Elementary Edge and Screw Dislocations Visualized at the Lattice Periodicity Level in the Smectic Phase of Colloidal Rods

Repula, Andrii; Grelet, Éric

doi:10.1103/physrevlett.121.097801

Cited by 15 publications

(16 citation statements)

References 38 publications

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“…They appear very large. With the rough assumption that the zone around the dislocation core is transformed into a nematic zone, in agreement with recent results obtained with a screw dislocation [56] and neglecting the elastic nematic distortion within this zone, e dis is the Landau-de Gennes penalty: e dis = 0.73 kT nm −3 , for 8CB at 25 • C [58]. Taking l as 1.8 nm, we need δ ≈ 6nm to reach π(D + 2l)δe dis > 145kT nm −1 which is two times the intra-layer spacing.…”

Section: Discussionsupporting

confidence: 89%

“…The diameter of the dislocation cores, 2r c is generally expected to be close to the dislocation Burgers vector [53,54]. With a Burgers vector b/d = 1, 2r c has indeed been shown to be very close to d for smectic C edge dislocations [55] and for smectic A screw dislocations [56]. If the NPs would induce disorder outside the defect core for the three dislocations of the oily streaks, this would imply that all the dislocation core radii would be smaller than the half of the NP size D + 2l with l the dodecanethiol length in 8CB.…”

Section: Chain Modelmentioning

confidence: 99%

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Interactions Between Topological Defects and Nanoparticles

Missaoui

Coati

et al. 2020

Front. Phys.

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Liquid Crystal (LC) topological defects have been shown to trap nanoparticles (NPs) in the defect cores. The LC topological defects may thus be used as a matrix for new kinds of NP organizations templated by the defect geometry. We here study composites of LC smectic dislocations and gold NPs. Straight NP chains parallel to the dislocations are obtained leading to highly anisotropic optical absorption of the NPs controlled by light polarization. Combining Grazing Incidence Small Angle X-ray scattering (GISAXS), Rutherford Back Scattering (RBS), Spectrophotometry and the development of a model of interacting NPs, we explore the role of the Np size regarding the dislocation core size. We use NPs of diameter D = 6 nm embedded in an array of different kinds of dislocations. For dislocation core larger than the NP size, stable long chains are obtained but made of poorly interacting NPs. For dislocation core smaller than the NP size, the disorder is induced outside the dislocation cores and the NP chains are not equilibrium structures. However we show that at least half of these small dislocations can be filled, leading to chains with strongly enhanced electromagnetic coupling between the NPs. These chains are more probably stabilized by the elastic distortions around the defect cores, the distortion being enhanced by the presence of the grain boundary where the dislocations are embedded.

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Section: Discussionsupporting

confidence: 89%

Section: Chain Modelmentioning

confidence: 99%

Interactions Between Topological Defects and Nanoparticles

Missaoui

Coati

et al. 2020

Front. Phys.

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“…We find for both of them larger values of the height and smaller values of the width as the attraction strength between tips increases. As expected, because the experimental model particles are larger in aspect ratio, their smectic potential height is also larger, due to the increase of stability of the smectic-A phase with increasing aspect ratio [35]. In our theory (Appendix), the shift of the nematic-to-smectic-A phase transition is independent of the volume fraction.…”

Section: Discussionsupporting

confidence: 73%

Self-organization of tip-functionalized elongated colloidal particles

Menegon

Kusters²,

Schoot

2019

Phys. Rev. E

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Weakly attractive interactions between the tips of rodlike colloidal particles affect their liquid-crystal phase behavior due to a subtle interplay between enthalpy and entropy. Here we employ molecular dynamics simulations on semiflexible, repulsive bead-spring chains where one of the two end beads attract each other. We calculate the phase diagram as a function of both the volume fraction of the chains and the strength of the attractive potential. We identify a large number of phases that include isotropic, nematic, smectic-A, smectic-B, and crystalline states. For tip attraction energies lower than the thermal energy, our results are qualitatively consistent with experimental findings: We find that an increase of the attraction strength shifts the nematic to smectic-A phase transition to lower volume fractions, with only minor effect on the stability of the other phases. For sufficiently strong tip attraction, the nematic phase disappears completely, in addition leading to the destabilization of the isotropic phase. In order to better understand the underlying physics of these phenomena, we also investigate the clustering of the particles at their attractive tips and the effective molecular field experienced by the particles in the smectic-A phase. Based on these results, we argue that the clustering of the tips only affects the phase stability if lamellar structures ("micelles") are formed. We find that an increase of the attraction strength increases the degree of order in the layered phases. Interestingly, we also find evidence for the existence of an antiferroelectric smectic-A phase transition induced by the interaction between the tips. A simple Maier-Saupe-McMillan model confirms our findings.

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“…Samples of single-tip functionalized virus suspensions have been prepared by dilution with BisTris-HCl-NaCl buffer, setting the pH at 7 and the ionic strength at 20 mM. These are then studied by optical microscopy [25] and small angle X-ray scattering (SAXS, [20]) (see the Supplemental Material [26]). In our molecular dynamics simulations, we model the chiral filamentous virus particles as achiral overlapping bead-spring chains, where 21 beads are connected via springs of rest length measuring half bead diameter and very large spring constant (Fig.…”

mentioning

confidence: 99%

Directing Liquid Crystalline Self-Organization of Rodlike Particles through Tunable Attractive Single Tips

Repula

Menegon

et al. 2019

Phys. Rev. Lett.

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Compelling justification: Hard-core repulsion is the simplest interaction in Nature yet it drives the self-organization of many complex fluids. To investigate how enthalpy impacts upon entropy-dominated liquid crystalline states, we introduce a highly localized and tunable directional attractive interaction (or "patch") on one of the tips of rod-shaped colloids. Our experiments and computer simulations show that increasing the patch attraction dramatically stabilizes the lamellar phase, a structure desired in materials science due to its outstanding mechanical and optical properties. Our work demonstrates that introducing patches in anisotropic nanoparticles adds to the control of their self-assembly.Abstract: Dispersions of rod-like colloidal particles exhibit a plethora of liquid crystalline states, including nematic, smectic A, smectic B, and columnar phases. This phase behavior can be explained by presuming the predominance of hard-core volume exclusion between the particles.We show here how the self-organization of rod-like colloids can be controlled by introducing a weak and highly localized directional attractive interaction between one of the ends of the particles. This has been performed by functionalizing the tips of filamentous viruses by means of regioselectively grafting fluorescent dyes onto them, resulting in a hydrophobic patch whose attraction can be tuned by varying the number of bound dye molecules. We show, in agreement with our computer simulations, that increasing the single tip attraction stabilizes the smectic phase at the expense of the nematic phase, leaving all other liquid crystalline phases invariant. For sufficiently strong tip attraction the nematic state may be suppressed completely to get a direct isotropic liquid-tosmectic phase transition. Our findings provide insights into the rational design of building blocks for functional structures formed at low densities.

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Elementary Edge and Screw Dislocations Visualized at the Lattice Periodicity Level in the Smectic Phase of Colloidal Rods

Cited by 15 publications

References 38 publications

Interactions Between Topological Defects and Nanoparticles

Interactions Between Topological Defects and Nanoparticles

Self-organization of tip-functionalized elongated colloidal particles

Directing Liquid Crystalline Self-Organization of Rodlike Particles through Tunable Attractive Single Tips

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