Stable and Metastable Patterns in Chromonic Nematic Liquid Crystal Droplets Forced with Static and Dynamic Magnetic Fields
Spherical confinement of nematic liquid crystals leads to the formation of equilibrium director field configurations that include point and line defects. Driving these materials with flows or dynamic fields often results in the formation of alternative metastable states. In this article, we study th...
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doaj-df6f94797f5046caa05746e748c56c702020-11-25T01:40:49ZengMDPI AGCrystals2073-43522020-02-0110213810.3390/cryst10020138cryst10020138Stable and Metastable Patterns in Chromonic Nematic Liquid Crystal Droplets Forced with Static and Dynamic Magnetic FieldsJordi Ignés-Mullol0Marc Mora1Berta Martínez-Prat2Ignasi Vélez-Cerón3R. Santiago Herrera4Francesc Sagués5Departament de Ciència de Materials i Química Física, Universitat de Barcelona, 08028 Barcelona, SpainDepartament de Ciència de Materials i Química Física, Universitat de Barcelona, 08028 Barcelona, SpainDepartament de Ciència de Materials i Química Física, Universitat de Barcelona, 08028 Barcelona, SpainDepartament de Ciència de Materials i Química Física, Universitat de Barcelona, 08028 Barcelona, SpainDepartament de Ciència de Materials i Química Física, Universitat de Barcelona, 08028 Barcelona, SpainDepartament de Ciència de Materials i Química Física, Universitat de Barcelona, 08028 Barcelona, SpainSpherical confinement of nematic liquid crystals leads to the formation of equilibrium director field configurations that include point and line defects. Driving these materials with flows or dynamic fields often results in the formation of alternative metastable states. In this article, we study the effect of magnetic field alignment, both under static and dynamic conditions, of nematic gems (nematic droplets in coexistence with the isotropic phase) and emulsified nematic droplets of a lyotropic chromonic liquid crystal. We use a custom polarizing optical microscopy assembly that incorporates a permanent magnet whose strength and orientation can be dynamically changed. By comparing simulated optical patterns with microscopy images, we measure an equilibrium twisted bipolar pattern within nematic gems that is only marginally different from the one reported for emulsified droplets. Both systems evolve to concentric configurations upon application of a static magnetic field, but behave very differently when the field is rotated. While the concentric texture within the emulsified droplets is preserved and only displays asynchronous oscillations for high rotating speeds, the nematic gems transform into a metastable untwisted bipolar configuration that is memorized by the system when the field is removed. Our results demonstrate the importance of boundary conditions in determining the dynamic behavior of confined liquid crystals even for configurations that share similar equilibrium bulk structures.https://www.mdpi.com/2073-4352/10/2/138liquid crystalslyotropicchromonicdefectsconfinement effectsemulsions |
collection |
DOAJ |
language |
English |
format |
Article |
sources |
DOAJ |
author |
Jordi Ignés-Mullol Marc Mora Berta Martínez-Prat Ignasi Vélez-Cerón R. Santiago Herrera Francesc Sagués |
spellingShingle |
Jordi Ignés-Mullol Marc Mora Berta Martínez-Prat Ignasi Vélez-Cerón R. Santiago Herrera Francesc Sagués Stable and Metastable Patterns in Chromonic Nematic Liquid Crystal Droplets Forced with Static and Dynamic Magnetic Fields Crystals liquid crystals lyotropic chromonic defects confinement effects emulsions |
author_facet |
Jordi Ignés-Mullol Marc Mora Berta Martínez-Prat Ignasi Vélez-Cerón R. Santiago Herrera Francesc Sagués |
author_sort |
Jordi Ignés-Mullol |
title |
Stable and Metastable Patterns in Chromonic Nematic Liquid Crystal Droplets Forced with Static and Dynamic Magnetic Fields |
title_short |
Stable and Metastable Patterns in Chromonic Nematic Liquid Crystal Droplets Forced with Static and Dynamic Magnetic Fields |
title_full |
Stable and Metastable Patterns in Chromonic Nematic Liquid Crystal Droplets Forced with Static and Dynamic Magnetic Fields |
title_fullStr |
Stable and Metastable Patterns in Chromonic Nematic Liquid Crystal Droplets Forced with Static and Dynamic Magnetic Fields |
title_full_unstemmed |
Stable and Metastable Patterns in Chromonic Nematic Liquid Crystal Droplets Forced with Static and Dynamic Magnetic Fields |
title_sort |
stable and metastable patterns in chromonic nematic liquid crystal droplets forced with static and dynamic magnetic fields |
publisher |
MDPI AG |
series |
Crystals |
issn |
2073-4352 |
publishDate |
2020-02-01 |
description |
Spherical confinement of nematic liquid crystals leads to the formation of equilibrium director field configurations that include point and line defects. Driving these materials with flows or dynamic fields often results in the formation of alternative metastable states. In this article, we study the effect of magnetic field alignment, both under static and dynamic conditions, of nematic gems (nematic droplets in coexistence with the isotropic phase) and emulsified nematic droplets of a lyotropic chromonic liquid crystal. We use a custom polarizing optical microscopy assembly that incorporates a permanent magnet whose strength and orientation can be dynamically changed. By comparing simulated optical patterns with microscopy images, we measure an equilibrium twisted bipolar pattern within nematic gems that is only marginally different from the one reported for emulsified droplets. Both systems evolve to concentric configurations upon application of a static magnetic field, but behave very differently when the field is rotated. While the concentric texture within the emulsified droplets is preserved and only displays asynchronous oscillations for high rotating speeds, the nematic gems transform into a metastable untwisted bipolar configuration that is memorized by the system when the field is removed. Our results demonstrate the importance of boundary conditions in determining the dynamic behavior of confined liquid crystals even for configurations that share similar equilibrium bulk structures. |
topic |
liquid crystals lyotropic chromonic defects confinement effects emulsions |
url |
https://www.mdpi.com/2073-4352/10/2/138 |
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