Experimental investigation on water repellency and anisotropic wettability of microgrooved polymer surfaces

Abstract

Simple patterns on a surface can enhance water repellency and simultaneously impose directional wettability. Surfaces exhibiting periodic microscale grooves are examples of such surfaces. Here, we design microgrooved surfaces with three different groove widths and experimentally investigate their impact behaviors on the surfaces. In terms of wetting state, the robustness of water repellency against an impinging droplet is evaluated. Contact angle of a surface alone cannot represent the water repellency against impinging droplets. Surfaces with large contact angles are found to be less water repellent. However, water repellency of a surface depends on its capillary pressure, which resists the wetting state transition. The anisotropic pattern of grooves naturally affects the contact line motion of a droplet, particularly during the spreading and receding phases. Therefore, directional behaviors of the spreading and receding diameter and temporal characteristics were also experimentally examined. Temporal characteristics of smooth surfaces are nearly identical to those in the direction parallel to the grooved surface, while distinctive characteristics were observed in the perpendicular direction. This discrepancy probably originated from the discontinuity of the contact line experienced in the perpendicular direction.