Motion and arrest of a molten contact line on a cold surface: An experimental study

An experimental study is presented of the behavior of a molten contact line under conditions which simulate what happens when a molten droplet touches a subcooled solid, spreads partly over it, and freezes. We restrict our attention to the case where the solid and melt are of the same material and have approximately the same thermal properties, and reach two conclusions. First, we show that an advancing molten contact line is arrested at an apparent dynamic contact angle, which for a given material depends primarily on the Stefan number based on the temperature difference between the fusion point and the temperature of the solid over which the melt spreads. Second, during much of the spreading prior to contact-line arrest, the relationship between the melt’s apparent dynamic contact angle and the contact-line speed appears to obey the Hoffman–Tanner–Voinov law with the equilibrium contact angle taken as zero.