Search for: All records

We study theoretically and numerically chirality and saddle-splay elastic constant (K_24) enabled stability of multiple-twist-like nematic liquid crystal (LC) structures in cylindrical confinement. We focus on the so-called radially-z-twisted (RZT) and radially-twisted (RT) configurations, which simultaneously exhibit twists in different spatial directions. We express free energies of the structures in terms of dimensionless wave vectors, which characterise the structures and play the role of order parameters. The impact of different confinement anchoring conditions is explored. A simple Landau-type analysis provides insight into how different model parameters influence the stability of structures. We determine conditions for which the structures are stable in chiral and also nonchiral LCs. In particular, we find that the RZT structure could exhibit macroscopic chirality inversion on varying the relevant parameters. This phenomenon could be exploited for measurements of K_24. 

We studied numerically external stimuli enforced annihilation of a pair of daughter nematic topological defect (TD) assemblies bearing a relatively strong topological charge |m|=3/2. A Landau- de Gennes phenomenological approach in terms of tensor nematic order parameter was used in an effectively two-dimensional Cartesian coordinate system, where spatial variations along the z-axis were neglected. A pair of {m=3/2,m=−3/2} was enforced by an appropriate surface anchoring field, mimicking an experimental sample realization using the atomic force microscope (AFM) scribing method. Furthermore, defects were confined within a rectangular boundary that imposes strong tangential anchoring. This setup enabled complex and counter-intuitive annihilation processes on varying relevant parameters. We present two qualitatively different annihilation paths, where we either gradually reduced the relative surface anchoring field importance or increased an external in-plane spatially homogeneous electric field E. The creation and depinning of additional defect pairs {12,−12} mediated the annihilation in such a geometry. Furthermore, we illustrate the absorption of TDs by sharp edges of the confining boundary, accompanied by m=±1/4↔∓1/4 winding reversal of edge singularities, and also E-driven zero-dimensional to one-dimensional defect core transformation.