Photopyroelectric calorimetry of solids

An alternative photopyroelectric (PPE) technique that combines the front detection configuration (FPPE) with the thermal wave resonator cavity (TWRC) method is proposed. The theoretical analysis of the FPPE signal indicates that the configuration also offers information about both fluid sample and backing solid material. It is demonstrated that the normalized phase of the FPPE signal has an oscillating dependence as a function of the sample's thickness. In the thermally thin regime for the sensor and liquid sample, the method can be used for direct measurement of backing thermal effusivity. This article presents experimental results on solid materials, with various values of thermal effusivity (Cu, brass, steel, glass, bakelite, and wood), used as backings in the detection cell. A study of the sensitivity of the technique for different liquid/backing effusivity ratios is performed. The main result of this article is the possibility of deriving the thermal effusivity of a solid sample (backing material) by monitoring the thickness of a fluid with well-known properties. In such a way, the so-called coupling fluid is not anymore a disturbing factor; however, its properties can be used to obtain the value of the thermal effusivity of a solid. The method proved to be suitable especially for thermal effusivity investigations of low thermal conductors. An application on polymer composites with different liquid/powder content is presented.