Anders Brask

A novel electro-osmotic pump design for nonconducting liquids: theoretical analysis of flow rate–pressure characteristics and stability

We present the design and theoretical analysis of a novel electro-osmotic (EO) pump for pumping nonconducting liquids. Such liquids cannot be pumped by conventional EO pumps. The novel type of pump, which we term the two-liquid viscous EO pump, is designed to use a thin layer of conducting pumping liquid driven by electro-osmosis to drag a nonconducting working liquid by viscous forces. Based on computational fluid dynamics, our analysis predicts a characteristic flow rate of the order nL/s/V and a pressure capability of the pump in the hPa/V range depending on, of course, achievable geometries and surface chemistry. The stability of the pump is analyzed in terms of the three instability mechanisms that result from shear-flow effects, electrohydrodynamic interactions and capillary effects. Our linear stability analysis shows that the interface is stabilized by the applied electric field and by the small dimensions of the micropump.

Flow reversal at low voltage and low frequency in a microfabricated ac electrokinetic pump.

Microfluidic chips have been fabricated in Pyrex glass to study electrokinetic pumping generated by a low-voltage ac bias applied to an in-channel asymmetric metallic electrode array. A measurement procedure has been established and followed carefully resulting in a high degree of reproducibility of the measurements over several days. A large coverage fraction of the electrode array in the microfluidic channels has led to an increased sensitivity allowing for pumping measurements at low bias voltages. Depending on the ionic concentration a hitherto unobserved reversal of the pumping direction has been measured in a regime, where both the applied voltage and the frequency are low, V(rms)<1.5 V and f<20 kHz , compared to previously investigated parameter ranges. The impedance spectrum has been thoroughly measured and analyzed in terms of an equivalent circuit diagram to rule out trivial circuit explanations of our findings. Our observations agree qualitatively, but not quantitatively, with theoretical electrokinetic models published in the literature.

Theoretical analysis of the low-voltage cascade electro-osmotic pump

The recently published experimental results obtained by Takamura et al. [Y. Takamura, H. Onoda, H. Inokuchi, S. Adachi, A. Oki, Y. Horiike, in: J.M. Ramsey, A. van den Berg (Eds.), Proceedings of the μTAS 2001, Monterey, CA, USA, Kluwer Academic Publishers, Drodrecht, 2001, p. 230], on their low-voltage cascade electro-osmotic pump are analyzed using two different theoretical approaches. One is the semi-analytical equivalent circuit theory involving hydraulic resistances, pressures, and flow rates. The other is a full numerical simulation using computational fluid dynamics. These two approaches give the same results, and they are in good qualitative agreement with the published data. However, our theoretical results deviate quantitatively from the experiments. The reason for this discrepancy is discussed.

The Low-Voltage Cascade EOF PUMP: Comparing Theory with Published Data

The recently published experimental results obtained by Takamura et al. [proc. Micro Total Analysis Systems 2001, p. 230–232 (2001)], on their low-voltage cascade electroosmotic pump are analyzed using two different theoretical approaches. One is the semi-analytical equivalent circuit theory involving hydraulic resistances, pressures, and flow rates. The other is a full numerical simulation using computational fluid dynamics. These two approaches give the same results, and they are in good qualitative agreement with the published data. However, our theoretical results deviate quantitatively from the experiments. The reason for this discrepancy is discussed.

Electroosmotically Driven Two-Liquid Viscous Pump for Nonconducting Liquids

A novel pump design relying on two-liquid viscous drag to pump nonconducting liquids is presented. A conducting pumping liquid driven by electroosmosis (EOF) drags a nonconducting working liquid by viscous forces. In particular liquids such as oil or ethanol, which normally cannot be moved by an EOF, can be pumped through the system. The pump is operated in the low-voltage regime. The flow-rate/pressure (Q-p) characteristic of the pump depends largely on achievable geometrical dimensions. This paper presents a complete theoretical and modeling study of the novel design.