Volume 82, Number 5, June 2008
|Number of page(s)||6|
|Section||Condensed Matter: Structural, Mechanical and Thermal Properties|
|Published online||26 May 2008|
Thermotropic biaxial nematic order parameters and phase transitions deduced by Raman scattering
School of Physics and Astronomy, The University of Manchester - Manchester, M13 9PL, UK, EU
2 Department of Chemistry, The University of York, Heslington - York, YO10 5DD, UK, EU
Corresponding author: firstname.lastname@example.org
Accepted: 17 April 2008
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° 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 ( P200 and P400 ) and biaxial ( P220 , P420 and P440 ) order parameters, are deduced. We show unequivocally the presence of a uniaxial to biaxial nematic phase transition approximately 30°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 P220 , P420 and P440 , respectively.
PACS: 61.30.-v – Liquid crystals / 61.30.Gd – Orientational order of liquid crystals; electric and magnetic field effects on order / 78.30.-j – Infrared and Raman spectra
© EPLA, 2008
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