Effects of silica nanoparticles on electro-optical properties of polymer-stabilized liquid crystals

Effects of Composition and Polymerization Conditions on the Electro-Optic Performance of Liquid Crystal-Polymer Composites Doped with Ferroelectric Nanoparticles

The presence of a polymer network and/or the addition of ferroelectric nanoparticles to a nematic liquid crystal are found to lower transition temperatures and birefringence, which indicates reduced orientational order. In addition, the electro-optic switching voltage is considerably increased when a polymer network is formed by in situ polymerization in the nematic state. However, the resulting polymer network liquid crystal switches at similar voltages as the neat liquid crystal when polymerization is performed at an elevated temperature in the isotropic state. When nanoparticle dispersions are polymerized at an applied DC voltage, the transition temperatures and switching voltages are reduced, yet they are larger than those observed for polymer network liquid crystals without nanoparticles polymerized in the isotropic phase.

Frequency-Driven Self-Organized Helical Superstructures Loaded with Mesogen-Grafted Silica Nanoparticles

Adding colloidal nanoparticles into liquid-crystal media has become a promising pathway either to enhance or to introduce novel properties for improved device performance. Here we designed and synthesized new colloidal hybrid silica nanoparticles passivated with a mesogenic monolayer on the surface to facilitate their organo-solubility and compatibility in a liquid-crystal host. The resulting nanoparticles were identified by 1 H NMR spectroscopy, TEM, TGA, and UV/Vis techniques, and the hybrid nanoparticles were doped into a dual-frequency cholesteric liquid-crystal host to appraise both their compatibility with the host and the effect of the doping concentration on their electro-optical properties. Interestingly, the silica-nanoparticle-doped liquid-crystalline nanocomposites were found to be able to dynamically self-organize into a helical configuration and exhibit multi-stability, that is, homeotropic (transparent), focal conic (opaque), and planar states (partially transparent), depending on the frequency applied at sustained low voltage. Significantly, a higher contrast ratio between the transparent state and scattering state was accomplished in the nanoparticle-embedded liquid-crystal systems.

Controlling liquid crystal pretilt angle with photocurable prepolymer and vertically aligned substrate

We demonstrate a new approach to control the pretilt angle of liquid crystals (LCs) with photocurable prepolymer in a cell fabricated with vertically aligned substrates. During UV exposure, prepolymer approaches and is polymerized on the substrate surfaces because of the vertical phase separation induced by differences in the surface tensions of the employed materials. After polymerization, the polymer structure formed on the substrate alters its surface polarity and changes the pretilt angle of the LC cell. The LC pretilt angle can be controlled from 87.3° to 2.5° when the prepolymer concentration ranges from 0 wt% to 2.5 wt%.