Tunable Surfaces

In a new experiment conducted at Bell Labs/Lucent, a liquid drop was maneuvered around a special surface consisting, at the microscopic level, of a forest of tiny stalks. The blades of this "nanograss" can be selectively electrified so as to move the drop from place to place or to cause it to lose its spherical shape and to wet the surface below.

Lucent scientist Tom Krupenkin, also speaking at the APS meeting, said that the conversion of the surface from hydrophobic (the drop staying aloof at the top of the blades) to hydrophilic (the drop collapsing and flooding the plain between the blades) could result in many potential applications.

Heat mitigation is one example. Drops could be delivered to hot spots on microchips, where the drop could douse the troubled area (sort of like an airborne drop of water during forest fires), absorb the heat, and then depart. Optical properties of a surface could be switched from one state to another through electronically controlled wetting.

Microfluidics applications include combinatorial chemistry in microreactors, drag reduction, or altering the friction of channels. In microbatteries, electrochemicals could be kept isolated until energy was actually needed, thus extending the battery's working life and saving energy for moments of peak activity. (Paper Y22.6)