Three-dimensional lattice Boltzmann simulations of microdroplets including contact angle hysteresis on topologically structured surfaces

摘要

In this study, the dynamical behavior of a droplet on topologically structured surface is investigated by using a three-dimensional color-gradient lattice Boltzmann model. A wetting boundary condition is proposed to model fluid-surface interactions, which is advantageous to improve the accuracy of the simulation and suppress spurious velocities at the contact line. The model is validated by the droplet partial wetting test and reproduction of the Cassie and Wenzel states. A series of simulations are conducted to investigate the behavior of a droplet when subjected to a shear flow. It is found that in Cassie state, the droplet undergoes a transition from stationary, to slipping and finally to detachment states as the capillary number increases, while in Wenzel state, the last state changes to the breakup state. The critical capillary number, above which the droplet slipping occurs, is small for the Cassie droplet, but is significantly enhanced for the Wenzel droplet due to the increased contact angle hysteresis. In Cassie state, the receding contact angle nearly equals the prediction by the Cassie relation, and the advancing contact angle is close to 180, leading to a small contact angle hysteresis. In Wenzel state, however, the contact angle hysteresis is extremely large (around 100). Finally, high droplet mobility can be easily achieved for Cassie droplets, whereas in Wenzel state, extremely low droplet mobility is identified. (C) 2016 Elsevier B.V. All rights reserved.