Bipolar membrane prepared by grafting and plasma polymerization

Ce4+-initiated and plasma-induced grafting polymerization was used to prepare bipolar membranes. The former method used the membrane of copoly(2-hydroxylethylene-methacrylate (2-HEMA)/n-butylacrylate (BA)/glycidyl-methacrylate (GMA)) on the surfaces of which were grafted acrylic acid (AA: COO−) and 4-vinyl pyridine (4VP: NH+Cl−), to prepare the bipolar membrane. The latter method utilized the porous PVDF membrane as a substrate, onto one side of which AA (or sodium vinyl sulfonate, SVS) monomer was grafted, and onto the other of which, 4-vinyl pyridine (or N′,N-dimethyl amino ethyl acrylate, DMAEA) monomer was grafted. The contact angle of bipolar membranes dramatically decreased when the ionic polymer covered the surface of the membranes by plasma-grafting polymerization. Meanwhile, the swelling level of bipolar membranes was in the range of 25–50%. Furthermore, the cross-section SEM photographs of bipolar membranes further illustrated a sandwich structure that consisted of anionic polymer, cationic polymer and PVDF substrate. The limiting current increased with the diffusion coefficient and the concentration of electrolysis; however, the critical voltage was independent of the concentration and the kind of electrolysis. The 963 of AA–PVDF–DMAEA bipolar membrane exhibited the best ratio of dissociation rate constants (kd/kd0) of all membranes. Results concerning the efficiency of the current showed plasma-induced preparation of a bipolar membrane is better than Ce4+-initiated preparation.