Rheology of a Twist-bend Nematic Liquid Crystal
ORAL
Abstract
First detailed flow shear alignment studies and rheological measurements in the twist-bend nematic ($N_{tb} )$ liquid crystalline phase of odd numbered flexible dimer molecules is presented. It is found that the $N_{tb} $ phase is strongly shear-thinning. At shear stresses below $1Pa$ the apparent viscosity of the $N_{tb} $ phase is $1000$ times larger than in the nematic phase. At stresses above $10Pa$ the $N_{tb} $ viscosity drops by two orders of magnitude and the material exhibits Newtonian fluid behavior. The results are consistent with the behavior of a system with pseudo-layer structure with layer spacing determined by the heliconical pitch. From the measurements of dynamic modulus we estimate the compression modulus of the pseudo-layers to be $B\sim 2kPa$; this value is discussed within the context of a simple theoretical model based upon a coarse-grained elastic free energy.
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