Enhancing AC Electrothermal Micropumping by Integrating Temperature Bias and Surface Modification

Abstract

This paper describes an experimental study of the improvement of bi-directional AC (Alternating Current) electrothermal micropump velocity by a surface modification process and the addition of a temperature bias. The work focuses on exploiting external temperature bias to enhance micropumping by AC electrothermal (ACET) effect. Adding temperature bias to a symmetrical electrode setup provides an advantage of bi-directional characteristic. Here an integrated AC micropump design is proposed, which is expected to solve the problem of on-chip pumping for biofluids. A polymer base nanocomposite coating consisting of a homogeneous mixture of silicon nanoparticles in polydimithylsiloxane (PDMS) is used to improve the hydrophobicity of the micropump surfaces. Due to the hydrophobic nature of PDMS and the monolayer coating with nanoscale surface roughness, the hydrophilic surface of temperature biased ACET micropump will transform to a hydrophobic surface. In addition to hydrophobicity improvement, adding a thin nanocomposite monolayer will physically separate the electrodes from the pumping liquid, thus eliminating their reaction, which is usually observed due to the application of voltage. In addition, the surface modification of micropump will decrease the friction loss and improve the pumping velocity. All experiments were done at 100 kHz VAC that also suppress the bubble generation. As a result, we could apply 7.5 Vrms (equivalent to 21.2 V, peak to peak) voltages to the symmetrical electrode arrays and higher pumping rates (2100 microns/sec) are achieved.