Crystallization of Poly(ethylene oxide) in Nanoimprinted Channels
Brian Okerberg, Christopher Soles, Jack Douglas, Hyun Wook Ro, Alamgir Karim
Polymers Division, National Institute of Standards and Technology, 100 Bureau Drive,
Gaithersburg, Maryland 20899-8541
The crystallization behavior of poly(ethylene oxide) (PEO) films patterned by nanoimprint lithography is studied. The imprinted PEO film consists of parallel lines, approximately 240 nm wide and 350 nm tall, on a 400 nm pitch with a residual layer of approximately 10 nm. A spherulitic superstructure, typically observed for bulk PEO samples, is observed by optical microscopy. This result indicates that the crystal lamellae communicate through the continuous thin residual layer into the discrete patterned regions that span hundreds of micrometers. In the discrete imprinted lines, the lamellae generally have a flat-on orientation with respect to the substrate. When the radial growth direction of the spherulite is parallel to the lines, a terraced morphology develops where the lamellae grow largely unperturbed along the imprinted line direction. When the radial growth direction is orthogonal to the lines, the lamellae are also elongated along the imprint line direction, suggesting that the crystal growth direction within the lines is orthogonal to the spherulite growth direction. The mold walls do not significantly influence the orientation of the lamellae indicating that the orientation is determined in the early stages of crystallization.