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Light-actuated electrothermal microfluidic motion: experimental investigation and physical interpretation

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Abstract

This paper experimentally investigates a light-actuated electrothermal (ET) flow generated by the simultaneous application of a uniform AC electric field and a focused laser and provides a detailed physical interpretation of the results based on electrokinetic theory. The ET flow is driven in deionized (DI) water in a microfluidic chip consisting of two parallel-plate electrodes and analyzed using flow visualization, particle image velocimetry and single dye-based laser-induced fluorescence thermometry. Our experimental observation and measurement find that the electrothermally induced fluid motion takes the form of a rotationally symmetric toroidal vortex. The toroidal ET vortex shows a source pattern over the electrode surface where the focused laser is located, when the applied AC electric signal is less than the charge relaxation frequency of the DI water. Focusing a laser alternately to each of the two parallel-plate electrodes reveals the forced convection nature of an ET flow. The gradual increase of temperature and applied electric potential in the DI water causes a linear and parabolic increase of the ET velocity, respectively. The increase of AC frequency leads to a rapid decrease of the flow strength. The relative size of natural convection in the ET flows is less than 10 % for most of the applied experimental conditions, but increases up to about 35 % in the AC frequency region above the liquid charge relaxation frequency. From this investigation, it is found that the transition between the two flows occurs for system characteristic lengths around 1.2 mm.

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Correspondence to Steven T. Wereley.

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Kwon, J., Wereley, S.T. Light-actuated electrothermal microfluidic motion: experimental investigation and physical interpretation. Microfluid Nanofluid 19, 609–619 (2015) doi:10.1007/s10404-015-1587-z

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Keywords

  • Particle Image Velocimetry
  • Natural Convection
  • Microfluidic Chip
  • Particle Image Velocimetry Measurement
  • Applied Electric Potential