PHOTOPYROELECTRIC DETERMINATION OF THERMOPHYSICAL PARAMETERS AND DETECTION OF PHASE-TRANSITIONS IN FATTY-ACIDS AND TRIGLYCERIDES .2. TEMPERATURE-DEPENDENCE OF THERMOPHYSICAL PARAMETERS

The photopyroelectric (PPE) technique was used to detect solid-to-liquid phase transitions in saturated [C6:0, C10:0, C12:0, C16:0 palmitic acid (P), C18:0 stearic acid (S)] and unsaturated (C18:2) fatty acids and some triglycerides (PSP, PPS). By using the standard PPE configuration with a thermally thin and optically opaque sample and a thermally thick sensor (a1.1); the temperature behavior of the volume-specific heat in a temperature range that includes the melting points for C10:0, C12:0, C16:0, and C18:0 was obtained. When the standard PPE configuration, with sample and sensor both being thermally thick and the sample being optically opaque (a1.2), was used, the information contained in the phase of the PPE signal allowed direct measurement of the thermal diffusivity for C10:0, C12:0, and PSP. The inverse configuration with a thermally thick sample and thermally thin sensor (b1.2) or a semitransparent thermally thick sensor (b2) was used to obtain critical behavior of the thermal effusivity for C10:0 and C12:0, respectively. Critical behavior of the thermal conductivity for same samples was computed from information obtained from amplitude and phase measurements (a1.2), or by combining a1.1 and b1.2 data. The history (age, storage conditions, annealing) of the samples affects the critical behavior of thermal parameters.