An electrolysis-based bubble-actuated micropump

Abstract

Micropumps come in a variety of designs that use different actuation mechanisms. Diaphragm micropumps,1 for example, achieve high volume through a large chamber using a membrane: however, most techniques for fabricating such diaphragm-based pumps are complicated and involve many photolithographic steps. Another technique2, 3 drives fluid by applying a high voltage to it. Among such approaches, bubbleactuated valveless micropumps are attractive for their simple operation, miniaturized size, large actuation force, and the ability to conform physically to different types of microchannels with a wide range of cross-sections. Unfortunately, although these valveless pumps have been successfully demonstrated,4–6 they involve complicated time-sequence power control on many pairs of electrodes, large or long nozzle-diffuser structures, and have the further disadvantage of a sealed reservoir inside the fluidic chip. To overcome these problems, we propose a compact micropump with a simple pattern of changing surface roughness (i.e., gradient) to propel the liquid forward. Like other valveless micropumps, our device has a large actuation force. But it has the additional benefits of low power consumption and room temperature operation. It also gets around the sticking or choking of electrolytic bubbles that happens with sealed reservoirs. Figure 1(a) illustrates the design concept. The device consists of platinum electrodes, a hydrophilic microchannel, and a hydrophobic lateral breather connected to air for removing bubbles. The pumping principle—shown schematically from the side in Figure 1(b)—relies on surface tension and multiple bubble-actuation cycles. The actuation mechanism is divided into three phases: bubble generation, degassing, and liquid movement. First, the bubble is generated by electrolysis to push the liquid inwhichever direction is required. Next, the bubble is vented out through the lateral breather. At the sides of the microchannel, surface tension exerts a pull on the liquid that creates a characteristic concave shape called a meniscus. Owing to Figure 1. Schematic illustration of the design concept and pumping principle. (a) A three-dimensional view of the micropump. (b) A side view showing net pumping flow along the x direction in the three phases of a single pumping cycle. Here, PL and PR represent pressure. θL, θR, and θb are contact angles.