Enhanced electro-osmosis in propylene carbonate salt solutions

Properties of solid-liquid interfaces and surface charge characteristics mediate ionic and molecular transport through porous systems, affecting many processes such as separations. Herein, we report experiments designed to probe the electrochemical properties of solid-liquid interfaces using a model system of a single polyethylene terephthalate (PET) pore in contact with aqueous and propylene carbonate solutions of LiClO₄. First, the existence and polarity of surface charges were inferred from current-voltage curves recorded when a pore was placed in contact with a LiClO₄ concentration gradient. Second, the electro-osmotic transport of uncharged polystyrene particles through the PET pore provided information on the polarity and the magnitude of the pore walls' zeta potential. Our experiments show that the PET pores become effectively positively charged when in contact with LiClO₄ solutions in propylene carbonate, even though in aqueous LiClO₄, the same pores are negatively charged. Additionally, the electro-osmotic velocity of the particles revealed a significantly higher magnitude of the positive zeta potential of the pores in propylene carbonate compared to the magnitude of the negative zeta potential in water. The presented methods of probing the properties of solid-liquid interfaces are expected to be applicable to a wide variety of solid and liquid systems.