Correlation between structural and dynamic mechanical transitions of regenerated silk fibroin

Dynamic mechanical analysis (DMA) was applied to investigate the correlation between dynamic mechanical behaviors of regenerated silk fibroin (RSF) and its structural transition which was characterized by near-infrared (NIR) spectroscopy. The tan δ peak split of DMA demonstrated that the apparent glass transition of amorphous RSF film (at around 177 °C) was the contribution of both uncrystallizable and crystallizable segments through homogeneous amide–amide hydrogen bonds, which were gradually separated from each other and produced disordered and β-sheet domains during ethanol treatment. Furthermore, DMA was also applied as “thermal fingerprint” to investigate water effect on the disordered domains of silk fibroin. The results showed that glass transition temperature of permanently disordered domains in crystallized RSF films was increased from 155 °C to 190 °C after thermal dehydration, and even approached 205 °C for stretched RSF films.