Influence of thermal and optical properties on the visibility of liquid-crystal phase transitions in photoacoustic spectroscopy

The thermal, optical light absorption and light scattering properties of a liquid crystal can be distinguished and separately studied by a single technique, pulsed photoacoustic spectroscopy (PPAS), by using different excitation/detection configurations. The advantages of performing complementary thermal and optical measurements without modifying the sample environment are demonstrated in the case of a typical liquid crystal: 4-octyl-4'-cyanobiphenyl (8CB). Results show that light scattering can strongly influence the PPAS response signal through the light absorption profile, especially al:phase transitions subjected to small changes in thermal properties, such as the Nematic/isotrope phase transition. (C) 1998 American Institute of Physics.