Flow properties of a twist-bend nematic liquid crystal

Abstract

We present the first shear alignment studies and rheological measurements in the twist-bend nematic (N_tb) liquid crystal phase of odd numbered flexible dimer molecules. It is found that the N_tb phase is strongly shear-thinning. At shear stresses below 1 Pa the apparent viscosity of N_tb is 1000 times larger than in the nematic phase. At stress above 10 Pa the N_tb viscosity drops by two orders of magnitude and the material exhibits Newtonian fluid behavior. This is consistent with the heliconic axis becoming normal to the shear plane via shear-induced alignment. From measurements of the dynamic modulus we estimate the compression modulus of the pseudo-layers to be B ∼ 2 kPa; this value is discussed within the context of a simple theoretical model based upon a coarse-grained elastic free energy.