Rupturing of polymer films with rubbing-induced surface defects

It has been a long-standing question whether dewetting of polymer film from non-wettable substrate surfaces wherein the bicontinuous morphology never forms in the dewetting film is due to spinodal instability or heterogeneous nucleation. In this experiment, we use a simple method to make the distinction through introduction of topographical defects of the films by rubbing the sample surface with a rayon cloth. Spinodal dewetting; is identified for those films that dewet by a characteristic wavevector, q{*}, independent of the density of rubbing-induced defects. Heterogeneous nucleation, on the other hand, is identified for those with q{*} increasing with increasing density of defects. Our result shows that PS films on oxide coated silicon with thickness less than approximate to 13 nm are dominated by spinodal dewetting, but the thicker films are dominated by nucleation dewetting. We also confirm that spinodal dewetting does not necessarily lead to a bicontinuous morphology in the dewetting film, contrary to the classic theory of Cahn