Simple electroosmotic pump and active microfluidics with asymmetrically coated microelectrodes

Abstract

In a microfluidic device, the precisely pumping microliter liquids is one of the critical parts. Micropumping devices have made major advances towards a new platform for the precise control of fluid. It is a long history to use the electric field to transport fluids in the microchannels, which has been one of the most efficient and popular technique tools in thenonmechanical micropumping system. Previously, the alternating current electroosmosis is widely studied in liquid pumping system by applying alternating potential on the pairs of coplanar asymmetrical interdigitated microelectrodes. Here, a much simpler noncoplanar active micropump device is demonstrated. The device is constructed with a sandwich structure including of a microelectrodes array on bottom substrate, a middle microfluidic channel and a top planar electrode. Owing to the halfdepositing of electrodes on the three-dimensional microstructures, an asymmetrical electric field is established around the microelectrodes, which interacts with the electric double layer induced under the applied alternating potential, finally resulting in a net unidirectional pumping flow generated on the device. The pumping ability of this noncoplanar active micropump is successfully verified in the deionized water under applied alternating potential. The equivalent circuit analysis, numerical simulation models of the pumping system and experimental velocity profiles are used to explain the fluid motion mechanism that the bended electric field originated from the asymmetrical electrodes leads to the pumping of fluid in the channel. A series of devices with various electrode structures are prepared to state the structure-dependent pumping performance of this noncoplanar micropump system. A simulated physics value, spatially averaged electric field strength,is defined to evaluate the influence of electric field strength and the density of pumping unit on the final pumping performance, which shows a good consistency with the experimental velocity profiles on a series of devices and offers a feasible way to fast predict and evaluate the pumping performance before processing the real device microfabrication procedures. In addition, it is possible to precisely generate any desired flow pattern on microscopical or macroscopical scale due to the easy preparation process and simple structure of the micropump system. To demonstrate the scalability and flexibility of this design, a microvortex generator and a three channels microfluidics device by integrating multiple pumping segments together are emonstrated. This micropump device can be easily scale up by applying nanoimprint or nanomoulding technique for cheap and fast fabrication, which provides a tool to pump liquids and control fluids at microscopic or macroscopical scale in the complex microfluidics system.