Document Type : VSI: Membr. for Develop.&Sustain.
Department of Chemistry, Division of Science and Technology, University of Education, Lahore 44770, Pakistan
Department of Chemistry, Khwaja Fareed University of Engineering and Information Technology, Rahim Yar Khan, Pakistan
Department of Chemistry, University of Sahiwal, Sahiwal, Pakistan
Department of Chemistry, School of Natural Sciences, National University of Sciences and Technology, Islamabad, Pakistan
Department of Chemistry, Lahore Garrison University, DHA Phase VI, Lahore, Pakistan
Department of Chemistry, Kohsar University, Murree 47150, Punjab, Pakistan
Ultrathin anion-exchange films have been created by employing layer-by-layer (LBL) deposition method. The LBL deposited protonated poly(allylamine) (PAH)/poly(4-styrenesulfonate) (PSS) polyelectrolyte multilayers (PEMs) behave as anionexchange films when PAH and PSS polyelectrolyte solutions are prepared in NaSCN as a supporting electrolyte (SE). Reflectance FTIR studies indicate that when PAH is prepared in 0.5 M NaSCN and PSS is prepared in 1 M NaSCN, the thickness of the film and the number of anion-exchange sites in the film are manifold greater than those in the film fabricated from PAH and PSS polyelectrolytes when either of them is prepared in 0.5 M NaSCN. Transmembrane potential measurements were performed to measure the permselectivity of thus fabricated PEMs. These measurements indicate that the fabricated films demonstrate high anion-exchange properties at neutral pH. However, the ion-exchange character of the films switches from anions- to cations-exchange when pH of the surrounding solutions changes from 7 to 8.4. Diffusion dialysis results through the coated alumina membranes confirm such a change in the net charge of the films with a change in the pH. Current density-voltage curve studies indicate plenty of formation of H+ and OHions through water dissociation occurring at the interfacial bipolar junction created by depositing these anion-exchange coatings on Nafion cation-exchange membrane (CEM). Donnan dialysis studies also indicate the formation of bipolar junction through deposition of such films on cationexchange membranes.