Reactive wetting of Hg–Ag system at room temperature

We study the spreading characteristics of a reactive-wetting system of mercury (Hg) droplets on silver (Ag) films at room temperature. Using a recently developed method for reconstructing the dynamical three-dimensional shape of spreading droplets from a microscope top-view, we study the time evolution of the droplet radius and its contact angle. We find that the process consists of two stages: (i) the “bulk propagation” regime, controlled by chemical reaction on the surface, and (ii) the “fast flow” regime which occurs within the metal film as well as on the surface, and consists of both linear (in time) and diffusive propagation. The transition time between the two main time regimes depends solely on the thickness of the Ag film. A final reaction band with an intermetallic compound Ag4Hg3 is formed in this process. We review our results for the kinetic roughening characteristics of the top-viewed mercury–silver triple line, which is the statistical characterization of the morphology of the triple line, expressed in terms of the growth and roughness scaling exponents. The latter are used to determine the universality class of the system.