Reactive wetting of metal-metal systems involves numerous physicochemical phenomena that occur on a myriad of time scales. Kinetic roughening is a comparatively late-time phenomenon, marked by a transition from a circularly symmetric contact line to an irregular or roughened contact line. Roughening is typically characterized by the Family-Vicsek relation, in which the contact-line width, defined as the second moment of the fluctuations in the contact-line, scales initially as tb, but subsequent to saturation as La, where L is a variable length segment of the contact-line. The growth exponent, b, characterizes the dynamics of the roughening process, whereas the roughness exponent a characterizes the morphology of the saturated contact-line at long times. On the basis of these two exponents one can associate the kinetic-roughening process within a certain universality class. Applying this method reveals information about the underlying mechanisms that generate the roughening phenomena. We will also introduce an additional statistical tool that provides more detailed information about the roughening process, the persistence probability, P(t), that points along the contact line will never cross some reference level within a certain time. P(t) decays as a power law, P(t)~t-q, where q is the persistence exponent.
We repeat previous Au-Hg experiments, but this time conduct wetting in an inert (N2) atmosphere on temperature-controlled substrates. These features minimize oxidation effects on the Hg/gas interface and permit the assessment of the possible effects of reaction compound on the roughening: above 122 0C, a transition of reaction compound from Au2Hg to Au3Hg occurs. By varying the temperature over a given stable range of the respective compounds, we assess the effects of reaction kinetics on the roughening. In addition, we calculate the persistence probability for the first time in this system, and study its dependence on temperature. We study the effects of substrate thickness by performing these experiments over a range of Au layer thicknesses from 0.2mm to 1mm.
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