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 dete rmine the thermal and optical properties of polycarbonate as a function of temperature. The focus of the experiments was in the temperature range betw een 120 degreesC and 170 degreesC, where the sample glass transitions occur s. In order to validate and evaluate the sensitivity of the proposed method we have also carried out conventional differential scanning calorimetry me asurements. The results showed that the temperature dependence of the signa l amplitude of the thermal lens provided a better definition in locating th e glass transition compared to the differential scanning calorimetry data. In addition, a sharp decrease in the thermal diffusivity values at the begi nning of the sample glass transition was observed. According to the Debye m odel, this change was attributed to the variation of the sample elastic con stant throughout the glass transition. Finally, we propose this procedure, called the differential thermal lens temperature scanning approach, as a ne w method for the investigation of phase transitions in transparent polymers .