High-flowrate, compact electroosmotic pumps with porous polymer track-etch membranes

This paper reports the experimental investigations of electroosmotic (EO) pumps with four types of porous polymer membranes: porous polycarbonate track-etch membranes, porous polyester track-etch membranes, mixed cellulose ester membranes, and nylon membranes. We characterized EO pumping performance using deionized (DI) water and 1 mM sodium tetraborate buffer in terms of flowrate and current. The measured flowrate and current show a linear dependency on an applied voltage, as expected by theory. The increasing order of both the parameters is polycarbonate, polyester, mixed cellulose ester, and nylon for both DI water and buffer. We compared EO pumping with porous polymer membranes to that with porous glass as a benchmark in terms of the flowrate normalized by the pumping area and applied voltage and flowrate per current. The experiments show that porous polymer membranes excel over porous glass in most cases. From the results about flowrate per current, we can estimate that the zeta potential of most porous polymer membranes used in this paper is greater than that of porous glass. The best performance was found with polycarbonate track-etch membranes as 0.051 ml V−1 cm−2 with buffer and 2.4 ml min−1 mA−1 with DI water. The normalized flowrate with DI water is 0.016 ml V−1 cm−2, which is lower than the previously reported value with porous anodic alumina membranes. Porous polymer membranes however have the advantages of membrane flexibility and excellent bonding with other polymeric structures, compared with porous anodic alumina membranes. We demonstrated a miniature 2 cm3 EO pump by taking the advantage of the flexible characteristics. This EO pump has a cylindrical shape with a large pumping area per pump volume, which is beneficial for miniaturization. The miniature EO pump shows good pumping performance in our short-term experiments (less than 10 min).