Abstract:

Natural surfaces with super hydrophobic properties often have micro or hierarchical structures. In this paper, the wetting behaviours of a single droplet on biomimetic micro structured surfaces with different roughness parameters are investigated. A theoretical model is proposed to study wetting transitions. The results of theoretical analysis are compared with those of ex-periment indicating that the proposed model can effectively predict the wetting transition. Furthermore, a numerical simulation based on the meso scale Lattice Boltzmann Method (LBM) is performed to study dynamic contact angles, contact lines, and local velocity fields for the case that a droplet displays on the micro structured surface. A spherical water droplet with r_s = 15 μm falls down to a biomimetic square-post patterned surface under the force of gravity with an initial velocity of 0.01 m•s⁻¹ and an initial vertical distance of 20 μm from droplet centre to the top of pots. In spite of a higher initial velocity, the droplet can still stay in a Cassie state; moreover, it reaches an equilibrium state at t≈17.5 ms, when contact angle is 153.16? which is slightly lower than the prediction of Cassie-Baxter’s equation which gives θ_CB = 154.40?.

Key words: biomimetic, wetting behaviours, roughness surfaces, contact angle, wetting transition