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 (Ntb) liquid crystal phase of odd numbered flexible dimer molecules. It is found that the Ntb phase is strongly shear-thinning. At shear stresses below 1 Pa the apparent viscosity of Ntb is 1000 times larger than in the nematic phase. At stress above 10 Pa the Ntb 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.