Eur. Phys. J. E (2019) 42: 138
https://doi.org/10.1140/epje/i2019-11902-0

Regular Article

Measurement of visco-elastic properties in a binary system of hockey stick-shaped and calamitic mesogens

¹ Department of Physics, University of North Bengal, 734 013, Siliguri, India
² Martin-Luther-Universität Halle-Wittenberg, Institut für Chemie, Physikalische Chemie, Halle, Germany

^* e-mail: mkdnbu@yahoo.com

Received: 18 May 2019
Accepted: 8 October 2019
Published online: 28 October 2019

Abstract

Temperature variation of the splay elastic modulus (K₁₁) and rotational viscosity () have been measured throughout the entire nematic (N phase of a binary liquid crystal system comprising of host calamitic compound, 4^′-octyloxy-4-cyanobiphenyl (8OCB) and small amount of a hockey stick-shaped mesogen, 4-(3-decyloxyphenyliminomethyl) phenyl 4-decyloxycinnamate (SF7). Two different structural conformations play a significant role in the phase behavior leading to a noticeable shrinkage in the nematic width. During cooling in the nematic phase, both K₁₁ and enhance monotonically and divulge an evidence of pretransitional fluctuation near the Smectic-A (Sm-A) transition. With increase in the dopant concentration, the slope of the temperature-dependent K₁₁ and becomes uniformly steeper. The observed variations are explained in accordance with the formation of smectic-like clusters in the nematic phase. A representative model of the smectic-like clusters in the nematic phase is presented. However, the obtained values of have found to be between that of conventional calamitics and typical bent-core mesogens. Measurement of the temperature-dependent orientational order parameter (〈P ₂〉 ) and activation energy (E_a) has also been carried out for all the studied mixtures, exhibiting a small augmentation due to the addition of a hockey stick-shaped compound. This indicates an enhancement in intermolecular packing within the mixtures which further influences the molecular motions.