Development of Heat Capacity Spectroscopy and Application to Relaxation Process in Amorphous Materials

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The frequency dependence of the heat capacity is expected to be observed near the glass transition temperature of a supercooled material. However, the maximum measurable frequency in conventional ac calorimetry is ultimately limited by the thermal divvusivity and the size of sample. The purpose of this research is to develop a new technique that makes it possible to obtain the frequency-dependent heat capacities over a wide range of frequency between 1 Hz and 100 kHz.A cryostat working in a temperature region from liquid helium temperature up to ablut 100゜c and a high-precision system for temperature control have been constructed. The electrical circuits using a lock-in amplifier have been also constructed for heat capacity measurements on the basis of ac method. The calorimetry system has been automated by using a microcomputer. A thin metal resistor element for the use as heater/thermometer has been devised by vapor deposition(Ni, Au) and rf sputtering(Au, Pt). It has been found that the measurement system can be simplified by combining the two elements with the same temperature coefficient of resistance. A thin wire method has been also developed. The performance of the system has been tested by doing experiments on the blass transition of glycerol. The materials of liquid crystals have been also studied. Thermodynamic properties of pentylcyanobiphenyl and the related compounds (replacing the benzene ring by cyclohexane ring) have been studied by DTA, heat capacity measurements and Raman spectroscopy. The relaxation mechanisms have been discussed about the blass transition phenomena of the mixtures.