Characterization of the Anisotropic Wetting Property in Liquid Transportation on the Surface With Ratchet Structures

Abstract In this paper, the samples with ratchet structures surface, are set vertically and horizontally in the liquid transportation experiments. Both static and dynamic directional property has been recorded by a high-speed camera. The variation of static contact angles and the shape of the drop in a ratchet structure are measured. The geometric evolutions of drop shed off along different direction on ratchet structure surface and the smooth surface under dynamic condition, are observed for comparison. The advancing contact angle and velocity of drop shed off the ratchet structure are analyzed in detail. The directional liquid transportation mechanism of anisotropic wettability property is demonstrated. Results show that the static drop moves parallel along ridges quickly, and the tooth limit the anisotropic drop spread to the other teeth along the vertical direction, this anisotropic wettability behavior in ratchet structure, which is related to the velocity of liquid transport, the velocity of liquid drop along the backward direction is slower than that of forward direction. The anisotropic wettability property along the horizontal direction of groove limits the transportation ability of the drop. The observed drop deformation includes rotating, rolling, and shaking-induced movements. The surface tension, adhesive behavior, and curvature difference cause the hysteresis effect, which presents a major barrier for liquid transportation.