Nematic Liquid Crystalline Medium Research Articles

Geometrical impacts of platonic particles on nematic liquid crystal dynamics.

Platonic-solid-like particles in liquid crystals offer intriguing opportunities for engineering complex materials with tailored properties. Inspired by platonic solids' geometric simplicity and symmetry, these particles possess well-defined shapes such as cubes, tetrahedra, octahedra, dodecahedra, and icosahedra. When dispersed within nematic liquid-crystalline media, these particles interact with the surrounding medium in intricate ways, influencing the local orientational order of liquid crystal molecules. In this work, we implement continuum simulations to study how the combination of particle shape and surface anchoring gives rise to line defects that follow the edges of the particles and how they are affected by the presence of a Poiseuille flow. Platonic-solid-like particles in liquid crystals have shown promise in diverse applications ranging from photonics and metamaterials to colloidal self-assembly and responsive soft materials.

Deterministic topological defects and quantum dot assembly in a nematic liquid crystalline medium

Liquid crystal (LC) materials exhibit interesting electro-optic switching and molecular ordering properties. Furthermore, the addition of chemically compatible active emitters such as core-shell quantum dots (QD) in a LC medium allows optical as well as dielectric tuning in an anisotropic, reconfigurable ordered medium. Order in a nematic LC phase is characterized by an orientational order parameter. In this work, we demonstrate the use of patterned substrates to generate arrays of integer topological defects in a nematic LC medium doped with cadmium selenide (core) cadmium sulfide (shell) core–shell QDs. We demonstrate the formation of metastable air-pillar-induced integer topological defects (TDs) in relatively thinner 9 μm LC sandwich cells, and the formation of field-induced TDs in thicker (25 μm) cells. Simultaneously, the self-assembly of core-shell QDs into square arrays on the patterned substrates is discussed, highlighting potential electro-optic device applications. The surfactant hexadecyltrimethylammonium bromide (CTAB) is found to play a significant role in LC TD formation as well as QD spatial organization at the optimized concentration. Self-assembly and ordering of single- and multi-component LCs within structured devices is a highly relevant problem for modern optoelectronic devices. This work opens new possibilities for classical as well as quantum light sources which require spatially ordered optical emitters in a reconfigurable dielectric medium at a micron-scale.

Plasmonic gold-cellulose nanofiber aerogels.

Assembly of plasmonic nanomaterials into a low refractive index medium, such as an aerogel, holds a great promise for optical metamaterials, optical sensors, and photothermal energy converters. However, conventional plasmonic aerogels are opaque and optically isotropic composites, impeding them from being used as low-loss or polarization-dependent optical materials. Here we demonstrate a plasmonic-cellulose nanofiber composite aerogel that comprises of well-dispersed gold nanorods within a cellulose nanofiber network. The cellulose aerogel host is highly transparent owing to the small scattering cross-section of the nanofibers and forms a nematic liquid crystalline medium with strong optical birefringence. We find that the longitudinal surface plasmon resonance peak of gold nanorods shows a dramatic shift when probed for the cellulose aerogel compared with the wet gels. Simulations reveal the shift of surface plasmon resonance peak with gel drying can be attributed to the change of the effective refractive index of the gels. This composite material may provide a platform for three- dimensional plasmonic devices ranging from optical sensors to metamaterials.

3-Hydroxy-4-[(phenylimino)methyl]phenyl 4-(Hexadecanoyloxy)benzoate

A new Schiff base ester, 3-hydroxy-4-[(phenylimino)methyl]phenyl 4-(hexadecanoyloxy)benzoate was synthesized and its IR, 1H-NMR, 13C-NMR and MS spectroscopic data are presented.

Dispersions of multi-walled carbon nanotubes in liquid crystals: A physical picture of aggregation

Aggregation of carbon nanotubes dispersed in nematic liquid crystalline medium is discussed. A model assuming that the aggregates consist of a “skeleton” formed by stochastically arranged nanotubes and a “shell” (“coat”) of incorporated and adjacent nematic molecules is proposed. The aggregates of this type can be considered as large quasi-macroscopic particles in the nematic matrix. The resulting composite system is a representative of a new type of complex molecular liquids with self-organization of particles in anisotropic medium. Many essential features and implications of the theoretical model (e.g., effect of concentration, aspect ratio and orientational order parameter of the nanotubes on the size and fractal dimensionality of the aggregates formed, as well as on the rate of aggregation) are in good agreement with experimental data obtained by various physical methods.

On an effective model for ferronematic liquid crystals

AbstractThe tools of homogenization theory are used to develop an effective model for ferronematics–colloidal suspensions of small ferromagnetic particles in a nematic liquid crystalline medium. The results are presented for dilute suspensions of identical prolate spheroidal particles. For needle‐like particles of large eccentricity, the model reduces to a known expression [5]. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Structure of molecules by NMR spectroscopy using liquid crystal solvents

Nuclear magnetic resonance spectroscopy of molecules aligned in nematic liquid crystalline media provides information on the molecular structure and order parameters. The partial alignment of the molecules in the liquid crystalline phases gives rise to residual intramolecular dipolar couplings which are dependent on internuclear distances, and therefore yield information on the structure of molecules. The dipolar couplings are in general large compared to chemical shifts, and the spectra become rapidly complex with the increase in the number of interacting spins and decrease of symmetry of molecules. In this article, the procedure for the analyses of such spectra is outlined in a pedagogical manner. The concept of the order parameter is illustrated in a phenomenological way. The utility of the technique and obtainable information is demonstrated using practical examples. ©1998 John Wiley & Sons, Inc. Concepts Magn Reson 10: 167–192, 1998

Pretilt angle measurements on smectic A cells with chevron and tilted bookshelf layer structures

Abstract We have measured the pretilt angle induced by rubbed polymer films in a smectic A and in a nematic liquid crystalline medium using an optical phase retardation method. The pretilt angle was found to depend on the liquid crystalline phase (smectic A versus nematic) and on the smectic layer structure (chevron versus tilted-bookshelf). The occurrence of the different smectic layer structures was verified by X-ray diffraction measurements. The effect of the applied rubbing energy on the pretilt angle obtained is measured.