Electrokinetic Phenomena in Organic Solvents

Solid/liquid interfaces play a key role in separation processes, energy storage devices, and transport in nanoscale systems. Nanopores and mesopores with well-defined geometry and chemical characteristics have been a valuable tool to unravel electrochemical properties of interfaces, but the majority of studies have been focused on aqueous solutions. Here, we present experiments and numerical modeling aimed at characterizing effective surface charge of polymer pores in mixtures of water and alcohols as well as in propylene carbonate and acetone. The charge properties of pore walls are probed through analysis of current-voltage curves recorded in the presence of salt concentration gradients. The presence and direction of electro-osmotic flow lead to asymmetric current-voltage curves, with rectification characteristics determined by the polarity of surface charge. The results suggest that the effective surface charge of the pore walls depends not only on the type of solvent but also on the concentration of the electrolyte and voltage. We identified conditions at which polymer pores that are negatively charged in aqueous solutions become positively charged in propylene carbonate and acetone. The findings are of importance for nonaqueous separations, fundamental knowledge on solid/liquid interfaces in organic media, and preparation of porous devices with tunable surface charge characteristics.