Interface Deformation Neat the Moving Contact Line on a Periodically Roughened Surface

The dynamic contact angle on non-ideal solid surface generally deviates from the theoretical predictions (e.g. Voinov(Fluid Dyn. 1976), Cox (J. Fluid. Mech., 1985)). In the present study effect of the repetition of the defect on the dynamic contact angle is investigated. The defects are simulated by periodically distributed two-dimensional-like micrometer-sized grooves prepared on thermally oxidized Si wafer with photo lithography techniques. The interface geometry is measured by high-speed video camera for the Capillary number (=μU/γ, μ:viscosity, U:average contact line speed, γ:surface tension) ranged 0.5 ~ 3.5×10^-5. The contact line shows stick-slip motion resulting in the induction of surface wave near the contact line which decays within the length from the contact line of ~0.1L where L=(γb²/2πρU²)^1/3. The dissipation of this wave should enhance the dynamic contact angle.