Study of transporting of droplets on heterogeneous surface structure using the lattice Boltzmann approach

Droplet movement on heterogeneous surfaces was simulated with a computational fluid dynamics (CFD) modeling method known as the lattice Boltzmann method (LBM). Motions of droplets were also analyzed in terms of kinetic, gravitational, and surface free energy. The first part of this study focused on the transportation of droplets by chemical actuation on a surface divided by five chemical bends, each having a different hydrophobicity, establishing a gradual progression from hydrophobic to hydrophilic phases. The second part of this study focused on the transportation of droplets by a surface with a structural gradient having its two halves textured with microscopic pillars, corresponding to a difference in hydrophobicity. In the first part of the study, the numerical results showed that a droplet tended to move to a less hydrophobic region with surface free energy reduction by spreading and decaying. This indicates that the surface free energy was converted into kinetic energy and gave mobility to the droplet. In the second part, three steps of the droplet motion were observed: spreading, recoiling, and translation.