Unusual odd-even effects depending on the monomer chain length in nematic liquid crystals made of rod-like dimersBrindaban Kundu1, Santanu Kumar Pal1, 2, Sandeep Kumar1, R. Pratibha1 and N. V. Madhusudana1
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
received 31 October 2008; accepted in final form 17 January 2009; published February 2009
published online 13 February 2009
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.
64.70.M- - Transitions in liquid crystals.
61.30.Gd - Orientational order of liquid crystals; electric and magnetic field effects on order.
77.84.Nh - Liquids, emulsions, and suspensions; liquid crystals.
© EPLA 2009