We have studied the dynamics of spreading of viscous non-volatile fluids on
surfaces by MC simulations of 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 (DL), 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 DL 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 DL can easily be reproduced with the model. Furthermore, the
precursor width increases proportional to the square root of time, in
accordance with experimental observations. PACS: 68.10.Gw, 05.70.Ln, 61.20.Ja.Comment: to appear in Physica A (1994), standard LaTex, 20 page