Spherical nematic shells with a threefold valence

Koning, Vinzenz; López-León, Teresa; Darmon, Alexandre; Fernández‐Nieves, Alberto; Vitelli, Vincenzo

doi:10.1103/physreve.94.012703

Cited by 25 publications

(22 citation statements)

References 34 publications

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“…16(d)]. The simulation results are largely compatible with previous reports on simulations of shells in T configuration [9,[44][45][46].…”

Section: Appendix A: Explanation Of Apparent Oval Shape Of Tangentialsupporting

confidence: 89%

“…Even with well-defined uniform boundary conditions, there may be significant variability in the director field and distribution of topological defects in the shell. This is particularly the case for shells in a T configuration, a situation that has been extensively investigated, experimentally [5,9,13,14,29,44] as well as theoretically and by computer simulation [4,6,[8][9][10][11][44][45][46]. The Poincaré-Hopf theorem dictates that the inside as well as the outside of a T shell must have a total topological defect charge of +2 [1,3].…”

Section: Introductionmentioning

confidence: 99%

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Dynamic tuning of the director field in liquid crystal shells using block copolymers

Noh

Wang

Liang

et al. 2020

Phys. Rev. Research

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When an orientationally ordered system, like a nematic liquid crystal (LC), is confined on a self-closing spherical shell, topological constraints arise with intriguing consequences that depend critically on how the LC is aligned in the shell. We demonstrate reversible dynamic tuning of the alignment, and thereby the topology, of nematic LC shells stabilized by the nonionic amphiphilic block copolymer Pluronic F127. Deep in the nematic phase, the director (the average molecule orientation) is tangential to the interface, but upon approaching the temperature T NI of the nematic-isotropic transition, the director realigns to normal. We link this to a delicate interplay between an interfacial tension that is nearly independent of director orientation, and the configuration-dependent elastic deformation energy of an LC confined in a shell. The process is primarily triggered by the heating-induced reduction of the nematic order parameter, hence realignment temperatures differ by several tens of degrees between LCs with high and low T NI , respectively. The temperature of realignment is always lower on the positive-curved shell outside than at the negative-curved inside, yielding a complex topological reconfiguration on heating. Complementing experimental investigations with mathematical modeling and computer simulations, we identify and investigate three different trajectories, distinguished by their configurations of topological defects in the initial tangential-aligned shell. Our results uncover a new aspect of the complex response of LCs to curved confinement, demonstrating that the order of the LC itself can influence the alignment and thereby the topology of the system. They also reveal the potential of amphiphilic block copolymer stabilizers for enabling continuous tunability of LC shell configuration, opening doors for in-depth studies of topological dynamics as well as novel applications in, e.g., sensing and programed soft actuators.

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“…16(d)]. The simulation results are largely compatible with previous reports on simulations of shells in T configuration [9,[44][45][46].…”

Section: Appendix A: Explanation Of Apparent Oval Shape Of Tangentialsupporting

confidence: 89%

Section: Introductionmentioning

confidence: 99%

Dynamic tuning of the director field in liquid crystal shells using block copolymers

Noh

Wang

Liang

et al. 2020

Phys. Rev. Research

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“…1(b), regardless of the shell geometry. This cholesteric arrangement differs from its nematic counterpart, in which the triangle is not necessarily isosceles [53].…”

Section: Defect Configurations In Cholesteric Shellsmentioning

confidence: 85%

Topological defects in cholesteric liquid crystal shells

et al. 2016

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We investigate experimentally and numerically the defect configurations emerging when a cholesteric liquid crystal is confined to a spherical shell. We uncover a rich scenario of defect configurations, some of them non-existent in nematic shells, where new types of defects are stabilized by the helical ordering of the liquid crystal. In contrast to nematic shells, here defects are not simple singular points or lines, but have a large structured core. Specifically, we observe five different types of cholesteric shells. We study the statistical distribution of the different types of shells as a function of the two relevant geometrical dimensionless parameters of the system. By playing with these parameters, we are able to induce transitions between different types of shells. These transitions involve interesting topological transformations in which the defects recombine to form new structures. Surprisingly, the defects do not approach each other by taking the shorter distance route (geodesic), but by following intricate paths.

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“…It has been experimentally observed that thickness variation can produce a number of novel defect configurations over a spherical liquid-crystal shell [5]. It is of great interest to include the effect of thickness in a generalized Frank free energy model to account for these new experimental observations [23]. This is beyond the scope of this study.…”

Section: Resultsmentioning

confidence: 98%

Curvature-driven stability of defects in nematic textures over spherical disks

Duan

Yao

2017

Phys. Rev. E

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Stabilizing defects in liquid-crystal systems is crucial for many physical processes and applications ranging from functionalizing liquid-crystal textures to recently reported command of chaotic behaviors of active matters. In this work, we perform analytical calculations to study the curvature driven stability mechanism of defects based on the isotropic nematic disk model that is free of any topological constraint. We show that in a growing spherical disk covering a sphere the accumulation of curvature effect can prevent typical +1 and +1/2 defects from forming boojum textures where the defects are repelled to the boundary of the disk. Our calculations reveal that the movement of the equilibrium position of the +1 defect from the boundary to the center of the spherical disk occurs in a very narrow window of the disk area, exhibiting the first-order phase-transition-like behavior. For the pair of +1/2 defects by splitting a +1 defect, we find the curvature driven alternating repulsive and attractive interactions between the two defects. With the growth of the spherical disk these two defects tend to approach and finally recombine towards a +1 defect texture. The sensitive response of defects to curvature and the curvature driven stability mechanism demonstrated in this work in nematic disk systems may have implications towards versatile control and engineering of liquid crystal textures in various applications.

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Spherical nematic shells with a threefold valence

Cited by 25 publications

References 34 publications

Dynamic tuning of the director field in liquid crystal shells using block copolymers

Dynamic tuning of the director field in liquid crystal shells using block copolymers

Topological defects in cholesteric liquid crystal shells

Curvature-driven stability of defects in nematic textures over spherical disks

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