Electroosmotic pumping has been extensively used in lab-on-a-chip devices and micropumps for microelectronic cooling. High flow rate per unit area with a low applied voltage is a key performance requirement to achieve compact design and efficient operation. In this paper, we report work on using SiO_2-coated porous anodic alumina membranes for high flow rate electroosmotic pumping under low applied voltages. High quality porous alumina membranes of controllable pore diameters in the range of 30-100 nm and pore lengths of 60-100 mu m were fabricated by electrochemical anodization. The pores are straight, uniform and hexagonally close-packed with a high porosity of up to 50 percent of the total area. The inner surface of the pore was coated conformally with a thin layer (approx 5 nm) of SiO_2 to achieve a high zeta potential. The electroosmotic pumping performance of the fabricated anodic alumina membranes, coated and uncoated, was investigated using standard relevant aqueous electrolyte buffer solutions. The high zeta potential of the SiO_2 coating increases the pumping flow rate even though the coating reduces the porosity of the membrane. Results show that nanostructured SiO_2-coated porous anodic alumina membranes can provide a normalized flow rate of 0.125 ml min~(-1) V~(-1) cm~(-2) under a low effective applied voltage of 3 V. This compares favourably with other microporous materials such as glass frits.
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机译：电渗泵浦已广泛用于芯片实验室设备和微泵中，用于微电子冷却。每单位面积的高流量和较低的施加电压是实现紧凑型设计和高效运行的关键性能要求。在本文中，我们报告了在低外加电压下使用SiO_2涂层多孔阳极氧化铝膜进行高流量电渗泵送的工作。通过电化学阳极氧化制备孔径可控制在30-100nm范围内且孔径为60-100μm的高质量多孔氧化铝膜。孔是直的，均匀的并且六角形密堆积，具有高达总面积的50％的高孔隙率。孔的内表面共形地涂覆有SiO_2薄层（约5 nm），以实现高Zeta电位。使用标准的相关电解质水溶液缓冲液，研究了已涂覆和未涂覆的阳极氧化铝膜的电渗泵浦性能。即使涂层降低了膜的孔隙率，SiO_2涂层的高ζ电位也增加了泵送流速。结果表明，纳米结构的SiO_2包覆的多孔阳极氧化铝膜在3 V的低有效施加电压下可以提供0.125 ml min〜（-1）V〜（-1）cm〜（-2）的归一化流量。有利地与其他微孔材料如玻璃粉一起使用。
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