Photopyroelectric calorimetry of liquids; recent development and applications

This paper is a synthesis of the main photopyroelectric (PPE) calorimetric techniques proposed in the last years for accurate measurements of dynamic thermal parameters of liquids. The area of interest is restricted to liquids because, due to the perfect sample-sensor thermal contact, accurate quantitative results can be obtained and consequently, intimate processes occurring in liquids (as molecular associations, structural changes in nanofluids, adulteration and spoilage of liquid foodstuffs, etc.) can be studied. The paper describes the possibilities offered by the two main used PPE detection configurations, “back” and “front”in investigating two dynamic thermal parameters: thermal diffusivity and effusivity. In the paper we analyzed only the information contained in the phase of the PPE signal, due to the fact that the phase, as a source of information, leads to more accurate results than the amplitude. A study of the accuracy of the investigations when using the chopping frequency, or sample’s thickness as scanning parameters is also made. Some basic applications concerning high-resolution measurements of thermal diffusivity and effusivity of some “special”liquid samples (magnetic nanofluids, adulterated vegetable oils) are described. A new possibility of using the thickness scan of the phase of the PPE signal of a liquid, in order to obtain the thermal parameters of a solid is analyzed.