AC Electrothermal Effect in Microfluidics: A Review

Abstract

The electrothermal effect has been investigated extensively in microfluidics since the 1990s and has been suggested as a promising technique for fluid manipulations in lab-on-a-chip devices. The purpose of this article is to provide a timely overview of the previous works conducted in the AC electrothermal field to provide a comprehensive reference for researchers new to this field. First, electrokinetic phenomena are briefly introduced to show where the electrothermal effect stands, comparatively, versus other mechanisms. Then, recent advances in the electrothermal field are reviewed from different aspects and categorized to provide a better insight into the current state of the literature. Results and achievements of different studies are compared, and recommendations are made to help researchers weigh their options and decide on proper configuration and parameters.

Numerical simulation of a tuneable reversible flow design for practical ACET devices

“…7 A graph showing how the velocity varies with a voltage applied to the second small electrode, while keeping the first small electrode at 7 V. This differential in voltages from the central ground electrode will cause the field over the electrode to become slightly more symmetrical, both reducing speed and improving mixing. As this relationship follows the curve shown above, this can be used to fine tune the speed of the fluid in the channel with a higher degree of accuracy than simply by changing the input electrode voltage, as has been described in other works [20]…”

“…KCl is chosen as an appropriate simulation material due to its conductivity of a similar magnitude to that of biofluids, and its prevalence in prior reported work for ease of comparison [11]. As the ACET force proportionally increases with fluid conductivity, higher conductivity biofluids (> 1 S/m) will experience higher flow rates [4,20]. Figure 1a-c shows the boundary conditions and new electrode geometry, featuring two thin electrodes adjacent to either side of a wide electrode on both the top and bottom of a microfluidic channel.…”

“…where p represents the pressure vector field, represents dynamic viscosity, u represents the fluid velocity field and F e represents electrothermal force, which is given in time averaged form below [20]. It is important to note that will vary with temperature fluctuations.…”

“…The equation for electrothermal force assumes the change with respect to temperature for electric permittivity, given by α, and conductivity, given by β, are − 0.4% K −1 and 2% K −1 respectively [20].…”

“…This enables precise analytics without the use of large benchtop systems. The AC Electrothermal (ACET) technique has shown high effectiveness in the transport and mixing of conductive biofluids, required for miniaturized lab-on-a-chip systems [3,19,20,25]. Through the production of vortices in the fluid, ACET is also capable of simultaneously mixing and transporting fluids [3,19].…”