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Size-selective sliding of sessile drops on a slightly inclined plane using low-frequency ac electrowetting SCIE SCOPUS

Title
Size-selective sliding of sessile drops on a slightly inclined plane using low-frequency ac electrowetting
Authors
Jiwoo HongSeung Jun LeeBonchull Chris KooYong Kwon SuhKang, KH
Date Issued
2012-04-17
Publisher
AMER CHEMICAL SOC
Abstract
When placed on an inclined solid plane, drops often stick to the solid surface due to pinning forces caused by contact angle hysteresis. When the drop size or the plane's incline angle is small, the drop is difficult to slide due to a decrease in gravitational force. Here we demonstrate that small drops (0.4-9 mu L) on a slightly inclined plane (similar to 12 degrees, Teflon and parylene-C surface) can be mobilized through patterned electrodes by applying low-frequency ac electrowetting under 400 Hz (110-180 V-rms), which has a mechanism different from that of the high-frequency ac method that induces sliding by reducing contact angle hysteresis. We attribute the sliding motion of our method to a combination of contact angle hysteresis and interfacial oscillation driven by ac electrowetting instead of the minimization of contact angle hysteresis at a high frequency. We investigated the effects of ac frequency on the sliding motion and terminal sliding of drops; the terminal sliding velocity is greatest at resonance frequency. Varying the electrowetting number (0.21-0.56) at a fixed frequency (40 Hz) for 5 mu L drops, we found an empirical relationship between the electrowetting number and the terminal sliding velocity. Using the relationship between the drop size and ac frequency, we can selectively slide drops of a specific size or merge two drops along an inclined plane. This simple method will help with constructing microfluidic platforms with sorting, merging, transporting, and mixing of drops without a programmable control of electrical signals. Also, this method has a potential in heat transfer applications because heat removal capacity can be enhanced significantly through drop oscillation.
Keywords
CONTACT-ANGLE HYSTERESIS; HEAT-TRANSFER; LIQUID-DROPS; HETEROGENEOUS SURFACES; GRADIENT SURFACES; MOTION; ACTUATION; VIBRATION; OSCILLATION; DROPLETS
URI
https://oasis.postech.ac.kr/handle/2014.oak/16590
DOI
10.1021/LA2039703
ISSN
0743-7463
Article Type
Article
Citation
LANGMUIR, vol. 28, no. 15, page. 6307 - 6312, 2012-04-17
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강관형KANG, KWAN HYOUNG
Dept of Mechanical Enginrg
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