Crystallization of Poly(ethylene oxide) on Topographically Patterned Substrates
Brian C. Okerberg, Christopher Soles, Jack F. Douglas, Alamgir Karim
Crystallization of poly(ethylene oxide) (PEO) on topographically patterned substrates is investigated. Primary nucleation was dramatically enhanced during solvent drying on patterned substrates compared to flat films. The nucleation density also increased sharply with decreasing film thickness. In contrast, there was no change in nucleation density for recrystallized films under similar conditions, indicating that the drying process was responsible for this change. Examination of the spherulite nucleus in recrystallized films on patterned substrates revealed that the lamellae comprising the sheaf structure grow with an edge-on orientation, even in relatively thin films. These edge-on lamellae maintained their orientation over large lateral distances, despite the fact that flat-on lamellae were observed over the majority of the film.In addition to the preferred tilting of the sheaf structure at the early stages of spherulitic growth, the sheaf was also found to align along the direction of the substrate channels. The degree of alignment increased with decreasing film thickness and decreasing channel pitch. Lamellar branching was enhanced when the growth direction was at a small angle to the channel direction. These results highlight the influence of the crystallization geometry and confinement on lamellar branching and the development of the spherulitic morphology.