22. electrokinetic flow over patterned hydrophobic surfaces
Department: Mechanical & Aerospace Engineering
Research Institute Affiliation: Agile - CaliBaja Center for Resilient Materials & Systems
Faculty Advisor(s): Prabhakar R. Bandaru
Name: Bei Fan
Grad Year: 2020
When salt solution flows over a charged surface in the microchannel, the counter ions will be absorbed to the surface and form an electrochemical double layer (EDL), the thickness of EDL is Debye length. Due to the movement of counter ions in the EDL, the counter ions will accumulate in one of the water reservoir at one end of the channel and produces a potential difference across the channel, which is called streaming potential. That is electrokinetic flow, and can be used as microchannel battery to convert mechanical energy, such as pressure driven flow, to electricity. We also proposed that it can be used on wearable devices as sweat-to-electricity power source. When liquid flows over superhydrophobic surfaces, the imbedded air pockets can prevent the surface getting fully wetted. Because the viscosity of water is much larger than the air viscosity, the liquid-air interface is free of shear stress and yields a finite slip velocity and slip length. In theoretical, the streaming potential is proportional to the slip/Debye length ratio. And this work is inspired by the possible enhancement of streaming potential when liquid flows over charged superhydrophobic surfaces. We made stream wise direction patterned samples with different air fractions to explore the relationship between streaming potential and air fraction. In theoretical, the larger the air fraction, the larger the slip length, and the larger the streaming potential. However, the experiment results are contradictory with the expected results. And we explained this as the lack of charge in the slip areas.
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