Ring-shaped liquid crystal structures through patterned planar photo-alignment

Berteloot, Brecht; Nys, Inge; Poy, Guilhem; Beeckman, Jeroen; Neyts, Kristiaan

doi:10.1039/d0sm00308e

Cited by 27 publications

(33 citation statements)

References 36 publications

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“…We here use these insights to stabilize a new type of topological solitons in NLC cells in which both substrates are patterned. This in contrast to previous works where one patterned substrate was combined with a uniformly aligned substrate [15,26,27]. Solitons, or so-called particle-like topological states, are usually studied in chiral LC samples with strong confinement [31][32][33][34][35][36][37], but photo-alignment techniques allow studying soliton structures in less confined configurations [38] and non-chiral cells [15,26,27].…”

Section: Introductionmentioning

confidence: 97%

“…This in contrast to previous works where one patterned substrate was combined with a uniformly aligned substrate [15,26,27]. Solitons, or so-called particle-like topological states, are usually studied in chiral LC samples with strong confinement [31][32][33][34][35][36][37], but photo-alignment techniques allow studying soliton structures in less confined configurations [38] and non-chiral cells [15,26,27]. We investigate new soliton-like NLC structures induced by well-designed ring-shaped alignment patterns at the confining substrates.…”

Section: Introductionmentioning

confidence: 98%

“…Different illumination techniques (interference illumination, direct write illumination, projection illumination with a spatial light modulator (SLM), plasmonic patterning, etc.) can be used to create alignment patterns with high-resolution and close to arbitrary variations in the preferred azimuthal anchoring at the substrate [10][11][12][13][14][15][16]. This has been successfully applied to create very efficient transmissive and reflective LC flat-optics devices, that are manipulating the so-called geometric (or Pancharatnam-Berry) phase of light.…”

Section: Introductionmentioning

confidence: 99%

“…When a different azimuthal angle is imposed at corresponding locations at the top and bottom substrate, a position dependent twist in the bulk can occur. However, for some combinations of alignment patterns at the substrates, the topology at the interfaces requires either the creation of disclinations in the bulk or regions with vertical director orientation [15,[23][24][25][26][27][28][29][30]. We recently demonstrated for different alignment configurations that surface induced twist conflicts are often elegantly resolved, without the need for singular disclination lines, by introducing a region with vertical director orientation in the bulk of the device [15,[23][24][25].…”

Section: Introductionmentioning

confidence: 99%

“…However, for some combinations of alignment patterns at the substrates, the topology at the interfaces requires either the creation of disclinations in the bulk or regions with vertical director orientation [15,[23][24][25][26][27][28][29][30]. We recently demonstrated for different alignment configurations that surface induced twist conflicts are often elegantly resolved, without the need for singular disclination lines, by introducing a region with vertical director orientation in the bulk of the device [15,[23][24][25]. Honma et al described the same phenomenon as the formation of so-called "thick disclinations" (upon combination of two thin disclinations, without the presence of singularities in the final configuration) and Ouchi et al discussed this phenomenon as the stabilization of nonsingular wall loops [26,28].…”

Section: Introductionmentioning

confidence: 99%

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Surface Stabilized Topological Solitons in Nematic Liquid Crystals

2020

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Photo-alignment is a versatile tool to pattern the alignment at the confining substrates in a liquid crystal (LC) cell. Arbitrary alignment patterns can be created by using projection with a spatial light modulator (SLM) for the illumination. We demonstrate that a careful design of the alignment patterns allows the stabilization of topological solitons in nematic liquid crystal (NLC) cells, without the need for chirality or strong confinement. The created LC configurations are stabilized by the anchoring conditions imposed at the substrates. The photo-aligned background at both substrates is uniformly planar aligned, and ring-shaped regions with a 180° azimuthal rotation are patterned with an opposite sense of rotation at the top and bottom substrate. A disclination-free structure containing a closed ring of vertically oriented directors is formed when the patterned rings at the top and bottom substrate overlap. Thanks to the topological stability, a vertical director orientation in the bulk is observed even when the centra of both patterned rings are shifted over relatively large distances. The combination of numerical simulations with experimental measurements allows identification of the 3D director configuration in the bulk. A finite element (FE) Q-tensor simulation model is applied to find the equilibrium director configuration and optical simulations are used to confirm the correspondence with experimental microscopy measurements. The created LC configurations offer opportunities in the field of optical devices, light guiding and switching, particle trapping and studies of topological LC structures.

