Photopyroelectric method for determination of thermophysical parameters and detection of phase transitions in fatty acids and triglycerides. Part I: Principles, theory, and instrumentational concepts

Abstract

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. JAOCS 72, 273-279 (1995).

Photopyroelectric observation of melting in valeric (C5 : 0), linoleic (C18 : 2), linolenic (C18 : 3) and tricosanoic (C23 : 0) free fatty acids

“…The PPE cell is a cold-Ðnger-based system, allowing the operation both below and above the ambient (Dadarlat et al 1995a). The typical temperature variation rate was 0É35 K min~1 with acquisitions at each 0É05 K. The pyroelectric sensor was a 0É3 mm thick single LiTaO 3 crystal.…”

“…The sample accommodated the all available The PPE cell geometry used to accommodate the sample. space between the sensor and an opaque calibrated cell (0É57 mm thick) (Fig 1b) (Bicanic et al 1995 ;Dadarlat et al 1995a). The sample was introduced in the cell always in a liquid form and Ðlled the space between the sensor and an opaque metallic layer due to capillarity.…”

Thermal characterization of ZnBeMnSe mixed compounds by means of photopyroelectric and lock-in thermography methods

“…The thermal diffusivity can be obtained with various methods [9][10][11][12]. In this paper, the thermal diffusivity of the investigated materials is obtained with PPE technique [13][14][15] in the back detection configuration, coupled with the chopping frequency of the incident radiation scanning procedure. In order to validate the results obtained by PPE calorimetry, lock-in thermography technique is used for determining the thermal diffusivity of the crystals.…”

Metrological Aspects of Auto-normalized Front Photopyroelectric Method to Measure Thermal Effusivity in Liquids

“…The heating produces an electric current that carries information on the thermal diffusivity (α) and thermal effusivity (e) of the sample [5,6].…”