Prediction of contact angle for hydrophobic surface fabricated with micro-machining based on minimum Gibbs free energy

Abstract When an interface exists between a liquid and a solid, the angle between the surface of the liquid and the outline of the contact surface is described as the contact angle. The size of the contact angle is the metrics of the hydrophobicity of the surface. The prediction of the contact angle has significant effect on the design of hydrophobic surface and improvement of hydrophobicity. In this paper, a prediction model for contact angle has been proposed based on minimum Gibbs free energy. It considers the effects of unilateral force and area constraints of the droplets. The effect of micro-structural parameters on contact angle has also been investigated. Micro-milling experiments have been conducted to fabricate the hydrophobic surface in order to validate the predictive capability of the contact angle model. Results revealed that the established prediction model could estimate the contact angle of hydrophobic surface. The contact angle could be increased by increasing concave width or reducing convex. The outcome of this research will lead to new methodologies for preparing hydrophobic surfaces with micro-machining technology.