Thermotropic biaxial nematic order parameters and phase transitions deduced by Raman scattering

TY - JOUR

T1 - Thermotropic biaxial nematic order parameters and phase transitions deduced by Raman scattering

AU - Southern, C. D.

AU - Brimicombe, P. D.

AU - Siemianowski, S. D.

AU - Jaradat, S.

AU - Roberts, N.

AU - Gortz, V.

AU - Goodby, J. W.

AU - Gleeson, H. F.

PY - 2008/6/1

Y1 - 2008/6/1

N2 - 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.

AB - 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.

KW - LIQUID-CRYSTALS

KW - ORIENTATIONAL ORDER

KW - MOLECULES

KW - SYMMETRY

KW - MESOGENS

UR - http://www.scopus.com/inward/record.url?scp=79051471232&partnerID=8YFLogxK

U2 - 10.1209/0295-5075/82/56001

DO - 10.1209/0295-5075/82/56001

M3 - Article

SN - 0295-5075

VL - 82

SP - 1

EP - 7

JO - Europhysics Letters

JF - Europhysics Letters

IS - 5

M1 - 56001

ER -