Geometrical anisotropy dependence of thermal diffusivity in lyotropic nematics: Mode mismatched thermal lens measurements

In this work the quantitative theoretical treatment for two beam mode mismatched thermal lens spectrometry is applied to investigate the thermal diffusivity anisotropy of two lyotropic mixtures: (1) potassium laurate, decanol and water and (2) potassium laurate, potassium chloride and water in the nematic calamitic phase. The ratio between the thermal diffusivities parallel and perpendicular to the director has been shown to be smaller than those reported for thermotropic liquid crystal. This observation is explained by using a simple model where this ratio is correlated to the micellar shape anisotropy.