Surface modification of nano-porous anodic alumina membranes and its use in electroosmotic flow

This study examines the surface-modification effects of porous anodic alumina membranes (PAAMs) on the performance of electroosmotic (EO) pumping. The modifications include using H2O2-pretreated, and followed by 3-aminopropyltriethoxysilane (APS) or 3-mercaptopropyl trimethoxysilane (MPTS) sol–gel solutions to functionalize the surface of PAAM for achieving higher surface charge density. The surface-modified membranes are analyzed by average pore size, contact angle, and FTIR measurements. The results show that APS and MPTS are successfully coated on the surface of PAAMs. The characteristics (e.g., total current, maximum pressure, and normalized flow rate) of the EO pumps with these surface-modified PAAMs are investigated. The comparison results of total current at zero time confirmed that the surface charge density of the surface-modified PAAM has been increased. Consequently, the maximum normalized flow rate of EO pump with the APS- and MPTS-coated PAAM are higher than that with the bare PAAM in DI water but without buffer control methods. The convection current of EO flow is also investigated, and the results show that its contribution to total current is around 11% and thus cannot be ignored for EO flow with nano-size channels.