Director-Configurational Transitions around Microbubbles of Hydrostatically Regulated Size in Liquid Crystals

Völtz, Camilla; Maeda, Yasuhiro; Tabe, Yuka; Yokoyama, Hiroshi

doi:10.1103/physrevlett.97.227801

Cited by 40 publications

(24 citation statements)

References 22 publications

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“…The particle size is another parameter to play with in order to modulate the anchoring properties, as reported previously [9,[40][41][42]. Particles smaller (larger) than the typical length K/W ∼ µm, where K is the (average) nematic elastic constant (∼ 10 pN) and W the surface anchoring strength (∼ 5×10 −6 J.m −2 ) [43,44], tend to favor weak (strong) anchoring conditions with a low (high) cost in terms of elastic energy.…”

Section: Introductionmentioning

confidence: 89%

Dispersions of ellipsoidal particles in a nematic liquid crystal

et al. 2014

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Colloidal particles dispersed in a partially ordered medium, such as a liquid crystal (LC) phase, disturb its alignment and are subject to elastic forces. These forces are long-ranged, anisotropic and tunable through temperature or external fields, making them a valuable asset to control colloidal assembly. The latter is very sensitive to the particle geometry since it alters the interactions between the colloids. We here present a detailed numerical analysis of the energetics of elongated objects, namely prolate ellipsoids, immersed in a nematic host. The results, complemented with qualitative experiments, reveal novel LC configurations with peculiar topological properties around the ellipsoids, depending on their aspect ratio and the boundary conditions imposed on the nematic order parameter. The latter also determine the preferred orientation of ellipsoids in the nematic field, because of elastic torques, as well as the morphology of particle aggregates.

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Section: Introductionmentioning

confidence: 89%

Dispersions of ellipsoidal particles in a nematic liquid crystal

et al. 2014

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“…The mathematical description of the interactions between colloidal particles in the nematic crystals is in fact very similar to the electrostatic interaction between the electric charges (13,18), but this simple electrostatic picture breaks-down in some important cases (24). The corresponding director field around the topological dipole is illustrated in Figure 1 Figure 2 shows another possible director configuration, which is of quadrupolar symmetry and a thin defect ring encircles the particle at its equator (25)(26)(27)(28)(29)(30)(31)(32). Such a quadrupolar colloidal particle can be obtained using an appropriate surface preparation technique or adjusting the size of the particle.…”

Section: Topological Dipoles and Quadrupolesmentioning

confidence: 98%

Optical manipulation and self-assembly of nematic colloids: colloidal crystals and superstructures

Muševič

2010

Liquid Crystals Today

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Optical manipulation of colloidal particles in nematic liquid crystals is far more complex than manipulation in water-based colloids. Owing to the long-range nature of the orientational ordering, their elasticity and topological conservation laws, almost any kind of object can be trapped and manipulated in liquid crystals. Furthermore, local heating due to the absorption of light can be used to create microdroplets of the isotropic phase, which interact strongly with colloidal particles. This leads to a broad variety of colloidal assemblies in liquid crystals, which cannot be observed in isotropic solvents: colloidal wires, assembled by entangled topological defects, superstructures in mixtures of large and small colloidal particles and a broad variety of two-dimensional nematic colloidal crystals. In all cases, the colloidal binding energy is several orders of magnitude stronger compared with waterbased colloids. The large variety of colloidal superstructures, which can be assembled in nematic colloids, makes them highly interesting for application in photonic materials.

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“…The topological constraints imposed by our choice of boundary data produce either a line or point singularity in the vicinity of the particle. Theoretical [38,40,41] and experimental [42,43] studies show that a small particle (a/ξ 60) will be encircled by a disclination loop, known as a Saturn ring, whereas a point defect, a hyperbolic hedgehog, will be energetically favorable provided that a/ξ 60. Note that both configurations are axisymmetric with respect to n 0 .…”

Section: A Alignment Tensormentioning

confidence: 99%

Q-tensor model for electrokinetics in nematic liquid crystals

et al. 2017

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We use a variational principle to derive a mathematical model for a nematic electrolyte in which the liquid crystalline component is described in terms of a second-rank order parameter tensor. The model extends the previously developed director-based theory and accounts for presence of disclinations and possible biaxiality. We verify the model by considering a simple but illustrative example of liquid crystal-enabled electro-osmotic flow around a stationary dielectric spherical particle placed at the center of a large cylindrical container filled with a nematic electrolyte. Assuming homeotropic anchoring of the nematic on the surface of the particle and uniform distribution of the director on the surface of the container, we consider two configurations with a disclination equatorial ring and with a hyperbolic hedgehog, respectively. The computed electro-osmotic flows show a strong dependence on the director configurations and on the anisotropies of dielectric permittivity and electric conductivity of the nematic, characteristic of liquid crystal-enabled electrokinetics. Further, the simulations demonstrate space charge separation around the dielectric sphere, even in the case of isotropic permittivity and conductivity. This is in agreement with the induced-charge electro-osmotic effect that occurs in an isotropic electrolyte when an applied field acts on the ionic charge it induces near a polarizable surface.

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Director-Configurational Transitions around Microbubbles of Hydrostatically Regulated Size in Liquid Crystals

Cited by 40 publications

References 22 publications

Dispersions of ellipsoidal particles in a nematic liquid crystal

Dispersions of ellipsoidal particles in a nematic liquid crystal

Optical manipulation and self-assembly of nematic colloids: colloidal crystals and superstructures

Q-tensor model for electrokinetics in nematic liquid crystals

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