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Thermotropic biaxial nematic order parameters and phase transitions deduced by Raman scattering
Southern, C D; Brimicombe, P D; Siemianowski, S D; Jaradat, S; Roberts, N; Gortz, V; Goodby, J W; Gleeson, H F
Epl. 2008;82(5):6.
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Abstract
Raman Scattering was used to investigate biaxiality in the nematic phase formed by the bent-core material, C5-Ph-ODBP-Ph-OC12. Linearly polarised light was normally incident on a homogeneously aligned sample, and the depolarisation ratio was measured over a 360 degrees rotation of the incident polarisation for the Raman-active phenyl stretching mode. By modeling the bent-core structure and fitting to the depolarisation data, both the uniaxial ([P-200] and [P-400]) and biaxial ([P-220], [P-420] and [P-440]) order parameters, are deduced. We show unequivocally the presence of a uniaxial to biaxial nematic phase transition approximately 30 degrees C above the underlying smectic phase. Further, we report the temperature evolution of the biaxial and uniaxial order parameters, which increase in magnitude continuously with reducing temperature, reaching values of 0.1, -0.15 and -0.18 for [P-220], [P-420] and [P-440], respectively. Copyright (c) EPLA, 2008.
Keyword(s)
LIQUID-CRYSTALS; MESOGENS; MOLECULES; ORIENTATIONAL ORDER; SYMMETRY
Bibliographic metadata
- Southern, C. D. Brimicombe, P. D. Siemianowski, S. D. Jaradat, S. Roberts, N. Gortz, V. Goodby, J. W. Gleeson, H. F. 30 EDP SCIENCES S A LES ULIS CEDEX A 307EP