Analysis for contact angle hysteresis on rough surfaces by a phase-field model with a relaxed boundary condition

In this paper, we study the contact angle hysteresis on a slowly moving rough boundary using a phase-field model with a relaxed boundary condition. In particular, we want to model the recent experimental observation in [D. Guan et al., Phys. Rev. Lett., 116 (2016), 066102]. The speed of the moving boundary is slow enough so that the fluid flow effect is negligible. From asymptotic analysis, we derive an ordinary differential system for the dynamics of the apparent contact angle and the contact point. The system enables us to understand the contact angle hysteresis in the experiment, including the asymmetric dependence of the advancing and receding contact angles on the boundary velocity.