Wetting behaviour on a solid surface contaminated with a liquid layer

摘要

We consider the wetting dynamics of an (axisymmetric) drop of a liquid 1 deposited on a solid substrate covered by a thin layer of a liquid 2 ― a contaminant, or maybe an agent to aid wetting. Diffusion of liquid 2 into liquid 1 by an (assumed) Fickian mechanism leads to a variable (increasing), effective solid/drop interfacial free energy, concomitant with spreading, and thus modifying behaviour. Spreading is accelerated, but more interesting is the approach to near equilibrium conditions. The triple line "overshoots" and then recedes. By considering a simplified, two-dimensional drop which is given a slight push to one side after deposition, we establish a regime of spontaneous translational drop motion due to different capillary equilibria pertaining at the two triple lines. Diffusional wetting is compared with reactive wetting.