A General Model for Static Contact Angles

Abstract

The problem of contact angle and hysteresis determination has direct implications for engineering applications of wetting, colloid and surface science. Significant technical challenges can arise under real-world operating conditions, because the static contact angle is strongly influenced by contamination at the liquid-solid and liquid-vapor interfaces, chemical aging over long times, and environmental variables such as relative humidity and temperature. Analytical models that account for these real-world effects are therefore highly desirable to guide the rational design of robust applications. This work proposes a unified and simple-to-use model that expands Young's local thermodynamic approach to consider surfaces with topographic features of general geometry and varying degrees of liquid infiltration. The unified model recovers classical wetting limits (Wenzel, Cassie-Baxter, and hemiwicking), accounts for observable intermediate states (e.g., impregnating Cassie), and identifies a new limiting state with potential realizability: a Cassie state accompanied by a precursor film, termed the Inverse Wenzel state.