Characterizing Membrane Surface Charge by Contact Angle Titration

ABSTRACT Accurate characterization of membrane surface charge is vital for understanding membrane surface chemistry, separation performance, and fouling resistance. Streaming potential is the standard electrokinetic phenomena used to characterize a membrane’s isoelectric point and zeta potential, which is related to the dynamic charge functionality at the membranesolution interface as function of solution pH and ionic composition. We have recently developed a new method for directly measuring membrane surface charge via direct surface titration. Direct surface titration enables identification of maximum surface charge density, fractional ionization as a function of pH, and the apparent pKa of a charged surface. We have employed this new characterization technique to assess the charge of several commercial polyamide reverse osmosis membranes and compare these results to charge determined from classical electrokinetic measurements.