SIMPLE AND ACCURATE AC CALORIMETER FOR LIQUID-CRYSTALS AND SOLID SAMPLES

We have designed, built and calibrated a microcomputer-controller automated a.c. calorimeter for liquid crystals and solid samples, in the temperature range from 30 to 250-degrees-C, in which we enhance several features of previous ones reported in the literature. We have incorporate the lock-in amplifier model 5302 from EG&G in our set-up, which permits to extend the frequency range to 1 mHz. This allows the performance of suitable frequency sweeps in order to choose the optimum operating frequency for low thermal conductivity materials. The calorimeter has been calibrated with the 8OCB liquid crystal compound. The resolution obtained for C(p) values was better than 0.1% and the absolute error around 5%. As applications, we show the ferroelectric transition of the triglicerine sulphate (TGS), the Nematic-Smetic A transition of the 8OCB and a study in a binary system of ferroelectric liquid crystals, SCE9-SCE10.