Use of photoacoustic effect for the detection of phase transitions in liquid crystal mixtures

We report on a laser induced photoacoustic study of the nematic-to-isotropi c transition in certain commercial nematic liquid crystal mixtures, namely BL001, BL002, BL032 and BL035. A simple analysis of the experimental data u sing the Rosencwaig-Gersho theory shows that the heat capacities of all the se compounds exhibit a sharp peak as the temperature of the sample is varie d across the transition region. Also, substantial differences in the photoa coustic signal amplitudes in nematic and isotropic phases have been noticed for all the mixtures. The increased light scattering property of the nemat ic phase may be the reason for the enhanced photoacoustic signal amplitude in this phase.