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Microfluidic mixing utilizing electrokinetic instability stirred by electric potential perturbations in a glass microchannel

LUO WINJET1,* , YARN KAOFENG2, MING-HSYAN SHIH3, KUANG CHENG YU2

Affiliation

  1. Department of Refrigeration, Air Conditioning and Energy Engineering, National Chin-Yi University of Technology, Taiping City, Taichung County 411, Taiwan
  2. Department of Electronic Engineering, Far East University, Tainan 744, Taiwan
  3. Department of Mechanical Engineering, Chinese Military Academy, Fengshan, Taiwan

Abstract

The electrokinetic instability (EKI) phenomenon occurs when microfluidic flows with an electrical conductivity gradient are driven by a high-intensity external electrical field. Although EKI limits the robust performance of complex electrokinetic bioanalytical systems, it can be actively exploited to achieve the rapid mixing of micro- and nanoliter volume solutions in microscale devices. This paper investigates the EKI phenomenon in a T-type glass microchannel, in which two aqueous electrolyte solutions with a 3.5:1 conductivity ratio are driven electrokinetically into the mixing channel via the application of a DC electrical field. It is found that fluctuating, unstable waveforms are formed in the entrance region of the mixing channel and then propagate in the downstream direction when the intensity of the electrical field is increased beyond a certain critical threshold value. Electrical field intensity perturbations aligned in the direction of the conductivity gradient are then added to the DC electrical field at the upper inlet of the T-type glass microchannel. It is found that these perturbations stir the microfluidic instability and antedate the onset of flow instability. Significantly, the application of the electrical field intensity perturbations induces flow instability, and hence improves the mixing efficiency, even when the intensity of the DC electrical field is lower than the critical threshold value.

Keywords

Electrokinetic instability (EKI), Electrical conductivity, Electrical field perturbation, Mixing efficiency.

Citation

LUO WINJET, YARN KAOFENG, MING-HSYAN SHIH, KUANG CHENG YU, Microfluidic mixing utilizing electrokinetic instability stirred by electric potential perturbations in a glass microchannel, Optoelectronics and Advanced Materials - Rapid Communications, 2, 2, February 2008, pp.117-125 (2008).

Submitted at: Jan. 28, 2008

Accepted at: Feb. 11, 2008