Pumping of liquids with traveling-wave electroosmosis

Abstract

Net flow of electrolyte induced by a traveling-wave electric potential applied to an array of microelectrodes is reported. Two fluid flow regimes have been observed: at small-voltage amplitudes the fluid flow follows the direction of the traveling wave, and at higher-voltage amplitudes the fluid flow is reversed. In both cases, the flow seems to be driven at the level of the electrodes. The experiments have been analyzed with a linear electroosmotic model based upon the Debye-Huckel theory of the double layer. The electrical problem for the experimental interdigitated electrode array is solved numerically using a truncated Fourier series. The observations at low voltages are in qualitative accordance with the electroosmotic model.

Traveling-Wave Electrophoresis For Microfluidic Separations

“…satisfying 10 < P < 300, though diffusion might refine predictions of the trapping threshold. Our low frequencies f preclude net electroosmotic pumping of fluid along the microchannel axis [6], but might allow localized circulatory electroosmotic flow (EOF) because ¼ 1=f % 0:1 s is large compared with the characteristic EOF response time EOF ¼ 4h 2 = % 0:0003 s [18]. We intend to study the extent and effects of such flows via models and experiments with uncharged tracer particles.…”

“…In contrast with electron trapping by plasma waves [10], viscosity is essential to TWE trapping. The 1-32 Hz frequencies of our applied potentials are too small to induce ac electroosmotic pumping, which requires frequencies of the order of 1 kHz [6].Models presented here include only electric and Stokes drag forces F E ¼ qE and F D ¼ À6 rv on the ions, ignoring magnetic and gravitational fields, molecular diffusion, charge redistribution, fluid flow, and ionic inertia. Setting F E þ F D ¼ 0 immediately yields the associated electrophoretic velocity…”

“…In contrast with electron trapping by plasma waves [10], viscosity is essential to TWE trapping. The 1-32 Hz frequencies of our applied potentials are too small to induce ac electroosmotic pumping, which requires frequencies of the order of 1 kHz [6].…”

“…This design allows the use of low applied voltages to avoid unwanted electrochemical effects while keeping the electric field high to achieve rapid separations. Singlesurface architectures can also transport charged particles via ac electroosmotic pumping [6,7] and neutral bioparticles via dielectrophoresis [8].We consider the motion of ions of charge q, hydrodynamic radius r, and velocity v through a stationary electrically conducting solution of viscosity and mass density in response to oscillating electric potentials applied to periodic arrays of electrodes. In contrast with studies of oscillator synchronization [9], TWE potentials are external functions of time.…”

“…This design allows the use of low applied voltages to avoid unwanted electrochemical effects while keeping the electric field high to achieve rapid separations. Singlesurface architectures can also transport charged particles via ac electroosmotic pumping [6,7] and neutral bioparticles via dielectrophoresis [8].…”