Ordering nano- and microparticles assemblies with liquid crystals

Blanc, Christophe; Coursault, Delphine; Lacaze, Emmanuelle

doi:10.1080/21680396.2013.818515

Cited by 160 publications

(142 citation statements)

References 179 publications

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“…represents the most dramatic departure of the LC-colloid system from its isotropic counterparts, as the director distortions around the particles bring a number of new facets in the behaviour of colloids, such as anisotropic inter-particle forces 33 , levitation 44 and nonlinear electrophoresis 45 . 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 .…”

Section: Surface Anchoring and Two Types Of Liquid Crystal Colloidsmentioning

confidence: 99%

Transport of particles in liquid crystals

2014

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Section: Surface Anchoring and Two Types Of Liquid Crystal Colloidsmentioning

confidence: 99%

Transport of particles in liquid crystals

2014

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“…In recent years, nanoparticles (NPs) dispersions in liquid crystal (LC) matrices have gained increasing research interest [1,2]. The mixture may show modifications in the elastic and dielectric LC constants [3][4][5], the electro-optical properties [6,7] or the cell conductivity [3,6,8,9].…”

Section: Introductionmentioning

confidence: 99%

The peculiar electrical response of liquid crystal-carbon nanotube systems as seen by impedance spectroscopy

García-García¹,

Vergaz²,

Algorri³

et al. 2015

J. Phys. D: Appl. Phys.

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Conductive nanoparticles, especially elongated ones such as carbon nanotubes, dramatically modify the electrical behavior of liquid crystal cells. These nanoparticles are known to reorient with liquid crystals in electric fields, causing significant variations of conductivity at minute concentrations of tens or hundreds ppm. The above notwithstanding, impedance spectroscopy of doped cells in the frequency range customarily employed by liquid crystal devices, 100 Hz-10kHz, shows a relatively simple resistor/capacitor response where the components of the cell can be univocally assigned to single components of the electrical equivalent circuit. However, widening the frequency range up to 1 MHz or beyond reveals a complex behavior that cannot be explained with the same simple EEC. Moreover, the system impedance varies with the application of electric fields, their effect remaining after removing the field. Carbon nanotubes are reoriented together with liquid crystal reorientation when applying voltage, but barely reoriented back upon liquid crystal relaxation once the voltage is removed. Results demonstrate a remarkable variation in the impedance of the dielectric blend formed by liquid crystal and carbon nanotubes, the irreversible orientation of the carbon nanotubes and possible permanent contacts between electrodes.

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“…As one approaches the "core" of the defect, director deformation becomes so strong that the degree of orientational order varies in space. Disclinations can attract additives, e.g., colloidal particles (3)(4)(5)(6)(7)(8) and even small molecules (9,10). Such an attraction is energetically favored, as the strongly distorted disclination core region is replaced with the additive (4).…”

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Periodic assembly of nanoparticle arrays in disclinations of cholesteric liquid crystals

Prince

Cho

et al. 2017

Proc. Natl. Acad. Sci. U.S.A.

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An important goal of the modern soft matter science is to discover new self-assembly modalities to precisely control the placement of small particles in space. Spatial inhomogeneity of liquid crystals offers the capability to organize colloids in certain regions such as the cores of the topological defects. Here we report two selfassembly modes of nanoparticles in linear defects-disclinations in a lyotropic colloidal cholesteric liquid crystal: a continuous helicoidal thread and a periodic array of discrete beads. The beads form one-dimensional arrays with a periodicity that matches half a pitch of the cholesteric phase. The periodic assembly is governed by the anisotropic surface tension and elasticity at the interface of beads with the liquid crystal. This mode of self-assembly of nanoparticles in disclinations expands our ability to use topological defects in liquid crystals as templates for the organization of nanocolloids. colloidal liquid crystals | nanoparticle self-assembly | liquid crystal droplets | topological defects | anisotropic surface tension T he most extensively studied liquid crystalline phase, the socalled nematic, has been so named after the linear defectdisclinations that appear as flexible threads in optical microscopy textures; "thread" is "ν«μα" in Greek (1, 2). The disclinations represent singularities of the director that describes the local orientation of molecules. As one approaches the "core" of the defect, director deformation becomes so strong that the degree of orientational order varies in space. Disclinations can attract additives, e.g., colloidal particles (3-8) and even small molecules (9, 10). Such an attraction is energetically favored, as the strongly distorted disclination core region is replaced with the additive (4). The unique templating ability of disclinations has stimulated the exploration of their applications, such as the fabrication of optical materials (11), conductive microwires (12), soft magnets (13), and electrooptical devices (5,14,15).Disclinations in nematic liquid crystals are generally onedimensional structures, as the director pattern repeats itself along the line. When an additive is attracted to the disclination core, two possible morphologies are expected: (i) continuous thread-like assembly, or (ii) a linear array of discrete beads. The disclination-templated assemblies reported so far had a threadlike shape, as observed for polymers in the so-called blue phases (15) and for molecular amphiphiles at the cores of nematic disclinations (9, 10).Here, we report the templating behavior of disclinations in the chiral version of the nematic liquid crystal, the so-called cholesteric (Ch) phase. The local directorn in this phase undergoes helicoid twisting around a helical axisv while being perpendicular to this axis (1, 2). Continuous twist leads to a pseudolayered structure, with a well-defined pitch but no modulation of density. Experiments were performed for spherical Ch droplets, in which disclinations correspond to the equilibrium state, thus ensuring...

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Ordering nano- and microparticles assemblies with liquid crystals

Cited by 160 publications

References 179 publications

Transport of particles in liquid crystals

Transport of particles in liquid crystals

The peculiar electrical response of liquid crystal-carbon nanotube systems as seen by impedance spectroscopy

Periodic assembly of nanoparticle arrays in disclinations of cholesteric liquid crystals

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