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Thermotropic, Side-chain Ordered Polymeric Coatings: Gas Permeability Switching via a Thermal Stimulus
Co-Author: Sergei Nazarenko
UV curing provides a rapid and energy efficient means of preparing thin films and coatings easily applied over large areas. This work aims to explore the feasibility of a thermally stimulated optical switch or permeation switch via rapid UV curing using highly ordered structures. Solvent free UV-cured, C8F17 perfluorinated acrylate network was developed that show a unique side chain order. Similarly, an amorphous C6F13 perfluorinated acrylate thin film with comparable chemical structure was prepared as a control. Well defined order is a result of the rigid rod structure of the longer perfluorinated side chain, confirmed using WAXD. DSC indicates that there is a very high content of ordered structure in C8F17 films at ambient conditions where the amorphous C6F13 film remains rubbery. C8F17 side chain order is disrupted through a sharp thermotropic transition, giving rise to increased larger hole sizes and free volume concentrations probed via positron annihilation and pressure, volume, temperature dilatometry. Transport properties agree with free volume analysis as transport of small gasses shows a dramatic increase in permeability, caused by an increase in diffusivity through the thermotropic transition.