Dynamics and morphology of holes in dewetting of thin films

Abstract

The formation and growth of holes in apolar nonslipping Newtonian thin films subjected to long-range Lifshitz-van der Waals forces are investigated based directly on numerical solutions of the thin-film equation. The nonphysical divergences of the hydrodynamic model and of the van der Waals force at the three-phase contact line are removed by inclusion of the short-range Born repulsion. Three distinct regimes of the hole growth after its appearance are identified: (1) a short, unsteady phase in which the dynamic contact angle and velocity change rapidly, followed by (2) a long, quasi-steady phase with slow logarithmic changes, and finally (3) a hindered phase in which rims of the neighboring holes overlap and lead to formation of equilibrium drops. The cross section of the rim surrounding a growing hole is noncircular and asymmetric, with higher slopes near the contact line. A slight depression is created ahead of the moving rim, but the regions of the film away from the rim remain undisturbed. For very viscous (e.g., polymeric) liquids displaying small contact angles, a nonlinear regime of hole growth (radius ˜ time^q, with the exponent q≈ 0.7-0.9) is obtained for realistic time scales.