Applied Physics

An Umbrella or a Sieve?

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Science  12 Sep 2008:
Vol. 321, Issue 5895, pp. 1419-1421
DOI: 10.1126/science.321.5895.1419d

Modern fabrication techniques can not only produce materials that show strong wetting or repulsion of water or organic liquids, but also offer dynamic control of the wetting behavior in certain cases. Lifton et al. fabricated a silicon membrane with honeycomb-shaped pores, overcoated with a nanonail architecture and an organic self-assembled monolayer or fluoropolymer. Under normal conditions, the membrane repels droplets of water or organic liquids, but after application of a voltage pulse, the droplets undergo an electrowetting transition and the fluid seeps into the pores. For a water droplet, to ensure that the fluid passed through the membrane, the authors placed a hydrophilic glass fiber filter underneath the membrane. They further fabricated a battery in which the tunable membrane keeps the liquid electrolyte and solid electrode separate until a voltage pulse is applied. Because there is no liquid penetration during storage, no electrochemical reactions occur, and so this sort of battery should have an extremely long shelf life. — MSL

Appl. Phys. Lett. 93, 43112 (2008).

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