Bell Labs researcher Ryan Enright and former colleagues at the Massachusetts Institute of Technology (MIT) discovered something quite unexpected in the course of their collaboration on thermal management. As microscopic water droplets leaped away from superhydrophobic surfaces, they assumed an electrical charge. This phenomenon had never previously been observed, and the ramifications could be significant. Ryan, along with co-authors Nenad Miljkovic, Evelyn Wang and Daniel Preston published their findings in the science journal Nature Communications .
The team was exploring the process in which water negotiates the surface of metals with coatings designed to repel water. Under certain circumstances, rather than simply dropping vertically and separating from a surface due to gravity, droplets can actually jump away from it. We see this behavior when droplets of water have condensed on the surface and form an electric double layer (a layer of paired positive and negative charges). When droplets combine, the jumping happens quite rapidly, and consequently the charge separates, leaving some charge on the surface and some on the droplets.
The jumping behavior of droplets from a superhydrophobic condenser surface had been known and researchers at Bell Labs and elsewhere were exploring how that behavior could be used to increase the efficiency of thermal management in various devices and systems. The discovery of the associated charge behavior, however, offers new and potentially significant ways to improve on that efficiency. Thermal management is becoming a critical path factor for sustainable progress in Information and Communication Technology (ICT) as ever-more demanding chip designs at the nanometer level increasingly yield self-destructive heat.
Other dimensions of these findings might lead to greater discoveries and solutions. Jumping droplets with charge could be harnessed for generating power, e.g., from condensation in the ambient air. In this way, surface cooling might be achieved by means of natural water systems (lakes, rivers, etc.) That, however, remains a subject for further exploration.