Polyaniline doped ultrafiltration membranes: Mechanism of membrane formation and pH response characteristics

Interplay of thermodynamic instability and kinetic effects during formation of polymeric membrane using polyaniline (PANI) as additive are studied along with the pH responsive characterization of the membranes. PANI membranes exhibit pH responsive permeability hysteresis having> 30% variation between the two end points. Effect of pH on mechanical strength, contact angle, surface pore size and roughness, etc was studied in detail. It was observed that PANI molecules shrunk in acidic pH whereas, in alkaline pH, swelling occurred leading to increase in size of PANI molecule from 40 mu m at pH 2-88 mu m at pH 12. Mechanism of membrane pore constriction was proposed based on swelling of PANI in response to pH change and hydrogen bonding. Change in porosity with pH gets reflected by highest rejection of dextran at pH 12 (71%) followed by pH 7 (57%) and pH 2 (50%).