The Determination of the Heat Capacities of Liquids with Time Resolved Thermal Lens Calorimetry: A More Accurate Procedure

Abstract

The application of thermal lens calorimetry to the determination of the heat capacities of liquids has been reported in the literature. The accuracy is poor; a 60% error was reported for the heat capacity of methanol. This article describes a modified procedure that dramatically improves the accuracy of the method. A set of standard solutions was prepared from solvents of known heat capacity and the dye indophenol blue. The concentration of the dye in each solvent was adjusted to produce a solution with the same absorbance at 632nm, the wavelength of the laser used to perform the studies. These standards were used to produce a calibration line that allows one to systematically adjust the lens to sample distance and the size of the aperture in the diaphragm through which the laser beam passes. These adjustments are based upon the size of the thermal bloom produced as the laser beam passes through a sample. Standards were prepared from acetone, benzene, carbon tetrachloride, ethanol and methanol at three different absorbances. The calibration lines were used to determine the heat capacities of chloroform and toluene at each absorbance. The average relative errors for the heat capacities of chloroform and toluene were 3.0% and 2.6%, respectively.

Surface Tension Gradients Induced by Temperature: The Thermal Marangoni Effect

“…More recently, a laser-induced Marangoni effect has been used as a tool for studying the properties of crude oil and oil͞water emulsions (14) and the behavior of surfactant molecules at the gas-liquid interface in the presence of convection currents (15). In such studies, the interaction between the laser beam and the surface of the absorbing liquid increases temperature via a photothermal effect (16). Again, a surface tension gradient develops and the motion of the liquid is made visible by adding small particles (such as talc) on its surface.…”

Study of the thermal diffusivity in low-response optical systems combining a thermal lensing approach with a standard addition method

“…[3,4,5,6] The thermal lensing effect consists of the variation of the local refractive index by inducing a temperature gradient in a non-linear medium using a light laser beam. [7] This gradient can induce a change in the local refractive index of the medium, thereby generating a 'lens', which in turn, affects the propagation of the pumping or any other light traversing it. [7,8] The intensity of the Gaussian laser passing through a suspension of nanoparticles has a radial distribution around the optical axis.…”

“…[7] This gradient can induce a change in the local refractive index of the medium, thereby generating a 'lens', which in turn, affects the propagation of the pumping or any other light traversing it. [7,8] The intensity of the Gaussian laser passing through a suspension of nanoparticles has a radial distribution around the optical axis. [8] This distribution can be described by equation 1.…”

Steady-state and transient thermal lens behavior in the dual beam Z-scan arrangement

“…The thermal lens effect, first demonstrated by Gordon et al [1] has since then become an important tool for chemistry in trace level analytical determinations [2], for calorimetry [3,4] and by measuring of low absorbances [5]. Basically the thermal lens evolves as a result of optical absorption and heating of the sample in region exposed to the incident radiation.…”