Molecular dynamics study of thin film instability and nanostructure formation

The instability dynamics of a thin liquid film at nanoscale on a substrate, which is confined by an upper wall at a distance, is studied by the molecular dynamics (MD) simulation. Two sources of instability are investigated in the context of nanostructure generation: (1) substrate heating; (2) electric field. In the case of instability induced by substrate heating, the temperature gradient in the film layer reaches up to 2.5 K per nanometer. A substantial amount of growth is observed at this temperature gradient for the waves with lower wave numbers. The thermocapillarity effect seems to be the major source of the instability. The electric field is imposed on the liquid film by considering the upper wall as an electrode. Three cases of different types of electrodes and interactions are compared on the instability characteristics. The electric field acts as a strong source of destabilization and consistently leads to the formation of structures bridging the substrate and the upper wall. In addition, present MD results are compared with those by the continuum theory, which shows a significant deviation from the present data in the prediction of the formation time.