Ultrasound-order director fluctuations interaction in nematic liquid crystals: A nuclear magnetic resonance relaxometry study

F. BONETTO; E. ANOARDO; R. KIMMICH

JOURNAL OF CHEMICAL PHYSICS

American Institute of Physics (AIP)

Lugar: Melville, New York, USA; Año: 2003 vol. 118 p. 9037 - 9043

0021-9606

Field-cycling nuclear magnetic resonance (NMR) relaxometry was used to study the spin-lattice relaxation dispersion of selected standard nematic liquid crystals at different temperatures, in presence and absence of a monochromatic ultrasonic field. It was found that sonication changes the relaxation dispersion and, in some cases, it shortens the spin-lattice relaxation time on a broad frequency range. The theoretical interpretation is based on the interaction between the ultrasound and the nematic director field. A model previously developed and tested in preliminary experiments, is now successfuly applied in a broader temperature range for different compounds. We found a remarkably good agreement with earlier experiments in pentylcyanobiphenyl (5CB). Nonetheless, new interesting features and stronger effects were observed in p-azoxyanysole (PAA). The analysis of our results clearly suggests a sound-induced enhancement of order director modes.