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Electroosmotic ¯ow (EOF) micropumps which use electroosmosis to transport liquids have been fabricated and used to achieve pressures in excess of 20 atm and ¯ow rates of 3.6 ml/min for 2 kV applied potentials. These pumps use deionized water as working ¯uids in order to reduce the ion current of the pump during operation and increase thermodynamic(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)
—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)
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)
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)
Fiber-based coalescers are widely used to accumulate droplets from aerosols and emulsions, where the accumulated droplets are typically removed by gravity or shear. This Letter reports self-propelled removal of drops from a hydrophobic fiber, where the surface energy released upon drop coalescence overcomes the drop-fiber adhesion, producing spontaneous(More)
Surface energy released upon drop coalescence is known to power the self-propelled jumping of liquid droplets on superhydrophobic solid surfaces, and the jumping droplets can additionally carry colloidal payloads toward self-cleaning. Here, we show that drop coalescence on a spherical particle leads to self-propelled launching of the particle from virtually(More)