In this paper we discuss the use of an alternative photothermal technique for measurements of thermal properties of liquids. The proposed technique is based upon the concept of thermal wave interferometry. The liquid sample is confined between two thin pyroelectric detectors. One of these detectors acts as a modulated absorber of light while the other is used for sensing the temperature fluctuations transmitted through the liquid layer. The good agreement between the values of the thermal properties we got with the present technique and those reported in the literature demonstrates the capability of the technique for full characterization of the thermal properties of liquids.

A gas sensing device based on a thermal wave resonator cavity is outlined. It is experimentally tested by monitoring the presence of several hydrocarbon vapors in air via the measurement of the thermal diffusivity. It is also shown that its time-dependent response may be used to follow the vapor diffusion. It is shown that its characteristic response time is linearly correlated to the thermal diffusivity value of the mixture. The steps toward the development of a practical sensing device are further discussed.

A double-purpose open photoacoustic cell, suitable for optical and thermal characterization of liquid samples is described. An experimental method for the determination of very low concentrations of contaminants in liquid substances is proposed. The proposed technique was used to determine the concentration of Chromium (VI) in water via the measurement of its optical absorption coefficient. To test the suitability of the proposed technique for experimental determination of thermal properties of liquids, studies on ethanol were performed. The agreement between experimentally obtained thermal properties and values reported in the literature is good.

In this paper, we describe a new, simple, and fast photothermal method for detecting the presence of adulterants in commercial gasolines. The method consists essentially of measuring the time evolution of the gasoline vapor in an originarily air-filled closed cell using a pyroelectric sensor. The transient photothermal signal amplitude data fitting yields two parameters, namely, a saturation signal amplitude and the characteristic time for approaching saturation. From the values, two figures of merit are defined. The method was tested with a universe of 210 commercial samples collected in different gas stations. It is shown that the proposed method has an uncertainty of 5.7%. This good accuracy, together with its simplicity and fast response, may render it useful for developing a portable device for fast checking in field analysis.