Konrad Rykaczewski, Ph.D.
MIT & NIST
Development of Ultrahydrophobic Surfaces for Enhanced Condensation
Development of passive ways to enhance water condensation rate could dramatically improve the energy efficiency of power generation and water desalination. The rate of this phase change process is limited by how quickly condensate can depart the surface. For example, the condensation rate is significantly higher during condensation on hydrophobic surfaces, which promote formation of easily shedding droplets, than on hydrophilic surfaces promoting water film formation (i.e. dropwise vs. filmwise condensation mode). On vertically inclined flat hydrophobic surfaces drops with diameters larger than the capillary length (2.7 mm) can slide off the surface due to gravity. In contrast, on properly designed nanostructured superhydrophobic surfaces even microscale droplets can depart the surface via spontaneous droplet motion. Although various such surfaces have been reported, their development has been fortuitous, not driven by an understanding of the underlying physical processes. In this project we performed a comprehensive study of microscale water condensation dynamics on nanostructured superhydrophobic surfaces made using a variety of synthetic methods. We related surface topography to individual droplet growth mechanism and occurrence of the spontaneous drop motion after coalescence. We used the new fundamental insight from this work to develop quantitative design guidelines for superhydrophobic surfaces intended for condensation applications.