Quantitative photoacoustic depth profilometry of magnetic field-induced thermal diffusivity inhomogeneity in the liquid crystal octylcyanobiphenyl

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Abstract
An observed change in the photoacoustic signal frequency response upon the application of a transverse magnetic field across octylcyanobiphenyl samples in the nematic phase at 37 °C and 37.5 °C is reported. The application of a recent thermal-wave theory developed for depth profiling of continuously inhomogeneous condensed phases has given quantitative profiles of thermal diffusivity decreases extending to 20–30 μm below the liquid crystal surface. These decaying depth profiles are qualitatively consistent with earlier photoacoustic temperature scans of liquid crystals and are a measure of the extent of bulk reorientational effects due to the magnetic field, as well as the extent of the influence of the surface as a domain reorientation inhibitor in the kG range.