Biphilic jumping-droplet condensation

Abstract

Jumping-droplet condensation on rough superhydrophobic surfaces exhibits increased heat-transfer rates when compared with dropwise condensation on smooth hydrophobic surfaces. However, the performance of superhydrophobic surfaces is limited by the low individual droplet growth rates associated with their extreme apparent advancing contact angles. Here, we report that biphilic surfaces having smooth, low-surface-energy spots on a superhydrophobic background exhibit a 10× higher jumping-droplet condensation heat-transfer coefficient when compared with homogeneous superhydrophobic surfaces. Our detailed condensation heat-transfer modeling coupled with numerical simulations of binary and coordinated droplet coalescence show that spot wettability should not be optimized toward minimizing droplet nucleation energy barriers. Rather, spot wettability should be optimized to minimize droplet adhesion while maximizing individual droplet growth rates. Model-predicted design optimization of a variety of biphilic surfaces is validated against experiments. Our findings provide design guidelines for biphilic surface development to maximize condensation heat transfer.