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.