Differential thermal lens temperature scanning approach to glass transition analysis in polymers: application to polycarbonate

In this paper, mode mismatched thermal lens spectrometry is applied to determine the thermal and optical properties of polycarbonate as a function of temperature. The focus of the experiments was in the temperature range between 120 deg C and 170 deg C, where the sample glass transitions occurs. In order to validate and evaluate the sensitivity of the proposed method we have also carried out conventional differential scanning calorimetry measurements. The results showed that the temperature dependence of the signal amplitude of the thermal lens provided a better definition in locating the glass transition compared to the differential scanning calorimetry data. In addition, a sharp decrease in the thermal diffusivity values at the beginning of the sample glass transition was observed. According to the Debye model, this change was attributed to the variation of the sample elastic constant throughout the glass transition. Finally, we propose this procedure, called the differential thermal lens temperature scanning approach, as a new method for the investigation of phase transitions in transparent polymers.