Long-range structuring of nanoparticles by mimicry of a cholesteric liquid crystal

Abstract

Patterning nano-objects is an exciting interdisciplinary research area in current materials science, arising from new optical and optoelectronic properties and the need to miniaturize electronic components. Many techniques have been developed for assembling nanoparticles into two- and three-dimensional arrays. Most studies involving liquid crystals as templates have dealt with colloidal particles and nematic and smectic phases. Here, we demonstrate the long-range ordering of nanoparticle assemblies that adopt the helical configuration of the cholesteric liquid crystalline phase. Because we used glass-forming cholesterics, the nanostructures could be examined by transmission electron microscopy. The platinum nanoparticles form periodic ribbons that mimic the well-known 'fingerprint' cholesteric texture. Surprisingly, the nanoparticles do not decorate the original cholesteric texture but create a novel helical structure with a larger helical pitch. By varying the molar fraction of cholesterol-containing mesogen in the liquid crystal host, we show that the distance between the ribbons is directly correlated to the pitch. Therefore this inherent lengthscale becomes a simple control parameter to tune the structuring of nanoparticles. These results demonstrate how such an assembly process could be modulated, providing a versatile route to new materials systems.

In Situ and Ex Situ Syntheses of Magnetic Liquid Crystalline Materials: A Comparison

“…This is not straightforward to explain, however it does not seem to be connected to the oxidation state of the particles in the composite since the transition temperatures remains unchanged if the sample is left exposed to the air during three months. Earlier studies have demonstrated a destabilization of the mesophases in physical mixtures of liquid crystal and inorganic nanoparticles, which was attributed to chemisorption effects [20]. On the other hand, a recent example showed that fluxional ligands can provide a certain degree of freedom which allows the LC to preferentially organize itself around the nanoparticles and to improve the LC properties [21].…”

Controlling the Self‐Assembly of Periodic Defect Patterns in Smectic Liquid Crystal Films with Electric Fields

“…Periodic soft materials with spontaneous breaking of translation symmetry such as block copolymers (lamellar, cylindrical, cubic and gyroid phases) [1][2][3] and liquid crystals (smectic, cholesteric and columnar phases) [4][5][6][7][8][9][10] are being actively investigated for creating self-assembled ordered structures and templates for micro and nanoscale applications. Periodic soft materials may help overcome the limits of current microfabrication techniques in terms of easiness, rapidity, cost and spatial resolution, with the added benefi t of a large response to external stimuli.…”

Properties of a Thermotropic Nematic Liquid Crystal Doped with Graphene Oxide

“…[ 1,2 ] The incorporation of various nanomaterials into liquid crystals (LCs), and the complexity of their interaction, have recently attracted much interest. [3][4][5][6][7][8][9][10][11][12] The addition of nanoparticles (NPs) to liquid crystals produces composite materials with additional functionality, and tunable optic, electric, magnetic, or electrooptic properties. Both molecular and macroscopic bulk properties are modifi ed.…”