Chuan-Hua Chen

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Electrokinetic flow is leveraged in a variety of applications, and is a key enabler of on-chip electrophoresis systems. An important sub-class of electrokinetic devices aim to pump and control electrolyte working liquids with spatial gradients in conductivity. These high-gradient flows can become unstable under the application of a sufficiently strong(More)
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Electroosmotic (EO) micropumps use field-induced ion drag to drive liquids and achieve high pressures in a compact design with no moving parts. An analytical model applicable to planar, etched-structure micropumps has been developed. This model consists of pressure and flow relations in addition to an analytical expression that can be used to estimate the(More)
Electrokinetic flow instabilities occur under high electric fields in the presence of electrical conductivity gradients. Such instabilities are a key factor limiting the robust performance of complex electrokinetic bio-analytical systems, but can also be exploited for rapid mixing and flow control for microscale devices. This paper reports a representative(More)
In conventional dropwise condensation on a hydrophobic surface, the condensate drops must be removed by external forces for continuous operation. This Letter reports continuous dropwise condensation spontaneously occurring on a superhydrophobic surface without any external forces. The spontaneous drop removal results from the surface energy released upon(More)
A lotus leaf retains water repellency after repeated condensation in nature but becomes sticky to water drops after condensation on a fixed cold plate. Our experiments show that mechanical vibration can be used to overcome the energy barrier for transition from the sticky Wenzel state to the nonsticking Cassie state, and the threshold for the dewetting(More)
Electroosmotic flow (EOF) pumps with flow rates on the order of 1 ml/min have been designed and fabricated. These pumps use EOF to propel liquid solutions in a compact system with no moving parts. The pumping chamber is filled with densely packed non-porous silica particles, and the particle bed is held in place using two polymeric porous frits. The pump(More)
The self-cleaning function of superhydrophobic surfaces is conventionally attributed to the removal of contaminating particles by impacting or rolling water droplets, which implies the action of external forces such as gravity. Here, we demonstrate a unique self-cleaning mechanism whereby the contaminated superhydrophobic surface is exposed to condensing(More)
Many natural superhydrophobic structures have hierarchical two-tier roughness which is empirically known to promote robust superhydrophobicity. We report the wetting and dewetting properties of two-tier roughness as a function of the wettability of the working fluid, where the surface tension of water/ethanol drops is tuned by the mixing ratio, and compare(More)
Xiaopeng Qu, Jonathan B. Boreyko, Fangjie Liu, Rebecca L. Agapov, Nickolay V. Lavrik, Scott T. Retterer, James J. Feng, C. Patrick Collier, and Chuan-Hua Chen Department of Mechanical Engineering and Materials Science, Duke University, Durham, North Carolina 27708, USA Center for Nanophase Materials Sciences, Oak Ridge National Laboratory, Oak Ridge,(More)