Thermal Diffusivity of Linear Alkanes and its Behaviour with the Size of the Chain: Study with a Photopyroelectric Technique

Thermal transport properties of substances are fundamental for science and engineering. Among these properties, thermal diffusivity characterizes the way materials transport heat under nonstationary conditions. The manner in which this thermal property behaves with the size or molecular configuration is very important to understand the mechanisms involved in heat transport. It is a complicated work to study variations on this thermal property taking these two variables (size and configuration) together. Linear alkanes have essentially the same spatial configuration, varying only the molecular size (the number of involved carbon atoms in the molecule), so they are ideal substances to study the behaviour of thermal properties with the molecular size alone. In this work photopyroelectric technique, taking the sample´s thickness as variable (the so-called TWRC method), is used for thermal diffusivity measurements of linear alkanes, from 1-heptane to 1-heptadecane. It is shown that this thermal property increases with the molecular size. This behaviour can be explained in a very simple way if it is considered that the increase in molecular size increases “routes” of heat transport.

Heat transport in epoxy and polyester carbonyl iron microcomposites: The effect of concentration and temperature

Temperature dependence of the thermal diffusivity in composites of epoxy and polyester resins, loaded with carbonyl iron particles, has been studied using the photopyroelectric technique. Increments of eight and 2.5 times the thermal conductivity of the polymers are obtained, as the volume concentration of microparticles is increased from 0% to 40% for epoxy and from 0% to 20% for polyester matrices, respectively. Additionally, the thermal diffusivity falls systematically as the temperature is increased from 270 to 400 K; the effect is more pronounced for high concentration of microparticles in epoxy composites. The glass transition of the composites is explored by implementing a numerical differentiation algorithm. In order to explain the consequences of the loading of the composites on the thermal conductivity, a modified Lewis-Nielsen model, which includes the presence of crowded regions in the samples, is used to study heat transfer in a wide range of particle concentrations.