PATTERN-FORMATION IN SPONTANEOUS DEWETTING OF THIN APOLAR FILMS

Various stages of evolution of surface instability leading to dewettin g are investigated for thin (<100 nm) fluid films subjected to the lon g range van der Waals interactions on a nonwettable solid. The problem s of pattern selection and complete three-dimensional morphology are r esolved based on numerical solutions of the nonlinear two-dimensional thin film equation. The initial small scale random nonhomogeneities ar e quickly reorganized into a large scale coherent bicontinuous structu re consisting of ''hills'' and ''valleys,'' which is reminiscent of th e classical picture of the spinodal decomposition in the linear approx imation. On the level of a ''unit-cell,'' the bicontinuous structure s lowly evolves into an increasingly axisymmetric circular pattern, and eventually a growing circular hole (dry spot) is formed. Scaling argum ents, as cell as the simulations give the characteristic mean area of a unit-cell containing a single hole to be proportional to (h(0)(4) ga mma/\S\), where h(0) is mean thickness, gamma is surface tension, and S is the spreading coefficient. (C) 1997 Academic Press.