Instability and pattern formation in thin liquid films on chemically heterogeneous substrates.

The surface instability, dynamics, morphology, and spontaneous dewetting of a thin liquid film on chemically heterogeneous substrates are studied on t he basis of 3D nonlinear simulations. A new mechanism of dewetting in the p resence of heterogeneity is proposed where the instability is engendered by the gradient of intermolecular interactions that lead to a microscale wett ability contrast. The time scale of instability, which can be several order s smaller than the spinodal dewetting time scale on homogeneous surfaces, v aries inversely with the potential difference induced by the heterogeneity. Heterogeneity can even destabilize spinodally stable films, reduce the tim e of rupture substantially for thicker films, and decrease the dependence o f rupture time on the film thickness. The presence of heterogeneity produce s complex and locally ordered morphological features that are not predicted by the spinodal dewetting, for example "ripples" and "castle-moat" structu res, radially symmetric structures, and a lack of undulations before the bi rth of a hole. The precise morphological pattern selection depends on the s ize of the heterogeneity, the potential difference caused by the heterogene ity, the film thickness, and also the spinodal characteristics of the subst rate: The resulting morphologies can be understood on the basis of simple a rguments that consider interplay among these factors.