Pattern-directed to isotropic dewetting transition in polymer films on micropatterned surfaces with differential surface energy contrast
D Julthongpiput, Wenhua Zhang, Jack F. Douglas, Alamgir Karim, Michael J. Fasolka
Surface chemical patterns can both cause and direct dewetting in overlying thin films. However, a key factor in this behavior, the magnitude of surface energy differences between pattern domains ( ?g ), is largely unevaluated. To probe the effect of this variable on film dewetting, we employ micropatterned substrates that exhibit a continuous, calibrated, gradient in ?g. ???Using polystyrene (PS) as a demonstration case, we apply these combinatorial surfaces to measure the morphology and kinetics of film dewetting as ?g diminishes. Our analysis illuminates transitions in PS dewetting and critical ?g ?values associated with these regimes. For ?g > 14 mJ/m2 ordered droplet arrays are formed, while for ?g < 7 mJ/m2, isotropic dewetting occurs. A competition between these limiting behaviors is exhibited where 7 < ?g < 14 mJ/m2. Successfully demonstrated for this particular system, our combinatorial approach is promising for examining a wide range of film and surface phenomena.