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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Authors

  • Seyyed Muhammad Salili

    Chemical Physics Interdisciplinary Program and Liquid Crystal Institute, Kent State University, Kent, OH 44242, USA, Chemical Physics Interdisciplinary Program and Liquid Crystal Institute, Kent State University, Kent, OH 44242 USA

  • Chanjoong Kim

    Chemical Physics Interdisciplinary Program and Liquid Crystal Institute, Kent State University, Kent, OH 44242, USA

  • Samuel Sprunt

    Department of Physics, Kent State University, Department of Physics, Kent State University, Kent, OH 44242, USA

  • James Gleeson

    Department of Physics, Kent State University, Department of Physics, Kent State University, Kent, OH 44242, USA

  • Owain Parri

    Merck Chemicals Ltd., Chilworth Technical Centre, University Parkway, Southampton SO16 7QD, UK

  • Antal J\'akli

    Chemical Physics Interdisciplinary Program and Liquid Crystal Institute, Kent State University, Chemical Physics Interdisciplinary Program and Liquid Crystal Institute, Kent State University, Kent, OH 44242, USA, Liquid Crystal Institute, Liquid Crystal Institute, Kent State University, Chemical Physics Interdisciplinary Program and Liquid Crystal Institute, Kent State University, Kent, OH 44242 USA