Colloidal cholesteric liquid crystal in spherical confinement

Abstract

The organization of nanoparticles in constrained geometries is an area of fundamental and practical importance. Spherical confinement of nanocolloids leads to new modes of packing, self-assembly, phase separation and relaxation of colloidal liquids; however, it remains an unexplored area of research for colloidal liquid crystals. Here we report the organization of cholesteric liquid crystal formed by nanorods in spherical droplets. For cholesteric suspensions of cellulose nanocrystals, with progressive confinement, we observe phase separation into a micrometer-size isotropic droplet core and a cholesteric shell formed by concentric nanocrystal layers. Further confinement results in a transition to a bipolar planar cholesteric morphology. The distribution of polymer, metal, carbon or metal oxide nanoparticles in the droplets is governed by the nanoparticle size and yields cholesteric droplets exhibiting fluorescence, plasmonic properties and magnetic actuation. This work advances our understanding of how the interplay of order, confinement and topological defects affects the morphology of soft matter.

Periodic assembly of nanoparticle arrays in disclinations of cholesteric liquid crystals

“…1C) exhibited characteristic Ch features: a Maltese cross and alternating bright and dark concentric rings corresponding to the twisted directorn (24). The droplets had a core-shell morphology, that is, an isotropic micrometer-size central region (a core) and a Ch shell with a concentric packing of the CNC pseudolayers (24). The average spacing between two adjacent bright or two dark concentric lines of the Ch shell in the POM or BF images corresponded to half-pitch, P/2, of ∼3.1 μm.…”

“…2 C and C' and Movie S1). The equilibrium bead structure was reached via transient states (2,24). The latex beads appeared at the periphery of the droplets, because the spherical concentric Ch-CNC layers started to form at the droplet/oil interface.…”

“…Here, we focus on the lyotropic droplets formed by an aqueous Ch suspension of cellulose nanocrystals (CNCs) and refer to this Ch phase as the Ch-CNC phase. Lyotropic Ch liquid crystals offer a different dimension of applications because (i) they are hydrophilic, in comparison with their hydrophobic thermotropic counterparts, and (ii) the micrometer size of the core of topological defects is significantly larger (24,25) than ∼10-nm core size in droplets of thermotropic liquid crystals (10). The implications of these features are in a potentially broader range of hydrophobicity/ hydrophilicity and sizes of additives templated by disclinations.…”

“…Recently, we have shown (24) that in large (>80-μm diameter) Ch-CNC droplets latex NPs exhibit an intriguing ability to compartmentalize into an isotropic NP-rich droplet core and into the disclinations. In the present work, we show that NP-rich assemblies templated by Ch disclinations can form either continuous (locally cylindrical and globally helicoidal) thread-like structures, or discontinuous, one-dimensional arrays of discrete beads.…”

Temperature-tunable lasing from dye-doped chiral microdroplets encapsulated in a thin polymeric film

“…In recent years, several studies have been published on the CLCs encapsulation in micrometer-sized spherical objects [13]. Inside the microdroplets the CLCs helical structure is preserved and, for boundary planar conditions, the helices axes are radially oriented.…”