Abstract
Liquid pumping can occur along the outer surface of an electrode under a DC electric field. For biological applications, a better understanding of the ionic solution pumping mechanism is required. Here, we fabricated CNT wire electrodes (CWEs) and tungsten wire electrodes (TWEs) of various diameters to assess an ionic solution pumping. A DC electric field created by a bias of several volts pumped the ionic solution in the direction of the negatively biased electrode. The resulting electro-osmotic flow was attributed to the movement of an electric double layer near the electrode, and the flow rates along the CWEs were on the order of picoliters per minute. According to electric field analysis, the z-directional electric field around the meniscus of the small electrode was more concentrated than that of the larger electrode. Thus, the pumping effect increased as the electrode diameter decreased. Interestingly in CWEs, the initiating voltage for liquid pumping did not change with increasing diameter, up to 20 μm. We classified into three pumping zones, according to the initiating voltage and faradaic reaction. Liquid pumping using the CWEs could provide a new method for biological studies with adoptable flow rates and a larger ‘Recommended pumping zone’.
Highlights
Liquid pumping can occur along the outer surface of an electrode under a DC electric field
When a DC electric field was applied between two electrodes dipped into an ionic solution, liquid was pumped along the electrode having a negative bias
The liquid pumping of an ionic solution is caused by the movement of mobile ions (EDL) gathered around the electrode, and the resulting flow is the electro-osmotic flow (EOF)
Summary
CWEs and sharpened TWEs having various diameters were fabricated to study liquid pumping of an ionic solution. When a DC electric field was applied between two electrodes dipped into an ionic solution, liquid was pumped along the electrode having a negative bias. The liquid pumping of an ionic solution is caused by the movement of mobile ions (EDL) gathered around the electrode, and the resulting flow is the EOF. The liquid pumping of an ionic solution for biological studies should be applied within the ‘R. pumping zone’ to prevent faradaic reactions. Similar to the Helmholtz-Smoluchowski slip velocity, the flow rate of the transported liquid was linearly proportional to the applied voltage, and inversely proportional to the distance between the two electrodes. We anticipate that the CWEs could provide new devices for biological studies to manipulate liquid with adaptable flow rates
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