(Top Left) Brillouin shift measurements of the SMP polymer versus temperature over the glass transition. The Tg is readily identified at 21.91 °C by a substantial discontinuity in the slope of the temperature-Brillouin curve. (Bottom Left) Validation of our technique by measuring the freezing temperature of water molecules which have permeated the polymer. As expected, a sharp slope is observed at T ∼ 0 °C. (Right) A comparison of DMA-derived Tg (by parameter) along with the transition as measured using DSC and Brillouin spectroscopy. The Brillouin-derived Tg agrees best with DSC and the most commonly used DMA parameter () with less agreement among less common parameters. Heating and cooling are shown for DMA measurements to show hysteresis. Because SMPs are activated by heating in a medical context, Brillouin shift measurements were taken during heating only.