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Section: Introductionmentioning

confidence: 97%

Section: Introductionmentioning

confidence: 98%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Surface Stabilized Topological Solitons in Nematic Liquid Crystals

2020

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Nematic Liquid Crystal Disclination Lines Driven by A Photoaligned Defect Grid

Nys

Berteloot

Beeckman

et al. 2021

Advanced Optical Materials

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behavior in the neighborhood of defects and their dynamics. [4] Disclination lines provide a topological stability that can be instrumental for new switching modes, to realize bistable switching, etc. Studying the formation, interaction, and responsiveness of LC disclinations is therefore not only interesting from a theoretical point of view but also opens up new possibilities for technological applications.Disclination lines can connect defects defined at the surface or can form closed loops in the bulk of a NLC, for example when encircling colloidal inclusions, [5] or when rapid but continuous variations in the alignment direction occur independently at opposing substrates of a device. [1d,e,h,i,3c] To realize patterned surface anchoring, scribing, microrubbing, surface topography, pillars, and photoalignment have been used. [1,2] In the case of strong anchoring, a defect in the alignment pattern with charge s generates 2|s| disclination lines in the bulk of the LC. In the case of weak anchoring and gliding, defects can become mobile and disclinations lines may connect two defects of the same charge on opposing substrates. [6] Thanks to photoalignment, stable defects can now easily be realized experimentally, as has been demonstrated in a few papers. [1d,e,3] The flexibility of photoalignment patterning in combination with the stimuli-responsiveness (e.g., electrical tunability) of LCs allows to design disclination networks with preprogrammed functionality. [2b,3c] Enhanced understanding of the LC behavior in cells with 2D patterns of topological defects is however still necessary to successfully engineer functional LC devices such as multistable photonic components, programmable origami or devices with directed self-assembly of colloidal particles. To study the interaction of NLC disclination lines and their behavior under applied voltages, we defined a square grid pattern of ½ defects on the bottom substrate in combination with a uniformly planar aligned top substrate. Different types of interconnections occur between the +1/2 and −1/2 surface defects, and the three most common types of bulk disclinations are analyzed in detail by comparing experiments with numerical simulations (with and without applied voltage). In the discussion section also a theoretical analysis is provided, explaining the curvature of the different disclination lines and including the effect of unequal elastic constants for splay, twist, and bend. To reduce the splay energy, a tilt of the director is induced close to the +1/2 surface defect. We managed to make this visible in the microscope by increasing the tilt under influence of an electric field.Photoalignment for nematic liquid crystals makes it possible to design complex alignment patterns with point defects, that can act as anchoring points for disclination lines. This feature may be used to realize novel electro-optical devices with bistability or enhanced scattering and is promising for material applications such as stimuli-responsive actuators, active matter, and assemb...

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Two‐Step Photoalignment with High Resolution for the Alignment of Blue Phase Liquid Crystal

Liu

Nys

Neyts

2022

Advanced Optical Materials

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The self‐assembling properties of liquid crystal (LC) are ideal for realizing switchable optical components. The director organization is strongly determined by the alignment at the substrate interfaces and photoalignment is a versatile method based on linearly polarized UV light. In this work, a two‐step photoalignment procedure is proposed to pattern the alignment at the surface. Illumination with uniform polarization or with an interference pattern is combined to obtain stripe patterns or square patterns of photoalignment. It can indeed be confirmed that the nematic director follows the varying azimuthal orientation. By increasing the angle between the two interfering beams, photoalignment with sub‐micrometer resolution is obtained, compatible with the dimensions of blue phase (BP) LC unit cell. Homogeneous domains of BP II with (100) or (110) crystal orientation are obtained and their Kossel patterns are recorded. The two‐step photoalignment technique allows to create patterns with high resolution and to control the orientation of BP LC, which is promising for photonic applications that require single domains.

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Ring-shaped liquid crystal structures through patterned planar photo-alignment

Abstract: Ring-shaped planar photo-alignment at the surface gives rise to different 3D liquid crystal configurations in the bulk.

Cited by 27 publications

References 36 publications

Surface Stabilized Topological Solitons in Nematic Liquid Crystals

Surface Stabilized Topological Solitons in Nematic Liquid Crystals

Nematic Liquid Crystal Disclination Lines Driven by A Photoaligned Defect Grid

Two‐Step Photoalignment with High Resolution for the Alignment of Blue Phase Liquid Crystal

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