Splay and bend elastic constants in the nematic phase of some disulfide bridged dimeric compounds.

We report measurements of the temperature dependences of the splay (K11) and bend (K33) elastic constants of several homologues and a binary mixture of disulfide bridged symmetric dimers made of alkoxy cyanobiphenyl monomeric units. All of them have an even number m of carbon and sulfur atoms in the linking chain and expected to have linear conformations. Both K(11) and K(33) alternate depending on the parity of x which is the number of carbon atoms in the alkyl chain of a monomer. We will refer to this as 'odd-even' effect. This effect, occurs near the nematic-isotropic transition temperature. T(NI), but monotonically decrease with m at lower temperatures. We argue that these results imply large rotational fluctuations of the two halves of the dimers about the S-S bond giving rise to average bent conformations near T(NI). At lower temperatures those conformations which can adapt better to the given curvature deformation in the medium are favored.