Simulations of solid-on-solid models of spreading of viscous droplets

We have studied the dynamics of spreading of viscous non-volatile fluids on surfaces by Monte Carlo simulations of solid-on-solid (SOS) models. We have concentrated on the complete wetting regime, with surface diffusion barriers neglected for simplicity. First, we have performed simulations for the standard SOS model. Formation of a single precursor layer, and a density profile with a spherical cap shaped center surrounded by Gaussian tails can be reproduced with this model. Dynamical layering, however, only occurs with a very strongly attractive van der Waals type of substrate potential. To more realistically describe the spreading of viscous liquid droplets, we introduce a modified SOS model. In the new model, tendency for dynamical layering and the effect of the surface potential are in part embedded into the dynamics of the model. This allows a relatively simple description of the spreading under different conditions, with a temperature like parameter which strongly influences the droplet morphologies. Both rounded droplet shapes and dynamical layering can easily be reproduced with the model. Furthermore, the precursor width increases proportional to the square root of time, in accordance with experimental observations.