Characterization and manipulation of the electroosmotic flow in porous anodic alumina membranes

Porous anodic alumina membranes (PAAMs) have uniform and high-density nanopores, and the dimension and interval of the pores can be easily controlled by varying the anodization conditions. The application of PAAMs could widely impact the cost and efficiency of the liquid-based nanoscale separations. We report here the property of electroosmotic flow in PAAMs, which plays a significant role in the mass transport across these membranes that have charged pore surfaces. By controlling the solution pH and the magnitude and sign of the applied current, the mass transport through these nanoporous membranes can be spatially and temporally manipulated. The effects of electrosurface properties and electrolyte ionic strength on electroosmotic flow were studied. The anion incorporation and adsorption cause the variation of the electrosurface properties of PAAMs, which in turn influence the rate and direction of the mass transport. As compared to the membrane with fixed surface charge, this diversity makes it possible for the PAAMs to be used in various conditions.