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 s ingle technique, pulsed photoacoustic spectroscopy (PPAS), by using di fferent excitation/detection configurations. The advantages of perform ing complementary thermal and optical measurements without modifying t he sample environment are demonstrated in the case of a typical liquid crystal: 4-octyl-4'-cyanobiphenyl (8CB). Results show that light scat tering can strongly influence the PPAS response signal through the lig ht absorption profile, especially al:phase transitions subjected to sm all changes in thermal properties, such as the Nematic/isotrope phase transition. (C) 1998 American Institute of Physics.