High field asymmetric waveform for ultra-enhanced electroosmotic pumping of porous anodic alumina membranes

Abstract

An electroosmotic EO process is presented for nanoporous membranes capable of generating EO flow rates over thirty times higher than previously possible with the same membrane and solution. In generating high EO flows, a limiting factor is faradaic reactions which appear at high electric fields. A process is presented capable of limiting and even canceling these reactions allowing electric field between one and two orders of magnitude higher. This is achieved by applying an asymmetric bipolar rectangular voltage waveform. The results show the enhanced EO pumping capabilities of membranes under a high electric field asymmetric waveform which prevents gas generation at high voltages. A baseline is established by measuring the EO pump performance when a constant voltage is applied to SiO2-coated nanoporous anodic aluminum oxide membranes. The analysis compares the effect of the applied voltage type on the maximum flow rate, power consumption, and maximum pressure. Results show that large gas generation prevents membrane operation when direct current DC voltages above 50 V are applied. On the other hand, it operates normally under an asymmetric voltage +1,800/−900 V applied, with negligible gas generation. This results in a thirty-time flow rate increase. Larger flow rates/voltages are possible but were not considered due to hardware limitations.