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de Oliveira E, Mirantsev L, Lyra M, de Oliveira I. Orientational ordering of active nematics confined to a 2D nanoscopic ring-shaped cavity. J Mol Liq 2023. [DOI: 10.1016/j.molliq.2023.121513] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/24/2023]
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de Araújo CB, de Oliveira EJL, Lyra ML, Mirantsev LV, de Oliveira IN. Formation of topological defects in nematic shells with a dumbbell-like shape. SOFT MATTER 2022; 18:4189-4196. [PMID: 35605981 DOI: 10.1039/d2sm00378c] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/15/2023]
Abstract
The present study investigates dumbbell-shaped nematic liquid crystal shells. Using molecular dynamics (MD) simulations, we consider the effects of an external electric field on nematic ordering by computing the average molecular alignment's time evolution and equilibrium configuration. We show that the number and location of topological defects are strongly affected by the external field, with the orientational ordering's equilibrium configuration depending on field direction about the shell's long axis. For a transverse external field, it is verified that the defect rearrangement presents a non-linear dynamics, with a field independent characteristic time scale delimiting the short and long time regimes. Effects associated with varying the shell's Gaussian curvature are also analyzed.
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Affiliation(s)
- C B de Araújo
- Instituto de Física, Universidade Federal de Alagoas, Maceió, AL, Brazil.
| | - E J L de Oliveira
- Instituto de Física, Universidade Federal de Alagoas, Maceió, AL, Brazil.
| | - M L Lyra
- Instituto de Física, Universidade Federal de Alagoas, Maceió, AL, Brazil.
| | - L V Mirantsev
- Institute for Problems of Mechanical Engineering, Russian Academy of Sciences, St. Petersburg, Russia
| | - I N de Oliveira
- Instituto de Física, Universidade Federal de Alagoas, Maceió, AL, Brazil.
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He K, Zhou Y, Ramezani-Dakhel H, de Pablo JJ, Fernandez-Nieves A, Lopez-Leon T. From nematic shells to nematic droplets: energetics and defect transitions. SOFT MATTER 2022; 18:1395-1403. [PMID: 35103746 DOI: 10.1039/d1sm00241d] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/14/2023]
Abstract
In this work, we investigate the possibility of inducing valence transitions, i.e. transitions between different defect configurations, by transforming a nematic shell into a nematic droplet. Our shells are liquid crystal droplets containing a smaller aqueous droplet inside, which are suspended in an aqueous phase. When osmotically de-swelling the inner droplet, the shell progressively increases its thickness until it eventually becomes a single droplet. During the process, the shell energy landscape evolves, triggering a response in the system. We observe two different scenarios. Either the inner droplet progressively shrinks and disappears, inducing a defect reorganization, or it is expelled from the shell at a critical radius of the inner droplet, abruptly changing the geometry of the system. We use numerical simulations and modeling to investigate the origin of these behaviors. We find that the selected route depends on the defect structure and the energetics of the system as it evolves. The critical inner radius and time for expulsion depend on the osmotic pressure of the outer phase, suggesting that the flow through the shell plays a role in the process.
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Affiliation(s)
- Kunyun He
- Laboratoire Gulliver, UMR 7083 CNRS, ESPCI Paris, PSL Research University, 75005 Paris, France.
| | - Ye Zhou
- Institute for Molecular Engineering, University of Chicago, Chicago, Illinois 60637, USA
| | - Hadi Ramezani-Dakhel
- Institute for Molecular Engineering, University of Chicago, Chicago, Illinois 60637, USA
| | - Juan J de Pablo
- Pritzker School of Molecular Engineering, University of Chicago, Chicago, Illinois 60637, USA
| | - Alberto Fernandez-Nieves
- Department of Condensed Matter Physics, University of Barcelona, 08028 Barcelona, Spain
- ICREA-Institucio Catalana de Recerca i Estudis Avancats, 08010 Barcelona, Spain
| | - Teresa Lopez-Leon
- Laboratoire Gulliver, UMR 7083 CNRS, ESPCI Paris, PSL Research University, 75005 Paris, France.
