Twist-bend nematic drops as colloidal particles: Structural features

K. S. Krishnamurthy, D. S. Shankar Rao, Santosh Y. Khatavi, and Channabasaveshwar V. Yelamaggad
Phys. Rev. E 107, 034706 – Published 28 March 2023
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Abstract

The mesogen CB7CB [1″,7″-bis(4-cyanobiphenyl-4′-yl)heptane], mixed with a small quantity of a long chain amphiphile, is examined for the structural features of twist-bend nematic (NTB) drops acting as colloidal inclusions in the isotropic and nematic environments. In the isotropic phase, the drops nucleating in the radial (splay) geometry develop toward escaped radial, off-centered structures, involving both splay and bend distortions. With further growth, they transform into low-birefringence (near-homeotropic) objects, within which remarkably well-organized networks of parabolic focal conic defects evolve in time. In electrically reoriented near-homeotropic NTB drops, the pseudolayers develop an undulatory boundary possibly attributable to saddle-splay elasticity. In the matrix of the planar nematic phase, NTB droplets appearing as radial hedgehogs attain stability in the dipolar geometry, through their association with hyperbolic hedgehogs. With growth, on transformation of the hyperbolic defect into its topologically equivalent Saturn ring around the NTB drop, the geometry turns quadrupolar. Significantly, dipoles are stable in smaller drops, while quadrupoles are stable in larger ones. The dipole-quadrupole transformation is reversible, but is hysteretic with respect to drop size. Importantly, this transformation is often mediated by nucleation of two loop disclinations, one appearing at a marginally lower temperature than the other. The existence of a metastable state with partial formation of a Saturn ring and persistence of the hyperbolic hedgehog raises a question relating to the conservation of topological charge. In twisted nematics, this state features in the formation of a giant unknot that binds all NTB drops together.

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  • Received 9 January 2023
  • Accepted 14 March 2023

DOI:https://doi.org/10.1103/PhysRevE.107.034706

©2023 American Physical Society

Physics Subject Headings (PhySH)

Polymers & Soft Matter

Authors & Affiliations

K. S. Krishnamurthy*, D. S. Shankar Rao, Santosh Y. Khatavi, and Channabasaveshwar V. Yelamaggad

  • Centre for Nano and Soft Matter Sciences, Survey No. 7, Shivanapura, Bangalore 562162, India

  • *murthyksk@gmail.com

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Vol. 107, Iss. 3 — March 2023

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