Self-organization in unstable thin liquid films: dynamics and patterns in systems displaying a secondary minimum

Abstract

Dynamics, stability, morphology, and dewetting of a thin film (<100 nm) under the influence of a long-range van der Waals attraction combined with a short-range repulsion are studied based on numerical solutions of the nonlinear two-dimensional (2-D) thin film equation. Area and connectivity measures are used to analyze the morphology and the distinct pathways of evolution of the surface instability. The initial disturbance resolves into an undulating structure of uneven 'hills and valleys'. Thereafter, the morphology depends on the mean film thickness relative to the minimum of the force curve. Relatively thin films to the left of the minimum transform directly into an array of droplets via the fragmentation of ridges. At long times, the droplets merge due to ripening. In contrast, relatively thick films are dewetted by the formation and growth of isolated, circular holes. Coalescence of holes eventually leads to the formation of ridges and drops. Films of intermediate thickness display a rich combination of different morphologies. Thus, the morphology and the sequence of evolution depend crucially on the form of the potential and the film thickness relative to the location of the minimum in the force vs. thickness curve. Different types of patterns can, therefore, even co-exist on a heterogeneous surface.