Role of substrate commensurability on non-reactive wetting kinetics of liquid metals

The dynamics of spreading of liquid metal atoms via molecular dynamics is considered vs. the commensurability of the solid surface with respect to the size of the liquid atoms. The solid surfaces are modeled as rigid (1 0 0) oriented Ni and, for two series of simulations, the lattice spacing of the substrate is varied from the regular equilibrium spacing to a commensurate situation with Au or Ag drops spreading spontaneously on top. The diffusion is calculated in the layered region of the liquid in contact with the two different solid surfaces and then compared. Then, the dynamic evolution of the contact angle is fitted to Molecular Kinetic Theory and compared with the two substrate geometries. It is observed that the friction parameter scales as the inverse of the diffusion in the interfacial region. The change in ordering induced by the commensurate substrate is characterized by examining the density profiles across the solid/liquid interface and fitting the curve by an exponential decay with a characteristic correlation distance 1/kappa. It is shown that the commensurability/non-commensurability of the solid surface with respect to the liquid atoms changes the ordering, which plays a significant role in the dynamics, a feature not properly taken into account in the present formulation of Molecular Kinetic Theory. (C) 2009 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.