PHOTOPYROELECTRIC METHOD FOR DETERMINATION OF THERMOPHYSICAL PARAMETERS AND DETECTION OF PHASE-TRANSITIONS IN FATTY-ACIDS AND TRIGLYCERIDES .1. PRINCIPLES, THEORY, AND INSTRUMENTATIONAL CONCEPTS

The photopyroelectric (PPE) technique is proposed to detect solid-to-liquid phase transitions in fatty acids and triglycerides. Various PPE configurations and cell geometries were used to obtain thermal parameters in the vicinity of the melting points for these samples. In the standard (SPPE) configuration used to determine specific heat, the sample is thermally thin and optically opaque, while the sensor itself is thermally thick. The same configuration, but with a thermally thick sample instead, allows direct measurement of the sample's thermal diffusivity. The temperature dependence of the thermal effusivity was obtained for a thermally thick sample and a thermally thin sensor [inverse (IPPE) configuration], and for a semitransparent thermally thick sensor by making use of the front configuration.