Simultaneous measurement of light transmission and heat flow in a modified differential scanning calorimeter

A commercial DSC cell has been modified to allow simultaneous measurement of heat flow and light transmission. A special fiber optic probe capable of transmitting and receiving light is located immediately above the sample. The sample is held in a reflective aluminum pan during the measurement. Maximum optical signal intensity is recorded when the sample becomes completely transparent. The light from the probe will pass through the sample, reflect off the bottom of the pan, and then pass up through the sample again and back into the probe. The method was developed to augment the normal DSC heat-flow measurement. We find that the additional optical information is useful in elucidating the nature of thermal transitions in polymeric materials. Any transition, physical or chemical, that is accompanied by an appreciable change in optical transmission can be studied by this technique. The probe is useful even in investigations where only the optical signal is desired, because one can make use of the temperature programming and data aquisition capabilities of the DSC instrument. The presence of the probe tip near the sample does not seriously degrade the heat-flow signal. Good calorimetric accuracy is maintained, albeit some baseline curvature is introduced. Several applications of the technique are described. These include melting and crystallization of polymers, solubility behavior of polymer–polymer and polymer–additive blends, and sintering of polymer particles during oxidative degradation.