Spatial distribution control of polymer nanoparticles by liquid crystal disclinations

Abstract

A perylene-labeled hyper-branched polymer with a mesogenic shell was observed to migrate toward a field with a large distortion of directors. This polymer was captured by disclination lines of 1/2 strength in its nematic and chiral nematic phases using a confocal fluorescence microscope. In particular, the well-aligned particle array of the hyper-branched polymers was produced by the chiral nematic phase confined in a wedge cell. The hyper-branched polymer with its mesogenic shell was completely dissolved into an isotropic phase. Immediately after a phase transition to the chiral nematic phase, numerous droplets appeared over a wide area owing to phase separation, and the free droplets moved toward the disclination lines via Brownian motion. Finally, the droplets were rapidly attracted to the disclination lines and trapped within them. Polymer Journal (2012) 44, 632-638; doi:10.1038/pj.2012.44; published online 11 April 2012Keywords: confocal fluorescence polarizing microscope; disclination line; fluorescence; hyper-branched polymer; liquid crystal INTRODUCTION Controlling the spatial arrangements of molecules or particles on different length scales is one of the crucial issues of bottom-up nanotechnology. 1,2 Recently, dispersions of colloidal particles and polymers in nematic or cholesteric phases have attracted considerable attention because they demonstrate a diversity of self-assembled arrangements, such as linear or circle chains and 2D lattices. [3][4][5][6] The long-range force of self-assembly originates from the elastic energy of the distortions produced around the particles in the nematic phase. [7][8][9][10][11][12][13][14] The particles have also been observed to be attracted to and to migrate toward a disclination or domain boundary in the nematic field. Because the director distortions of nematic liquid crystals 15,16 are large near the disclination, the elastic energy is higher near the disclination than in uniform director regions. 3 The particles near the disclination might be exposed to an attractive force toward the disclination core, where the highest director gradient is formed.In terms of particle polymers, hyper-branched polymers (HBPs), a novel class of polymer with highly branched structures and large numbers of end groups, are attractive because dendritic chain structures can be produced via an one-pot reaction, and the chemical structure and molecular weight of HBPs can be easily modified. [17][18][19][20][21][22][23] Therefore, the physical properties of the HBPs, such as solubility to a host phase, molecular weight, viscosity, refractive index and fluorescence, can be easily controlled. If the spatial distribution and arrangement of HPBs are further controlled, the range of applications of these materials will expand extensively, especially in photonics and electronics.In this paper, we synthesize perylene-labeled HBPs with mesogenic shells (1) that can be dispersed in a nematic liquid crystal and study

Transport of particles in liquid crystals

“…A rough estimate of the order of magnitude of the elastic energy associated with the director distortions around a strongly anchored micron-size particle placed in an otherwise uniform nematic cell, is 56 . Forces of the same nature are also responsible for attraction of colloidal particles to (particle-free) distortions and defects in the director field in nematics 47,57,58 , smectics [59][60][61] and blue phases 62 , for trapping and ordering of particles at the LC surfaces [63][64][65][66] , and even for symmetry-breaking that enables transport phenomena such as nonlinear electrophoresis in LCs 45,67 . As discussed in the next…”

Blue-phase-polymer-templated nematic with sub-millisecond broad-temperature range electro-optic switching

“…Higashiguchi et al 17 observed spatially periodic polymer networks formed in BPs. Guo et al 18 described a washout refill method to create hyper-reflective chiral nematics, in which the unpolymerized components are washed out and the residual polymer network is refilled with another LC.…”

Fluorescence microscopy reveals molecular localisation at line defects in nematic liquid crystals

“…However, for more quantitative analysis of the molecular localisation, a careful study of the effect of concentration quenching and a detailed understanding of the image formation mechanism in optical microscopy will be required, although the latter problem regarding an anisotropic medium containing sub-resolution-scale spatial inhomogeneity is highly challenging theoretically. Nevertheless, our demonstration of the localisation of low-molecular-weight molecules at liquid crystal defects will help to design complex nanostructures utilizing defects such as those in LC blue phases25 as a template, and will be a step towards the realisation of defect-based micromanipulation and transformable three-dimensional architectures89101112131415 composed of versatile small functional molecules. Moreover, our concept of micromanipulation of LMW molecules by topological defects is applicable to general LCs other than a nematic LC in our study, and therefore offers a means to improve the functionality of a wide variety of LC-based advanced materials, e.g., LC elastomers, colloid-LC composites, and composites with lamellar structures, by introducing functional molecules into the structures.…”

“…Topological defects in NLCs have been known to trap or interact with colloidal and polymer particles891011121314 and therefore offer an intriguing platform for micro-manipulation of small objects in fluid phases, because the position and shape of defects can be externally controlled and modulated, for example, by boundary conditions, an electric field and light. The objects whose manipulation by defects has been reported so far were much larger in size than the NLC molecules, and were attracted by the defects even if the distance between the object and the defect was much larger than the object size.…”