Knotting and linking of nematic disclination lines in chiral nematic colloids is an important binding mechanism that could be used for the assembly of soft matter photonic circuits. Disclination lines in chiral nematic liquid crystals exhibit rich entangled structures in systems with dispersed colloidal inclusions. Numerous metastable and stable states separated by low energy barriers allow for simple rewiring of the braids. We have introduced a new visualization scheme where variations in splay, bend and twist deformations are followed separately. This allows us to display the effect of chirality on the director profile of the disclinations, and to uncover the mechanism of their rewiring. We demonstrate the richness of structures by performing a survey of all possible disclination structures that entangle a pair of homeotropic silica microspheres in a pi-twisted cholesteric cell using numerical free-energy minimization and laser tweezers assisted microscopy.
COBISS.SI-ID: 2452068
Chiral cholesteric microdroplets self-assemble into photonic structure that is the foundation of a new generation of microlasers. Understanding their structure and self-organization is therefore of prime importance for liquid crystal-based photonics. In this article, the frustration of chiral ordering is explored in cholesteric liquid crystal droplets with planar degenerate anchoring using numerical modeling. Droplets of variable pitches are studied, demonstrating the role of a gradually increasing cholesteric pitch and the corresponding equilibrium structures. All previously known structures are identified and the structures presented with director fields are complemented with a detailed description of the defect regions. The characteristic halfdiameter +2 disclination is found to be in fact a double-helix of two lambda +1 disclination lines, whereas the full-diameter +1 disclination is composed of an alternating series of tau 1/2 and lambda +1/2 disclination rings. Finally, two new meta-stable cholesteric structures -Lyre and Yeti- are found, which are characterised by complex compositions of cholesteric disclinations. Understanding the structure and topology of cholesteric microdroplets is important for our understanding of the properties of 3D microlasers.
COBISS.SI-ID: 2508388
Optical, elastic and rheological properties of liquid crystals are important material parameters for the design and assembly of soft matter photonic microcircuits, which predetermine the strength and stability of topological entanglement, as well as the resonant transfer of light between individual liquid crystal photonic elements, such as an optical fibre and an optical resonator. To this aim we have performed an extensive study of temperature variations of physical parameters in ambient-temperature nematic liquid crystal mixtures of bent-core (BC) and rodlike molecules (5CB): birefringence Δn; static dielectric constants ; splay K11 and bend K33 elastic constants; and rotational viscosity γ1. Both Δn and εII decreases rapidly with increasing BC concentration, whereas ε⊥ remains almost constant. At elevated temperature , K11 increases by ∼50% and K33 decreases by ∼80% compared to pure 5CB when the BC concentration is increased to ∼43 mol % in the mixture. The viscosities increase at room temperature by nearly two orders of magnitude at ∼43 mol %, compared to the corresponding values of pure 5CB. The stiffening of K11 and exorbitantly large enhancement in all the viscosities at a higher mol % of BC indicate that the viscoelastic properties are highly impacted by the presence of smectic clusters of BC molecules that results from the restricted free rotation of the molecules along the bow axis in the nematic phase.
COBISS.SI-ID: 26333479