Centre for Nano and Soft Matter Sciences, Survey No. 7, Shivanapura, Bangalore 562162, India.
Phys Rev E. 2023 Mar;107(3-1):034706. doi: 10.1103/PhysRevE.107.034706.
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 (N_{TB}) 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 N_{TB} drops, the pseudolayers develop an undulatory boundary possibly attributable to saddle-splay elasticity. In the matrix of the planar nematic phase, N_{TB} 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 N_{TB} 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 N_{TB} drops together.
介晶 CB7CB [1″,7″-双(4-氰基联苯-4′-基)庚烷]，与少量长链两亲物混合，用于研究作为各向同性和向列相环境中的胶体包含物的扭曲向列（N_{TB}）液滴的结构特征。在各向同性相中，沿径（展）向几何形状成核的液滴向逃逸的径向外中心结构发展，涉及展向和弯曲变形。随着进一步生长，它们转变成低双折射（近各向同性）物体，在其中时间上会演化出组织良好的抛物焦锥缺陷网络。在电重取向的近各向同性 N_{TB}液滴中，伪层产生波动边界，可能归因于马鞍-展弹性。在平面向列相的基质中，呈径向外刺状的 N_{TB}液滴以偶极几何形状通过与双曲外刺状的关联而在 dipolar 几何形状中获得稳定性。随着生长，双曲缺陷转变成其拓扑等效的土星环围绕 N_{TB}液滴时，几何形状变为四极。重要的是，偶极在较小液滴中稳定，而四极在较大液滴中稳定。偶极-四极转变是可逆的，但与液滴尺寸有关存在滞后现象。重要的是，这种转变通常由两个环形电四极子的核化介导，其中一个出现在比另一个稍低的温度下。存在部分形成土星环和保持双曲外刺状的亚稳态，引发了与拓扑电荷守恒相关的问题。在扭曲向列相中，这种状态以形成束缚所有 N_{TB}液滴在一起的巨型纽结为特征。