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Mirantsev LV. Behavior of chiral active nematics confined to nanoscopic circular region. THE EUROPEAN PHYSICAL JOURNAL. E, SOFT MATTER 2021; 44:112. [PMID: 34476624 DOI: 10.1140/epje/s10189-021-00120-y] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/12/2021] [Accepted: 08/26/2021] [Indexed: 06/13/2023]
Abstract
We performed molecular dynamic simulations of a model active nematic confined to a two-dimensional nanoscopic circular region under both tangential and radial anchoring boundary conditions. This active material is assumed to be composed of elongated chiral particles which interact with each other by means of isotropic Lennard-Jones and anisotropic Maier-Saupe-like potentials. These particles have the lateral appendage emitting a jet of some substance generated by a certain internal chemical reaction. As a result, such elongated particles are exposed to both the reactive self-propelled force and the torque that provide an additional translational movement of particles and a self-rotation with respect to their geometric centers. It has been found that the chiral active nematics under consideration form time-dependent vortex-like structures with two +1/2 topological defects which are similar to experimentally observed structures in active materials.
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Affiliation(s)
- L V Mirantsev
- Institute for Problems of Mechanical Engineering, Russian Academy of Sciences, Bolshoi 61, V. O., St., Saint Petersburg, Russia, 199178.
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Ishii Y, Zhou Y, He K, Takanishi Y, Yamamoto J, de Pablo J, Lopez-Leon T. Structural transformations in tetravalent nematic shells induced by a magnetic field. SOFT MATTER 2020; 16:8169-8178. [PMID: 32555908 DOI: 10.1039/d0sm00340a] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/11/2023]
Abstract
The role of applied fields on the structure of liquid crystals confined to shell geometries has been studied in past theoretical work, providing strategies to produce liquid crystal shells with controlled defect structure or valence. However, the predictions of such studies have not been experimentally explored yet. In this work, we study the structural transformations undergone by tetravalent nematic liquid crystal shells under a strong uniform magnetic field, using both experiments and simulations. We consider two different cases in terms of shell geometry and initial defect symmetry: (i) homogeneous shells with four s = +1/2 defects in a tetrahedral arrangement, and (ii) inhomogeneous shells with four s = +1/2 defects localized in their thinner parts. Consistently with previous theoretical results, we observe that the initial defect structure evolves into a bipolar one, in a process where the defects migrate towards the poles. Interestingly, we find that the defect trajectories and dynamics are controlled by curvature walls that connect the defects by pairs. Based on the angle between Bs, the local projection of the magnetic field on the shell surface, and n+½, a vector describing the defect orientations, we are able to predict the nature and shape of those inversion walls, and therefore, the trajectory and dynamics of the defects. This rule, based on symmetry arguments, is consistent with both experiments and simulations and applies for shells that are either homogeneous or inhomogeneous in thickness. By modifying the angle between Bs and n+½, we are able to induce, in controlled way, complex routes towards the final bipolar state. In the case of inhomogeneous shells, the specific symmetry of the shell allowed us to observe a hybrid splay-bend Helfrich wall for the first time.
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Affiliation(s)
- Yoko Ishii
- Department of Physics, Graduate School of Science, Kyoto University, Oiwake-cho, Kitashirakawa, Sakyo-ku, Kyoto, 606-8562, Japan
| | - Ye Zhou
- Pritzker School of Molecular Engineering, University of Chicago, Chicago, Illinois 60637, USA.
| | - Kunyun He
- UMR No. 7083, CNRS, Gulliver, ESPCI Paris, PSL Research University, 10 Rue Vauquelin, 75005 Paris, France.
| | - Yoichi Takanishi
- Department of Physics, Graduate School of Science, Kyoto University, Oiwake-cho, Kitashirakawa, Sakyo-ku, Kyoto, 606-8562, Japan
| | - Jun Yamamoto
- Department of Physics, Graduate School of Science, Kyoto University, Oiwake-cho, Kitashirakawa, Sakyo-ku, Kyoto, 606-8562, Japan
| | - Juan de Pablo
- Pritzker School of Molecular Engineering, University of Chicago, Chicago, Illinois 60637, USA.
| | - Teresa Lopez-Leon
- UMR No. 7083, CNRS, Gulliver, ESPCI Paris, PSL Research University, 10 Rue Vauquelin, 75005 Paris, France.
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