Achieve equilibrium outside the contact angle hysteresis

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.