LAUSR

Temperature dependences of thermal, thermogravimetric, and acoustic properties were investigated for the crystalline silk fibroin films crystallized by methanol exposure. The crystallization peak in the thermal flow at ~ 225 ◦ C, which was prominent in the amorphous silk film, disappeared in the crystalline silk film. The heat-treatment at ~ 100 ◦ C for 1 h reduced the weight by ~5.5% due to the release of water molecules. The formation of beta-sheets in the film did not have any substantial effect on the acoustic properties of the longitudinal acoustic mode in the crystalline film. However, the heat treatment of the methanol-exposed silk film induced clear anomalies in the acoustic mode behaviors in a specific temperature range between −20 ~ 30 ◦ C. The existence of water molecules has more profound effect than the crystallinity does on the acoustic properties of silk fibroin films.