethylsiloxane (HPDMS) and polymethylhydrosiloxane with pendant hydride (PHMS). The radius of gyration (Rg) of HPDMS and PHMS polymer chains determined from the SANS data analysis is found to be similar with the size of about 12 Å. Upon the initial cross-linking reaction at 25 °C, the Rg of the polymer was increased to 31 Å. The final membrane structure obtained after the completion of reaction is comprised of interacted polymer chains of the Rg values in the 55–61 Å range. With increasing the reaction temperature to 40 °C, about a two-fold increase in the chain length of polymer and polymer chain clustering was observed in the membrane structure. Such membrane exhibited high separation factor (α), of about 100–140 for hydrophobic organics over water. Similar high separation factor was observed for the membrane obtained by curing at 150 °C, which also has longer polymer chain and a larger polymer chain clusters. Thin film membranes coated over a porous support have loose membrane structures and show poor organic selectivity.