Study of the interfacial structure in epoxy bilayer films using neutron reflection

Dewetting of thin polystyrene films absorbed on epoxy coated substrates

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.