Modeling dipolar and quadrupolar defect structures generated by chiral islands in freely suspended liquid crystal films

Silvestre, Nuno M.; Patrício, Pedro; Gama, M. M. Telo da; Pattanaporkratana, Apichart; Park, C. S.; Maclennan, Joseph E.; Clark, Noel A.

doi:10.1103/physreve.80.041708

Cited by 16 publications

(12 citation statements)

References 42 publications

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“…As twist distortions are energetically unfavourable in LCs with η < 0, the split-core boojum becomes unstable with respect to the double-core structure. This is in line with the twist transition reported in hyperbolic hedgehog defect cores (see figures 4 and 5 of [50]) on colloids with homeotropic anchoring, and in general, with the effect of elastic anisotropy on the structure of distortions around topological defects in 2D [51].…”

Section: Temperaturesupporting

confidence: 90%

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Liquid crystal boojum-colloids

2012

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Colloidal particles dispersed in a liquid crystal (LC) lead to distortions of the director field. The distortions are responsible for long-range effective colloidal interactions whose asymptotic behaviour is well understood. The short-distance behaviour depends on the structure and dynamics of the topological defects nucleated near the colloidal particles and a full nonlinear theory is required to describe it. Spherical colloidal particles with strong planar degenerate anchoring nucleate a pair of antipodal surface topological defects, known as boojums. We use the Landau-de Gennes theory to resolve the mesoscopic structure of the boojum cores and to determine the pairwise colloidal interactions. We compare the results in three (3D) and two (2D) spatial dimensions for spherical and disc-like colloidal particles, respectively. The corresponding free energy functionals are minimized numerically using finite elements with adaptive meshes. Boojums are always point-like in 2D, but acquire a rather complex structure in 3D, which depends on the combination of the anchoring potential, the radius of the colloid, the temperature and the LC elastic anisotropy. We identify three types of defect cores in 3D that we call single, double and split-core boojums, and investigate the associated structural transitions. The split-core structure is favoured by low temperatures, strong anchoring and small twist to splay or bend ratios. For sufficiently strong anchoring potentials characterized by a well-defined uniaxial minimum, the split-core boojums are the only stable configuration. In the presence of two

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Section: Temperaturesupporting

confidence: 90%

“…Due to the vector nature of the c director, it is possible to distinguish clockwise, anticlockwise or mixed planar anchoring on discs in smC films [51]. The orientation that is realized results from the interplay of the anchoring potential, the c director field in the vicinity of the disc and the LC properties.…”

Section: Free Energy Of Smectic C Filmsmentioning

confidence: 99%

Liquid crystal boojum-colloids

2012

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“…It may explain why Langmuir monolayers composed of multiple chiral molecules demonstrate a limit to domain coarsening (58) and biological lipid rafts are believed to have a finite size (59), in contradiction to continuous coarsening predicted by the CahnHilliard model of phase separation (43). Our description of raftraft repulsion is analogous to the twist-mediated interaction of chiral islands in smectic-C films (60)(61)(62). It offers an explanation for the mutual repulsion observed between transmembrane protein pores formed by certain antimicrobials, if one imagines that these chiral pores impose phospholipid tilt at their interface with the background membrane (63,64).…”

Section: Discussionmentioning

confidence: 89%

Chiral twist drives raft formation and organization in membranes composed of rod-like particles

Kang

Lubensky

2016

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

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Lipid rafts are hypothesized to facilitate protein interaction, tension regulation, and trafficking in biological membranes, but the mechanisms responsible for their formation and maintenance are not clear. Insights into many other condensed matter phenomena have come from colloidal systems, whose micron-scale particles mimic basic properties of atoms and molecules but permit dynamic visualization with single-particle resolution. Recently, experiments showed that bidisperse mixtures of filamentous viruses can self-assemble into colloidal monolayers with thermodynamically stable rafts exhibiting chiral structure and repulsive interactions. We quantitatively explain these observations by modeling the membrane particles as chiral liquid crystals. Chiral twist promotes the formation of finite-sized rafts and mediates a repulsion that distributes them evenly throughout the membrane. Although this system is composed of filamentous viruses whose aggregation is entropically driven by dextran depletants instead of phospholipids and cholesterol with prominent electrostatic interactions, colloidal and biological membranes share many of the same physical symmetries. Chiral twist can contribute to the behavior of both systems and may account for certain stereospecific effects observed in molecular membranes. membrane rafts | liquid crystals | chirality | self-assembly | colloids F ilamentous viruses have proved to be a fruitful colloidal system (1-19). They serve as monodisperse, rigid, and chiral rods that are ∼1 µm in length and interact effectively through hard-core repulsion (2, 7). When suspended in an aqueous solution at increasing concentrations, they transition from a disordered isotropic phase to a cholesteric (chiral nematic) phase characterized by alignment along a director field that twists with a preferred handedness and wavelength (1, 6). The addition of a nonadsorbing polymer such as dextran induces lateral virusvirus attraction via the depletion interaction (10,12,20,21). The viruses self-assemble into monolayers that exhibit fluid-like dynamics internally (10) and sediment to the bottom of glass containers, which are coated with a polyacrylamide brush to suppress depletion-induced virus-wall attractions (22). The rich physics and phenomenology of membranes formed from singlevirus species have been thoroughly studied (8)(9)(10)(11)(12)(13)(14)(15)(16)(17)19). However, two-species membranes demonstrate a novel set of behaviors that are not adequately understood (18). We review these behaviors now before describing a theory that can explain them.fd-Y21M and M13KO7, which we shorten to fd and M13 for convenience, are two species of filamentous virus that have slightly different lengths and form cholesteric phases of opposite handednesses (Table 1 and Fig. 1A). Membranes composed of both fd and M13 viruses are circular with interior particles aligned largely perpendicularly to the membrane plane and edge particles tilted azimuthally, as in single-species membranes (13). At low dextran concentrations, the two spec...

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“…of pattern formation and dynamics of the director field, [4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22] the dynamics of single or paired defects, [23][24][25][26] as well as self-organization of inclusions and their interaction with the surrounding film, see ref. [27][28][29][30][31][32][33][34][35][36] and references in ref. 37.…”

Section: Introductionmentioning

confidence: 99%