We report measurements of the temperature dependences of the splay $\left(K_{11}\right)$ and bend $\left(K_{33}\right)$ elastic constants of several homologues and a binary mixutre 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. $T_{\text{NI}}$, 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 $T_{\text{NI}}$. At lower temperatures those conformations which can adapt better to the given curvature deformation in the medium are favored.

• Received 24 February 2010

DOI:https://doi.org/10.1103/PhysRevE.82.061703