Tunable Dynamic Topological Defect Pattern Formation in Nematic Liquid Crystals

Kim, Min Su; Serra, Francesca

doi:10.1002/adom.201900991

Cited by 39 publications

(51 citation statements)

References 34 publications

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“…Finally, defects can be directly manipulated via external fields, such as optical tweezers [2], electric fields [22], or both [23]. alignment to both the pillars and the ITO, following the procedure outlined in [22,24]. A CCN-mn (Δn = 0.03) mixture consisted of CCN-47 and CCN-55 (Nematel GmbH & Co. KG, Mainz, Germany), nematic at room temperature (Figure 1a).…”

Section: Introductionmentioning

confidence: 99%

“…We note that it is possible to adjust the birefringence of the LC mixture by adding NCB-53 (Δn = 0.149) ( Figure 1b) to the CCN-mn mixture to optimize the optical property [24]. Here, for the diffraction experiments we used a mixture with 25% CCN-47, 25% CCN-55, and 50% NCB-53.…”

Section: Introductionmentioning

confidence: 99%

“…Sasaki and colleagues showed that it is possible to dynamically control the orientation of the array by locally annealing the LC in the isotropic phase with optical laser tweezers and then slowly allowing the system to relax to the orientation that propagates from the edges as the LC is cooled into the nematic phase [22]. The method works well and it controls defects over several hundreds of microns, but it is not easily scalable and relies on the direct intervention of the laser tweezers.Our research proposes instead to use topography in combination with an external applied field [24]. The square defect array is stabilized by an array of micropillars.…”

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confidence: 99%

“…To ensure the high conductivity of LC necessary for the formation of the defect pattern, we added a small amount (<1 wt%) of tetra butyl ammonium benzoate (TBABE) into the LC. We spin-coated a fluorinated polymer, CYTOP (Figure 1c), which gives the homeotropic Crystals 2020, 10, 314 3 of 12 alignment to both the pillars and the ITO, following the procedure outlined in [22,24]. A CCN-mn (∆n = 0.03) mixture consisted of Mainz, Germany), nematic at room temperature (Figure 1a).…”

mentioning

confidence: 99%

“…Our research proposes instead to use topography in combination with an external applied field [24]. The square defect array is stabilized by an array of micropillars.…”

mentioning

confidence: 99%

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Topological Defect Arrays in Nematic Liquid Crystals Assisted by Polymeric Pillar Arrays: Effect of the Geometry of Pillars

Kim

Serra

2020

Crystals

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Topological defects that spontaneously occur in condensed matter and structured fluids such as liquid crystals are useful for their elastic and optical properties, but often the applicability of defect arrays to optics and photonic devices relies on the regularity and tunability of the system. In our recent work [Adv. Opt. Mater. 8, 1900991 (2020)], we showed the formation of regular, reconfigurable, and scalable patterns by exploiting the elastic response of a defect array in liquid crystals in the presence of a polymeric pillar array. In this work, we experimentally investigate the role of size and shape of the pillars on the defect array. We find that the pillar size and geometry provide additional means to regulate the response time, the threshold voltage for the defects’ formation, and the spatial arrangement of the defects.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

mentioning

confidence: 99%

mentioning

confidence: 99%

“…Our research proposes instead to use topography in combination with an external applied field [24]. The square defect array is stabilized by an array of micropillars.…”

mentioning

confidence: 99%

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Topological Defect Arrays in Nematic Liquid Crystals Assisted by Polymeric Pillar Arrays: Effect of the Geometry of Pillars

Kim

Serra

2020

Crystals

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A General Control Strategy to Micropattern Topological Defects in Nematic Liquid Crystals Using Ionically Charged Dielectric Surface

Sasaki

Takahashi

Yokokawa

et al. 2021

Adv Materials Inter

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materials such as colloids, [1][2][3] blockcopolymers, [4][5][6] and liquid crystals. [7][8][9][10][11] Especially the structural and optical anisotropy in nematic liquid crystals (NLCs) are useful for stimuli-responsive applications. NLCs are characterized by a spontaneous orientational order of elongated molecules, called the director, which is denoted by a unit vector n. The director field is influenced by the surface boundary (anchoring) effect and by external fields such as electric, magnetic fields, and temperature. In recent years, many efforts have been made to fabricate microstructures with complex and periodic director fields using various approaches. [9,10,[12][13][14][15] In patterning the director field in two dimensions, the geometrical limitation often induces topological defects which are promising for optoelectronic devices [16][17][18][19] and soft actuators. [20][21][22][23][24][25] Thus, the stabilization and the precise control of n are essentially required for engineering defects toward further development. [26][27][28] Conventionally, it is known that defects can be stabilized by curved surfaces such as colloids [29][30][31][32] otherwise they annihilate over time. [33][34][35] When the NLC sample is sandwiched between two parallel glass substrates, the local director field must be controlled by surface modification techniques. [14,[36][37][38][39] Coating substrates with a polymer layer is a common process to designate n at the surface either to orient in the surface normal direction or to lie in the surface plane. In controlling n using the surfaces between parallel substrates, so far, attentions are mostly paid to the boundary condition of the coating materials on which NLC molecules contact, but meanwhile the thickness of the alignment layer, i.e., the electrical insulation of the alignment layer is not a main concern. The influence of the electrical resistivity of the alignment layer remains unwatched. On the other hand, recently, we have found a micropattern formation of an ion-doped NLC which generates a square array of topological defects under an AC electrical voltage. The pattern formation is spontaneously derived using a perfluoro polymer surface. [40] The phenomenon can be extended to optical applications by combining surface fabrication technique. [13,41] Contrary to the conventional understanding, the obtained results suggest that

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Dynamic Motions of Topological Defects in Nematic Liquid Crystals under Spatial Confinement

Pawale

Swain

Hashemi

et al. 2023

Adv Materials Inter

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Topological defects (TDs) have become a sensational topic due to their significant influence on the unusual optical and physiochemical characteristics of the material. To facilitate their application across a wide range of disciplines it is desirable to analyze and gain fundamental understanding of TDs in both equilibrium and nonequilibrium systems. Liquid crystals (LCs) are considered an ideal system for study given the direct visualization of TDs and a straightforward analyzation process. In addition to the equilibrium morphology of LC TDs, it is also of great interest to track and control the formation and annihilation of defects during thermodynamic processes. However, controlling the dynamic behavior of formed defects remains a challenge. Here, nematic LCs confined in a cell exhibiting surfaces with periodic anchoring conditions containing surface topography are relied on. The effects of patterned surface characteristics such as width, periodicity, and degree of curvature on defects dynamic motion, stabilization, and annihilation are explored. The computational experiments recapitulate the TDs transition path and provide free energy‐based predictions of critical distances for defect annihilation. Taken together, this simple approach offers a promising opportunity to control the dynamics of TDs in LCs through chemical patterned surfaces with topography.

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Tunable Dynamic Topological Defect Pattern Formation in Nematic Liquid Crystals

Cited by 39 publications

References 34 publications

Topological Defect Arrays in Nematic Liquid Crystals Assisted by Polymeric Pillar Arrays: Effect of the Geometry of Pillars

Topological Defect Arrays in Nematic Liquid Crystals Assisted by Polymeric Pillar Arrays: Effect of the Geometry of Pillars

A General Control Strategy to Micropattern Topological Defects in Nematic Liquid Crystals Using Ionically Charged Dielectric Surface

Dynamic Motions of Topological Defects in Nematic Liquid Crystals under Spatial Confinement

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