Eur. Phys. J. E (2010) 31: 145-152
https://doi.org/10.1140/epje/i2010-10556-8

Regular Article

Orientational order in liquid crystals exhibited by some binary mixtures of rod-like and bent-core molecules

Raman Research Institute, C.V. Raman Avenue, 560 080, Bangalore, India

^* e-mail: pratibha@rri.res.in
^** e-mail: nvmadhu@rri.res.in

Received: 26 June 2009
Revised: 3 December 2009
Published online: 1 March 2010

Abstract

We report measurements of the temperature variations of the optical birefringence in the nematic (N) and partial bilayer SmA (SmA_d) phases in 4-n-octyloxy 4^′ -cyanobiphenyl made of rod-like (R) molecules and five mixtures of this compound with 1,3-phenylene bis[4-(3-methylbenzoyloxy)] 4^′ -n- dodecylbiphenyl 4^′ -carboxylate, made of bent-core (BC) molecules. The birefringence decreases with the concentration x of the BC molecules but the macroscopic order parameter initially decreases upto 11mol% of BC molecules and subsequently increases with x . This is attributed to the possible formation of polar clusters of BC molecules. Orientation of BC molecules changes between the N and SmA_d phases and the birefringence data in the two phases imply that the kink angle of the BC molecules is ∼ 90^° rather than ∼ 110^° as obtained from calculations which minimize the energy of the molecule. IR spectroscopic measurements on the mixture with 11mol% of BC molecules have been used to estimate the molecular order parameter S of the R molecules, and to provide additional support for a relatively small kink angle of BC molecules.