Mosaics of topological defects in micropatterned liquid crystal textures

Kim, Dae Seok; Čopar, Simon; Tkalec, Uroš; Yoon, Dong Ki

doi:10.1126/sciadv.aau8064

Cited by 57 publications

(49 citation statements)

References 45 publications

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“…Understanding their behavior is essential for modeling material properties such as plastic deformation and phase transitions, and a great deal of research in soft matter focuses on harnessing topological defects for self-assembly [4][5][6][7][8][9][10]. Liquid crystals (LCs) provide an important arena for the controlled creation of topological defects by geometric frustration, and for the optical observation of these defects at the micron scale [11][12][13][14][15][16]. Many LC materials present multiple liquid crystalline phases, with distinct symmetries, as temperature or concentration is varied [17].…”

Section: Introductionmentioning

confidence: 99%

Topological defects and geometric memory across the nematic–smectic A liquid crystal phase transition

et al. 2019

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We study transformations of self-organized defect arrays at the nematic-smectic A liquid crystal phase transition, and show that these defect configurations are correlated, or "remembered", across the phase transition. A thin film of thermotropic liquid crystal is subjected to hybrid anchoring by an air interface and a water substrate, and viewed under polarized optical microscopy. Upon heating from smectic-A to nematic, a packing of focal conic domains melts into a dense array of boojums-nematic surface defects-which then coarsens by pair-annihilation. With the aid of Landau-de Gennes numerical modeling, we elucidate the topological and geometrical rules underlying this transformation. In the transition from nematic to smectic-A, we show that focal conic domain packings are organized over large scales in patterns that retain a geometric memory of the nematic boojum configuration, which can be recovered with remarkable fidelity. * dbeller@ucmerced.edu †

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Section: Introductionmentioning

confidence: 99%

Topological defects and geometric memory across the nematic–smectic A liquid crystal phase transition

et al. 2019

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“…The vertical orientation of LC director is formed on the electrodes according to the vertically incoming and outgoing electric field. The simulation result indicates that the periodic optical pattern is produced when the LC directors follow the applied electric field, which corresponds to a −1 topological defect in the nematic phase . Furthermore, the crossed electrodes regions are considered as +1 topological defect, so that the total topological charge can be conserved as zero.…”

Section: Resultsmentioning

confidence: 95%

“…Based on these combined results, we recognize that a −1 topological defect resides in the unit of the periodic LC defect pattern . The LC director distribution according to the applied electric field is also estimated using commercial software (Techwize LCD 3D, Sanayi System Company, LTD, Korea) .…”

Section: Resultsmentioning

confidence: 99%

Reconfigurable Periodic Liquid Crystal Defect Array via Modulation of Electric Field

You

Choi

Shin

et al. 2019

Adv Materials Technologies

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Topological defects in liquid crystal (LC) phases have been considered critical from the areas in topology and self‐assembly, as well as in applications such as optical vortex generation, particle manipulation system, and template for material micropatterning. An approach for generating and modulating various patterns of LC defects is presented in a single cell by varying the electrode configurations. Periodic LC defect arrays including −1 topological defect in the nematic phase can be achieved by simply adjusting crossed electrodes. Specifically, the fourfold symmetric −1 defect pattern is used as a vortex beam generator and a particle trapping agent with control either of the frequency of the applied electric field or the temperature. The approach suggested here would be beneficial to extend the use of LC patterns in lithographic tools and optoelectronic devices.

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“…At intermediate frequencies and voltages, it is possible to see a clear transition region between the two states, characterized by a progressive switch from orthogonal to diagonal lattice alignment in the region between four pillars (Figure 6b). A complete switch to a square lattice with diagonal alignment would be possible by changing the pillar array lattice to a hexagonal lattice, as demonstrated by Kim et al [27]. The formation of defect arrays is highly dependent on the ratio of the cell thickness d to the pillar spacing p. When p > 2d, the relation p ~ ml can be satisfied in certain ranges of voltages and frequencies.…”

Section: Effect Of Square-shaped Pillars On the Defect Array Formationmentioning

confidence: 99%

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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Mosaics of topological defects in micropatterned liquid crystal textures

Abstract: Temperature-driven formation of kaleidoscopic mosaics of topological defects is achieved in micropatterned liquid crystals.

Cited by 57 publications

References 45 publications

Topological defects and geometric memory across the nematic–smectic A liquid crystal phase transition

Topological defects and geometric memory across the nematic–smectic A liquid crystal phase transition

Reconfigurable Periodic Liquid Crystal Defect Array via Modulation of Electric Field

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

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