Dewetting of thin polystyrene films absorbed on epoxy coated substrates

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Various characteristics of dewetting of thin polystyrene (PS) films absorbed on highly cross-linked epoxy-coated and silicon oxide covered substrates are studied as a function of PS film thickness (20<h<1300 A) by optical microscopy, atomic force microscopy, and x-ray and neutron reflectivity. For a silicon oxide covered substrate, the nucleation of holes and growth (NG) mechanism is observed for h>h(c1) whereas the spinodal dewetting (SD) occurs through the growth of surface undulations for h<h(c1), where h(c1) is approximately 4R(g). For an epoxy-coated substrate, the NG mechanism is observed for h>h(c2) while the SD mechanism is observed for h<h(c2), where h(c2) is approximately 6R(g). We demonstrate that the highly cross-linked epoxy-coated silicon substrate leads to retardation of the PS film dewetting in comparison to the silicon oxide covered silicon substrate. Moreover, we confirm that the epoxy-coated substrate leads to a significant decrease in the fraction of dewetted area at the apparent equilibrium stage of dewetting due to the anchoring effect of PS molecules caused from the cross-linked networks of the epoxy layer. In contrast the retardation effect of the epoxy-coated substrate on the rate of dewetting is more remarkable for relatively thinner PS films (h< approximately 800 A) than thicker films ( approximately 800<h<1300 A) since the short-range intermolecular interactions are dominant for relatively thin PS films. Thus the highly cross-linked epoxy-coated substrate has a large influence on the kinetics, morphology, and mechanism of dewetting of thin PS films.