Induced-Charge Electro-Osmosis:
Towards Portable Microfluidics

Dr. Todd Squires
Departments of Physics and Applied & Computational Mathematics
California Institute of Technology

Date: Tuesday, February 15, 2005
Time: 4:00 p.m.
Place: Engineering II, Room 3361

ABSTRACT

Microfluidics holds the potential to revolutionize chemistry, biology, and medical devices and diagnostics, much as microchips did for computing, science and technology. The small size of microfluidic devices, and the small sample and reagent volumes they require, are among their frequently-cited advantages. Less often mentioned, however, is the sizeable external machinery -- external pumps, kilovolt electric sources, and so on -- required to drive them. While such machinery may not impede many applications, there are certainly cases where portable and self-contained devices will be required. Toward this goal, I will discuss a nonlinear electrokinetic phenomenon called induced-charge electro-osmosis (ICEO). ICEO arises when an electric field induces an ionic charge cloud around conducting surfaces, and then forces those ions to drive a fluid flow. In contrast with conventional electro-osmosis, ICEO is a nonlinear phenomenon that varies with the square of the applied field. As such, ICEO can be much stronger than conventional electro-osmosis, and allows an appreciable steady flow to be driven even with a modest (~1 Volt) AC potential. Even richer behavior results when spatial symmetries are broken, non-uniform fields are applied, or the potential of the conducting surface itself is manipulated. I will discuss the fundamentals of the phenomenon as well as recent experiments that have verified its key aspects, and will demonstrate how ICEO can be exploited to create elegantly simple microfluidic mixers, high-pressure or low-dispersion pumps, and valves.