Self-Assembled Orientation of Polymer Chains in Methylcellulose Gel during Drying Process

By the study of drying process of methylcellulose aqueous solution, the behavior of the polymer chains in physical gel became clear.Methylcellulose powder was dissolved in water and kept at an adequate condition to be in physical gel state during the drying process. Morphological time change of a cap-shaped gel droplet on a glass plate was observed by polarized optical microscope (POM) and wide angle X-ray scattering (WAXS) apparatus during and after the drying process until the droplet was completely dried up to be a solidified thin film. By POM observation, the whole image of the thin film showed just as a single negative spherulite crystallite, and the film measured by WAXS showed that its ac plain is parallel to the substrate plane on the assumption that the methylcellulose crystal structure is same as trimethylcellulose.This suggests that polymer chains in the methylcellulose gel rearranged nearly on concentric circles around the center of the sample. This alignment suggests that the motion of polymer chains is occurred along the periphery of the gel droplet in the drying process and a self-assembled orientation of the polymer chains limited by the periphery is induced to reduce the total free energy in the solidified thin film.