COMPETITION BETWEEN DEWETTING AND CRYSTALLIZATION IN THIN POLYMER FILMS
Brian Okerberg, Brian Berry, Timothy Garvey, Jack Douglas, Alamgir Karim, and Christopher Soles
We investigate the competition between dewetting and crystallization fronts in thin polymer films where the velocities of these fronts are modulated by varying the temperature from a low temperature regime, where crystallization dominates, to a high temperature regime, where dewetting is more rapid. Specifically, thin films of poly(caprolactone) (PCL) on n-octyldimethylchlorosilane (ODS) treated substrates are investigated as a model system exhibiting this general phenomenon. Pattern formation at low temperatures is dominated by spherulitic structures at random positions throughout the film, but at higher temperatures we find that spherulitic growth can induce dewetting at the grain boundaries between the spherulites (crystallization-induced dewetting) (CID). We provide evidence that CID arises from the high stresses at the grain boundaries that accompany the volume change upon crystallization. The CID is found to be concentrated in regimes where the angles between the grains are larger than a critical angle and this effect allows for considerable control over the resulting film morphology.
Name: Brian Okerberg
Mentor: Christopher Soles
Room/Building/Stop: B230, 224, 8541
T: 301-975-5230, F: 301-975-3918