Phase Transition-Driven Nanoparticle Assembly in Liquid Crystal Droplets

Abstract

When nanoparticle self-assembly takes place in an anisotropic liquid crystal environment, fascinating new effects can arise. The presence of elastic anisotropy and topological defects can direct spatial organization. An important goal in nanoscience is to direct the assembly of nanoparticles over large length scales to produce macroscopic composite materials; however, limitations on spatial ordering exist due to the inherent disorder of fluid-based methods. In this paper we demonstrate the formation of quantum dot clusters and spherical capsules suspended within spherical liquid crystal droplets as a method to position nanoparticle clusters at defined locations. Our experiments demonstrate that particle sorting at the isotropic–nematic phase front can dominate over topological defect-based assembly. Notably, we find that assembly at the nematic phase front can force nanoparticle clustering at energetically unfavorable locations in the droplets to form stable hollow capsules and fractal clusters at the droplet centers.

Inhomogeneous nematic-isotropic phase transition of a thermotropic liquid crystal doped with iron oxide nanoparticles

“…Colloidal NPs dispersed in LC matrices have been shown to create topological defects in the anisotropic host fluid, especially when spherically shaped NPs are suspended in the nematic medium [10]. In this case, the frustration of the nematic order tends to assemble the dispersed NPs into aggregates to minimize the elastic energy cost [11]. In equilibrium, the local deformation energy of the nematic matrix is related to the anchoring energy of the LC molecules on the NP surface and the effect of NP aggregation.…”

“…In general, when the NP doping ratio increases, more NPs accumulate at the topological defects of the host LC [12]. Furthermore, the NP aggregation can also be driven by the phase transition of the LC media [11,13]. All these phenomena can be utilized to implement selfassembly templates for NP superstructures [14,15].…”

Fabrication and Characterization of Nanoenergetic Hollow Spherical Hexanitrostibene (HNS) Derivatives

“…Spherization nanotechnology has always been considered as a significant method to enhance micro morphology, control micro structure and transform the properties of materials for potential applications [ 17 , 18 , 19 , 20 ]. Especially in the field of energetic materials, the spherization of nanoenergetic materials, which is of great benefit to improve free-flowing properties of the material, to optimize particle gradation, avoid cracking, further increase the charge density and even the detonation energy, has been widely studied and developed [ 14 , 21 , 22 , 23 , 24 , 25 ].…”

Dynamic Spirals of Nanoparticles in Light-Responsive Polygonal Fields

“…19 While dispersions of micro-and nanoparticles in chiral liquid crystals have been described, 20 most investigations of selfassembled patterns are restricted to colloidal particles or to the formation of two-dimensional architectures from particle-like structures. 21 Once incorporated in liquid crystals, nanoparticles form aggregates that fail to mirror any liquid-crystalline organization, [22][23][24][25][26][27][28][29][30][31][32] except for one series of investigations templating the self-assembly of metallic nanoparticles with cholesteric fingerprints. 33,34 In a few examples, the shape, [22][23][24] orientation 22-24-or the pattern geometry 32 of larger aggregates were found to be dependent from a liquid crystalline environment, while bulk liquid crystals doped with nanoparticles are known to reorient under an electric field 35 and light.…”

“…33,34 In a few examples, the shape, [22][23][24] orientation 22-24-or the pattern geometry 32 of larger aggregates were found to be dependent from a liquid crystalline environment, while bulk liquid crystals doped with nanoparticles are known to reorient under an electric field 35 and light. 36 As an alternative to bulk systems, localized topological structures have been used as energetic traps for nanoparticles, in a variety of chiral and non-chiral liquid crystals, ranging from nematic 25,26 to cholesteric droplets, 27,37 blue phases, 28,29 smectic films, 38,39 liquid crystal colloids 30 and liquid crystals in toroidal geometries. 35 Arrays of topological structures carrying trapped nanoparticles were reorganized by driving each of the topological elements individually, 40 but precise control over such topological structures in dynamic liquid crystals remains unaccounted for.…”