Achieve equilibrium outside the contact angle hysteresis

TL;DR

This paper challenges the traditional view by deriving conditions under which the equilibrium contact angle can be outside the usual hysteresis range, reaching zero on super-hydrophilic surfaces, supported by theoretical and experimental evidence.

Contribution

It introduces a new understanding of contact angle equilibrium, showing it can be smaller than receding angles and reach zero, contrary to common beliefs.

Findings

Equilibrium contact angles can be smaller than receding angles.

On super-hydrophilic surfaces, equilibrium can reach 0 degrees.

Theoretical, numerical, and experimental results confirm these findings.

Abstract

It is common belief that the equilibrium contact angle, corresponding to the minimum system energy state, lies between advancing and receding contact angles. Here, we derive advancing and receding contact angles considering the micro contacting processes on ideal rough 2D surfaces. Equilibrium contact angles obtained via energy minimization can be smaller than the receding contact angle and reach 0 degrees, at which hysteresis diminishes on the super-hydrophilic surface. Gibbs free energy analyses, numerical simulations and physical experiments all confirm these new findings.