Critical Thickness in Dewetting Films

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We study dewetting of thin polymer films with built-in topographical fluctuations produced by rubbing the film surface with a rayon cloth. By varying the density of imposed surface defects, we unambiguously distinguish spinodal dewetting, which dominates in liquid films thinner than a characteristic thickness = 13.3 nm, from heterogeneous nucleation in the thicker films. Invariance of this characteristic thickness upon more than a decade change in the defect density makes kinetic effect an unseemly origin. A crossover of the spinodal line provides a consistent picture. This interpretation, however, contends the current understanding of molecular interactions in apolar liquid films.