Orientational order and dynamics of molecules in the nematic phase 4-trans-(4-trans-n-propylcyclohexyl)cyclohexanenitrile

Abstract

A sample of 4-trans-(4-trans-n-propylcyclohexyl)cyclohexanenitrile (CCH3) has been synthesized containing six deuterons randomly distributed between axial and equatorial positions in the cyanylated ring. The local orientational order parameters for axes fixed in this ring have been measured by obtaining the deuterium N.M.R. spectrum. The results show that the lack of symmetry and flexibility of the molecule affect the order matrix. The biaxiality in the local order matrix is small and could be close to zero, depending on the location, as yet unknown, of the principal axes. The spectral densities J₁(ω) and J₂(ω) have been measured for a sample oriented with the director orthogonal to B₀. It is shown that these spectral densities cannot be explained by the mechanism of relaxation being caused solely by director fluctuations. It is also not possible to explain the spectral densities by invoking only small-step rotational diffusion. A combination of these two relaxation mechanisms does fit the data.