Raman scattering study of orientation order parameters in thermotropic biaxial nematic LC

There has been considerable interest in the liquid crystalline phases formed by bent-core molecules, since these molecules were considered to have a biaxial nematic phase. In an effort to understand the orientation behavior and the degree of phase biaxiality in bent-core mesogen, Raman spectroscopy has been used to measure the scattering intensities for orthogonal linear polarization. This straightforward methodology allows the values of both uniaxial, $<$P$_{200}>$ and $<$P$_{400}>$, and biaxial order parameters, $<$P$_{220}>$, $<$P$_{420}>$, and $<$P$_{440}>$ to be quantified. From experimentally derived order parameters, the most probable orientation distribution functions are constructed. The results of these measurements will be presented in the context of experimental evidence of phase biaxiality obtained by other methods including X-ray diffraction and NMR