Second-order elasticity of liquid crystals within their nematic state at high frequencies

Autor:	C. Schorr, C. Grammes, Jörg Baller, R. Jiménez, Jürgen Schreiber, C. Fischer, Jan-Kristian Krüger, D. Rogez, K.-P. Bohn, Patrick Alnot
Rok vydání:	1995
Předmět:	Brillouin Spectroscopy Materials science Condensed matter physics Biaxial nematic business.industry Instability MBBA Brillouin zone chemistry.chemical_compound Optics chemistry Liquid crystal Elasticity (economics) business Anisotropy
Zdroj:	Physical Review E. 51:2115-2128
ISSN:	1095-3787 1063-651X
DOI:	10.1103/physreve.51.2115
Popis:	Within this work we present Brillouin and ultrasonic investigations performed on the liquid crystals p-methoxybenzylidene p-(n-butylaniline) (MBBA), p-azoxyanisol (PAA), 4-cyano-4-n-alkylbiphenyles (nCB), and 4-n-pentoxybenzylidene-4'-n-octoaniline (5O.8). Special attention has been paid to the evolution of a significant splitting of the two longitudinal polarized acoustic modes within the nematic phase. Angle-resolving Brillouin spectroscopy allowed the determination of the complete stiffness tensors and hence a discussion of the propagation of quasitransverse polarized acoustic modes in the nematic state of liquid crystals. We analyze the behavior of the eigenvectors of the relevant acoustic modes and discuss their significance for the propagation of quasishear modes. For 5O.8 we report an acoustic instability within its nematic state. We confirm the existence of a universal thermal relaxation mechanism of weak activation energy for the nematic state of classical liquid crystals. The observed hypersonic anisotropy is discussed in terms of that relaxation mechanism and is compared with that of glass-forming liquid crystals.
Databáze:	OpenAIRE
Externí odkaz:	https://explore.openaire.eu/search/publication?articleId=doi_dedup___::2bcc6ae283c2a12632fc5cad318b1072 https://doi.org/10.1103/physreve.51.2115 Zobrazit plný text záznamu