Orientational order of a spin probe dissolved in nematic liquid crystals. An electron resonance investigation

Abstract

The electron resonance spectra of a nitroxide spin probe, dissolved in the mesophases of several nematogens, have been measured as a function of the angle between the director and the magnetic field. The orientational order parameter, text-decoration:overline P ₂, of the probe was then determined from the line separations while the novel higher order parameter, text-decoration:overline P ₄, was extracted from the linewidths. The values of text-decoration:overline P ₂ and text-decoration:overline P ₄ measured for the spin probe are found to be in good agreement with a simple molecular field theory of nematic liquid crystals. This agreement contrasts with marked discrepancy between the simple theory and the results of Raman light scattering experiments to determine the analogous order parameters.