Actuating Water Droplets on Graphene via Surface Wettability Gradients
QC Liu and BX Xu, LANGMUIR, 31, 9070-9075 (2015).
A surface wettability gradient can break the equilibrium status of a liquid droplet and drives its unidirectional movement on the surface. We propose a conceptual design of the driving water droplet on a graphene surface and demonstrate that both speed and direction of the movement can be controlled via a continuous gradient of surface wettability using comprehensive molecular dynamics (MD) simulations. Controlling the water droplet toward linear and nonlinear arc paths is exemplified in one- and two-dimensional gradients of surface wettability, respectively. Unbalanced Young's equation is extended to understand the speed of the droplet movement, and the predications agree well with MD simulations.
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