Thermophysical Properties of Polymer Thin Films Measured on Ionic Liquid
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The intrinsic thermophysical properties of amorphous and semicrystalline polymer thin films are characterized on the surface of ionic liquid to minimize the substrate effect. The coefficients of thermal expansion (CTE) of amorphous polystyrene (PS) and semicrystalline poly(3-hexylthiophene) (P3HT) are measured to determine the glass transition temperature (Tg) and melting temperature (Tm) for PS and P3HT, respectively. The Tg of PS thin film decreases when the film thickness (h) is smaller than 6 times of polymer radius of gyration (Rg), regardless of the polymer molecular weight. For P3HT thin films, the deviation of Tm from the bulk P3HT increases with increasing molecular weight because of the reduced crystallite size. This study provides a facile strategy to measure the intrinsic thermophysical properties of polymer thin films under minimized substrated effect.