Controlling and/or improving the surface properties of nanofiltration (NF) membranes and in understanding its role in membrane performance. The role of surface properties is especially critical in NF membranes where rejection is dependent on either steric (size) or electrostatic (charge) factors. NF membranes are capable of rejecting divalent ions and small organic molecules with molecular weight values as low as 300 Da. Applications range from water treatment to purification of biological samples for enhanced sensitvity in biosensors.

We present results of our efforts to control and improve charge density and hydrophilicity of NF membranes via three separate techniques and to characterize by various methods. The first method was the spin casting and wet inversion of varying concentrations of cellulose acetate yielding membranes with various MWCO values and zeta potential profiles. Another method was the formation of a nanofiltration polyamide (PA) thin film by interfacial polymerization on an ultrafiltration (UF) membrane, using reactants chosen to improve the charge density and hydrophilicity of the active PA layer. Characterization results are presented from EKA (Electrokinetic Analysis), AFM, SEM, tangential flow dialysis, and pressure-driven flux and salt rejection performance. In addition, the effect of solute interactions and membrane properties on rejection of mixed ion solutions is presented and The Donnan Steric Pore (DSP) Model is applied to the salt rejection studies to yield effective charge density values.