Anomalous capillary flow of a molten metal – Ageing contact angle

An anomalous behavior of dynamic contact angle and position of contact line has been recently observed in capillary flow experiments of molten alloys. The experimental setup consists of a combination of a wetting/non-wetting solid substrate with the molten alloy attracted by the wetting wall and simultaneously repelled by the non-wetting substrate. The dynamic receding contact angle experiences a non-monotonic evolution towards its equilibrium value, i.e, it drops below the equilibrium and then it overshoots. The receding contact line moves either gradually or abruptly, in different experiments.

We postulate a novel diffusive boundary condition for the phase field model where the quasi-equilibrium contact angle changes in time, as a result of slow chemical changes at interfaces, which affect interface energies and therefore – the quasi-equilibrium contact angle. We discover two distinct topological paths: one is characterized by a coalescence of liquid-solid contact domains, the other by a contact line separation. The selection of the two paths in the configurational space depends on both contact ageing parameters and viscosity of the melt.