Molecular-Dynamics Simulation of Sliding Drops

We use large-scale molecular dynamics (MD) to model drops of liquid sliding across a solid surface under the influence of an external force. The simulations enable us to extract the local, microscopic dynamic contact angle and the velocity of the contact-line normal to itself at all points around the drop. Consistent with macroscopic observations, our results confirm that the dynamic contact angle is a function of the local contact-line velocity in the normal direction , where is the velocity of the drop’s center of mass and is the slope of the contact line with respect to the direction of travel. We model the velocity-dependence of the microscopic contact angle using the molecular-kinetic theory, and if slip between the first layer of liquid molecules and the solid surface is accounted for, the contact-line frictions recovered are identical with those found in previous MD studies of spreading drops. Moreover, despite the relatively small scale of the simulations, flow within the drop with respect to the solid surface is consistent with that observed in macroscopic experiments.