Three-dimensional thermal-conductivity-tensor measurement of a polymer crystal by photothermal probe-beam deflection

Using Fourier transforms we have calculated the solutions of the three-dimensional (3D) thermal-conduction equation in an anisotropic medium. The temperature distribution at the surface of the sample and a 3D thermal-conductivity tensor is measured by the photothermal-probe-beam-deflection technique. We show that the expression for the deflection angle can be the same as in an isotropic medium, provided that an effective thermal conductivity relative to the polymeric-chain axis and a rescaled sample thickness are considered. This theoretical model is found to be in good agreement with the experimental data for an orthorhombic polydiacetylene sample (4BCMU).