Dynamic contact angle in rim instability of dewetting holes

The effects of dynamic contact angle (theta(d)), between a substrate and the melt of a dewetting polymer thin film, on the evolution of rim instabilities of dewetting holes were reported. Various theta(d)'s were achieved by covering SiOx surfaces with different coverage of octadecyltrichlorosilane. On each surface, the morphology of the dewetting holes was examined in detail as the hole grew to a certain size. Rim instabilities, in terms of undulations in both r and z directions, became more pronounced as theta(d) increased, under which condition, narrower and higher rims were also observed. Experimentally, atomic force microscopic scans of the rim were used to obtain the rim profile, which was predicted using theta(d). The predicted rim profile was used, in combination with the analysis of Rayleigh instability of a cylindrical fluid, to interpret the rim instability. The model captures the basic trend of the rim instability dependency on theta(d). The study demonstrates the importance of the substrate properties on the rim instability and the destabilization of polymer thin films during hole growth. (c) 2006 American Institute of Physics.