Dynamic wetting on superhydrophobic surfaces: Droplet impact and wetting hysteresis
Author(s)Smyth, Katherine M.; Paxson, Adam T.; Kwon, HyukMin; Deng, Tao; Varanasi, Kripa K.
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We study the wetting energetics and wetting hysteresis of sessile and impacting water droplets on superhydrophobic surfaces as a function of surface texture and surface energy. For sessile drops, we find three wetting regimes on these surfaces: equilibrium Cassie at small feature spacing, equilibrium Wenzel at large feature spacing, and an intermediate state at medium feature spacing. We observe minimum wetting hysteresis not on surfaces that exhibit Cassie wetting but rather on surfaces in the intermediate regime. We argue that droplets on these surfaces are metastable Cassie droplets whose internal Laplace pressure is insufficient to overcome the energy barrier required to homogeneously wet the surface. These metastable Cassie droplets show superior roll-off properties because the effective length of the contact line that is pinned to the surface is reduced. We develop a model that can predict the transition between the metastable Cassie and Wenzel regimes by comparing the Laplace pressure of the drop to the capillary pressure associated with the wetting-energy barrier of the textured surface. In the case of impacting droplets the water hammer and Bernoulli pressures must be compared with the capillary pressure. Experiments with impacting droplets show very good agreement with this simple pressure-balance model.
DepartmentMassachusetts Institute of Technology. Department of Mechanical Engineering
Proceedings of the 12th IEEE Intersociety Conference on Thermal and Thermomechanical Phenomena in Electronic Systems (ITherm), 2010
Institute of Electrical and Electronics Engineers
Smyth, Katherine et al. “Dynamic Wetting on Superhydrophobic Surfaces: Droplet Impact and Wetting Hysteresis.” in Proceedings of the 12th IEEE Intersociety Conference on Thermal and Thermomechanical Phenomena in Electronic Systems (ITherm), IEEE, 2010. 1–8. Web.
Final published version
INSPEC Accession Number: 11404004