Detection of Phase Biaxiality in Liquid Crystals by Use of the Quadrupole Shift in Xe 131 NMR Spectra

An experimental method to unambiguously distinguish between uniaxial and biaxial liquid crystal phases is introduced. The method is based on the second order quadrupole shift (SOQS) observable in Xe-131 NMR spectra of xenon dissolved in liquid crystals. It is shown that besides revealing the biaxiality, the Xe-131 SOQS offers a novel method to determine the tilt angle in smectic C phases. As an example, the Xe-131 SOQS in a ferroelectric liquid crystal is reported. It yields up a biaxial phase in between isotropic and smectic C phases.