Abstract
In this work, we focus on investigating electrothermal flow in rotating electric fields (ROT-ETF), with primary attention paid to the horizontal traveling-wave electrothermal (TWET) vortex induced at the center of the electric field. The frequency-dependent flow profiles in the microdevice are analyzed using different heat transfer models. Accordingly, we address in particular the importance of electrode cooling in ROT-ETF as metal electrodes of high thermal conductivity, while substrate material of low heat dissipation capability is employed to develop such microfluidic chips. Under this circumstance, cooling of electrode array due to external natural convection on millimeter-scale electrode pads for external wire connection occurs and makes the internal temperature maxima shift from the electrode plane to a bit of distance right above the cross-shaped interelectrode gaps, giving rise to reversal of flow rotation from a typical repulsion-type to attraction-type induction vortex, which is in good accordance with our experimental observations of co-field TWET streaming at frequencies in the order of reciprocal charge relaxation time of the bulk fluid. These results point out a way to make a correct interpretation of out-of-phase electrothermal streaming behavior, which holds great potential for handing high-conductivity analytes in modern microfluidic systems.
Highlights
The rapid advance of lab-on-chip technology requires the exploitation of new approaches capable of achieving precise fluid actuation and manipulation at the micrometer scale [1,2,3,4]
First and foremost, we experimentally observed the performance of driving rotating electric fields (ROT-ETF) in our device and discovered that the central out-of-phase traveling-wave electrothermal (TWET) whirlpool above the cross-shaped interelectrode gaps rotates in the direction of signal-phase propagation, which violates the actuation of anti-field induction EHD on a glass base predicted by previous researchers [42]
It is discovered that the central out-of-phase TWET whirlpool above the cross-shaped interelectrode gaps rotates in the direction of signal-phase propagation, which violates the actuation of anti-field induction EHD on a glass base predicted by previous researchers [42]
Summary
The rapid advance of lab-on-chip technology requires the exploitation of new approaches capable of achieving precise fluid actuation and manipulation at the micrometer scale [1,2,3,4]. Different from the conventional linear TW array, electrodes of opposite phases are positioned right against one another with quite small space intervals in this circulating electrode design, so both SWET and TWET appear and actively compete against one another within a broad frequency range, which brings additional richness to existing ACET techniques [41] It would be of particular interest and great benefit to study the behavior of electrothermal flow in rotating electric fields (ROT-ETF) where both in-phase and out-of-phase polarizations occur and vary as a function of applied field frequency. These unique characterizations of our electrothermal microdevice, including both the rotation and pump motions of microfluidics under the effect of electrode cooling, ingeniously provide new insights into tackling major issues that involve on-chip operations at low temperatures, such as conducting chemical reaction [43], drug delivery [44] and cell culture [45] in the context of high-conductivity buffer solutions for modern micro total analytical systems
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
