Universal Nature of the Nematic Phase

Similarities and differences between molecular order in the nematic and twist-bend nematic phases of a symmetric liquid crystal dimer

“…This approximate way of measuring the molecular orientational order has the advantage that it can be obtained from experimental values of any second-rank property of the liquid crystal sample, and has been measured for a large number of nematic liquid crystals in each case over the whole range of temperature of the liquid crystal phase. Most temperature profiles of S have been found to have a very similar shape, as reported by Simo ˜es et al, 14 so that S(T) is regarded as being a characteristic property of a N U phase. Thus, Haller 32 has suggested that the temperature dependence S for a nematogen should follow the equation:…”

“…The temperature dependence of the molecular orientational order parameter, S, for ''classical'' nematic phases composed of rodlike molecules has a characteristic form, which is that of a continuously increasing value throughout the whole range of the phase. 14 The compound studied here, DTC5C9, whose structure is shown in Fig. 1, has two nematic phases, N U and N TB and unlike almost all other materials reported so far has a negative dielectric anisotropy.…”

“…The molecules KS7 molecules are similar to those included by Simo ˜es et al 14 in their comparison of the temperature profiles of the order parameter in being a reasonable approximation to a rigid cylindrical shape, with the assumed symmetry axis, defining the direction of the single order parameter, S(KS7), describing the orientational order of the molecules. A local order parameter, S zz (KS7) is defined for the para axis of the difluoroterphenyl group, for which it is reasonable to assume axial symmetry about z, and to also to assume that the cylinder axis makes a fixed angle, y s , with z.…”