Unusual odd-even effects depending on the monomer chain length in nematic liquid crystals made of rod-like dimers

¹  Raman Research Institute - C.V. Raman Avenue, Bangalore 560 080, India
²  Department of Chemical and Biological Engineering, University of Wisconsin-Madison Madison, WI 53706, USA

Corresponding author: nvmadhu@rri.res.in

Received: 31 October 2008
Accepted: 17 January 2009

Abstract

We report physical studies on the nematic phase exhibited by five members of a homologous series of symmetric dimers which have cyanobiphenyl end groups and, a disulphide bridging group in the spacer. All of them have rod-like conformations in the nematic phase, but unusually, the nematic-isotropic transition temperature, the birefringence and the dielectric anisotropy exhibit “odd-even” effects depending on the number of carbon atoms in the alkyl chain of a monomeric moiety. Further, the lowest “even” homologue exhibits a nematic-nematic transition. We argue that these phenomena arise from the relatively facile rotational fluctuations of the two monomeric moieties around the central S–S bond, whose orientation with respect to the long molecular axis changes between the “even” and “odd” members.