Defect structures and torque on an elongated colloidal particle immersed in a liquid crystal host

Andrienko, Denis; Allen, Michael; Skačej, Gregor; Žumer, S.

doi:10.1103/physreve.65.041702

Cited by 91 publications

(75 citation statements)

References 33 publications

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“…The field of colloidal emulsions deals with macroscopic distances, and here we are interested in macroscopic colloid-wall separations of an order of micrometers. Until recently, the problem of calculating a mechanical torque on a particle near a nematic liquid crystal surface and its energy has been specified by a particular shape, anchoring, and orientation of the particle, and thus could be addressed only numerically [68,69]. The theory [57,58] developed above considerably simplifies the problem.…”

Section: The Mirror Image Methods Of Colloidal Nematostaticsmentioning

confidence: 99%

Colloidal nematostatics

Pergamenshchik¹,

Uzunova²

2010

Condens. Matter Phys.

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We give a review of the theory of large distance colloidal interaction via the nematic director field. The new area of nematic colloidal systems (or nematic emulsions) has been guided by the analogy between the colloidal nematostatics and electrostatics. The elastic charge density representation of the colloidal nematostatics [V.M. Pergamenshchik, V.O. Uzunova, Eur. Phys. J. E, 2007, 23, 161; Phys. Rev. E, 2007, 76, 011707] develops this analogy at the level of charge density and Coulomb interaction. The analogy is shown to lie in common mathematics based on the solutions of Laplace equation. However, the 3d colloidal nematostatics substantially differs from electrostatics both in its mathematical structure and physical implications. The elastic charge is a vector fully determined by the torque exerted upon colloid, the role of Gauss' theorem is played by conservation of the torque components. Elastic multipoles consist of two tensors (dyads). Formulas for the elastic multipoles, the Coulomb-like, dipole-dipole, and quadrupole-quadrupole pair interaction potentials are derived and illustrated by particular examples. Based on the tensorial structure, we list possible types of elastic dipoles and quadrupoles. An elastic dipole is characterized by its isotropic strength, anisotropy, chirality, and its longitudinal component. An elastic quadrupole can be uniaxial and biaxial. Relation between the multipole type and its symmetry is discussed, sketches of some types of multipoles are given. Using the mirror image method of electrostatics as a guiding idea, we develop the mirror image method in nematostatics for arbitrary director tilt at the wall. The method is applied to the charge-wall and dipole-wall interaction. : 61.30.Dk, 61.30.Jf, 82.70Dd, 01.55.+b 1. The intrigue of nematic colloids: similarity to the electrostatics, its origin, and how it is developed in this article. Key words: nematic colloid, electrostatic analogy, elastic charge and multipoles PACSIsotropic liquids doped with colloidal particles or just colloids are the classical many-particle systems which, over many decades , have been studied using the methods of molecular and statistical physics, electrolyte theory, physical chemistry, and so on [1,2]. Colloidal particles can be of different physical and chemical origin, but in all cases their interaction via isotropic liquid is of a short range [3], even if the colloids are charged since their electric field is rapidly screened by a numerous couterions. The nematic colloids, that have become widely known just over the last 15 years, are fundamentally different: interaction of colloids mediated by distortions of the nematic director is of a long range. That is why nematic colloids are usually compared not with standard isotropic colloids, but with a system of electric charges. The similarity with the electrostatics has always been a powerful, if not dominating, factor of the development of the field of nematic colloids. But what is the origin of this similarity?The interaction of particles in a ne...

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Section: The Mirror Image Methods Of Colloidal Nematostaticsmentioning

confidence: 99%

Colloidal nematostatics

Pergamenshchik¹,

Uzunova²

2010

Condens. Matter Phys.

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“…In one constant approximation L 1 is related to the splay K 11 Both, and L 1 can be obtained experimentally-in this work we chose these parameters to correspond to the physical properties of 5CB. 29 The choice of the nematic potential will dictate the bulk value of the scalar order parameter.…”

Section: ͑8͒mentioning

confidence: 99%

“…Systems of LCs and one or two colloids have been studied by experimental, 4 -8 simulation, [9][10][11][12][13][14] and theoretical methods [15][16][17][18][19][20][21][22][23][24] in connection with their associated defect structures and effective interactions. The simplest case corresponds to a single spherical colloid embedded in a nematic fluid, with strong homeotropic ͑perpendicular͒ anchoring at the colloid surface.…”

Section: Introductionmentioning

confidence: 99%

Interactions between spherical colloids mediated by a liquid crystal: A molecular simulation and mesoscale study

Kim

Guzmán

Grollau

et al. 2004

The Journal of Chemical Physics

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Monte Carlo simulations and dynamic field theory ͑DyFT͒ are used to study the interactions between dilute spherical particles, dispersed in nematic and isotropic phases of a liquid crystal. A recently developed simulation method ͑expanded ensemble density of states͒ was used to determine the potential of mean force ͑PMF͒ between the two spheres as a function of their separation and size. The PMF was also calculated by a dynamic field theory that describes the evolution of the local tensor order parameter. Both methods reveal an overall attraction between the colloids in the nematic phase; in the isotropic phase, the overall attraction between the colloids is much weaker, whereas the repulsion at short range is stronger. In addition, both methods predict a new topology of the disclination lines, which arises when the particles approach each other. The theory is found to describe the results of simulations remarkably well, down to length scales comparable to the size of the molecules. At separations corresponding to the width of individual molecular layers on the particles' surface, the two methods yield different defect structures. We attribute this difference to the neglect of density inhomogeneities in the DyFT. We also investigate the effects of the size of spherical colloids on their interactions.

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“…1 These long-range colloidal interactions are mediated by particle-induced deformations of a LC director n (a unit vector representing the average orientation of mesogenic molecules) that typically propagate to large distances and can be partially "shared" by colloids to minimize elastic energy. 2 The ensuing elasticity-mediated self-assembly of monodisperse microspheres, 1,[3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20] spherical nanoparticles, 21,22 cylindrical colloids, [23][24][25][26][27][28] and particles with more exotic shapes [29][30][31][32][33][34][35][36] has been explored. However, possible applications of this type of colloidal self-assembly in fabrication of mesoscale metaldielectric composites with novel properties will require the use of particles having dissimilar shapes, sizes, and chemical compositions.…”

Section: Introductionmentioning

confidence: 99%

Elastic interactions between colloidal microspheres and elongated convex and concave nanoprisms in nematic liquid crystals

Senyuk¹,

Smalyukh

2012

Soft Matter

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We study mutual alignment and interactions between colloidal particles of dissimilar shapes and dimensions when dispersed in a nematic host fluid. Convex pentagonal and concave starfruitshaped nanoprisms and microspheres induce dipolar or quadrupolar director structures. The ensuing elastic pair interactions between microspheres and nanoprisms are highly dependent on the nanoparticle shape being omnidirectionally attractive for convex prisms but strongly anisotropic for concave prisms. Elastic deformations due to spherical particles cause well-defined alignment of complex-shaped nanoparticles at distances much larger than the microsphere size.We characterize distance and angular dependencies of elastic pair interaction forces, torques, and binding energies. The studied elasticity-mediated self-assembly of metal and dielectric nanoparticles with dissimilar shapes and sizes opens new possibilities for self-assembly based fabrication of structured mesoscopic composites with predesigned properties.

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Defect structures and torque on an elongated colloidal particle immersed in a liquid crystal host

Cited by 91 publications

References 33 publications

Colloidal nematostatics

Colloidal nematostatics

Interactions between spherical colloids mediated by a liquid crystal: A molecular simulation and mesoscale study

Elastic interactions between colloidal microspheres and elongated convex and concave nanoprisms in nematic liquid crystals

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