Dynamic Orthogonal Switching of a Thermoresponsive Self‐Organized Helical Superstructure

Zhang, Lingli; Wang, Ling; Hiremath, Uma S.; Bisoyi, Hari Krishna; Nair, Geetha G.; Yelamaggad, C. V.; Urbas, Augustine; Bunning, Timothy J.; Li, Quan

doi:10.1002/adma.201700676

Cited by 63 publications

(55 citation statements)

References 27 publications

(16 reference statements)

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“…Nematic liquid crystals (NLCs) have unique electro‐optic properties and in particular chiral nematic liquid crystals (CLCs) can be used in a variety of applications such as mirror‐less lasing, tunable diffraction gratings, color filters, lenses, displays, etc . Their self‐organization into supramolecular structures together with their responsiveness to external stimuli offers them unique functional properties . Being able to control the alignment of LCs and especially CLCs on a micrometer‐scale is therefore extremely important, both from a fundamental and an application‐oriented point of view.…”

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confidence: 99%

Periodic Planar‐Homeotropic Anchoring Realized by Photoalignment for Stabilization of Chiral Superstructures

Nys

Chen

Beeckman

et al. 2018

Advanced Optical Materials

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polar and azimuthal anchoring at an interface allows us to obtain periodic stripes with planar and homeotropic anchoring with two-beam UV interference. The method is based on a mixture of homeotropic alignment material and azo-based photoalignment material illuminated with a periodic pattern of linearly polarized UV light. To the best of our knowledge, this is the first demonstration of controlling azimuthal versus polar anchoring by a maskless UV interference illumination method. In the past, reversible switching between uniform homeotropic and planar alignment was demonstrated by using cis-trans photoisomerization and patterned homeotropic and planar alignment was achieved by depositing self-assembled monolayers of molecules. [4] Chen et al. also established a photoalignment technique that makes use of a mixture of nanoparticles and azo-dyes in the LC. [5] In order to stabilize a lying helix structure, different methods were used to obtain a similar periodic anchoring: a polyimide layer with planar alignment was coated with a chromium complex surfactant for homeotropic anchoring and patterned by hard-contact photolithography. [3a] Alternatively, a mixture with photoreactive cholesteric monomer was spincoated on top of an alignment layer with large pretilt and photopolymerized. [3b] The photoalignment technique that we propose here is mask-less, allows high resolution and is based on the deposition of a single layer and therefore excels in versatility and ease of realization compared to previously reported methods. We expect that a further optimization of the technique can lead to full control of the azimuthal and polar alignment properties on a micrometer scale. This is not only interesting for the aforementioned applications but has very promising applications in geometrical phase optics and can lead to improved control over the mechanical response of liquid crystal elastomers. [6] Moreover, Qian and Sheng found that spatially varying alignment can lead to multiple-degenerate orientational states in the bulk and that the effective anchoring strength can be tuned by varying the alignment texturing. [7] Additionally, the rewritability of photoalignment materials might allow an in situ optical manipulation and reorientation of the LC structures. In combination with stimuli-responsive LCs this may lead to a wealth of new possibilities. Both light stimuli, thermal stimuli and electrical stimuli have proven to be very promising for different applications. [2] CLC in bulk spontaneously forms periodic helical structures and the distance over which the molecular director rotates Self-organization of chiral superstructures in liquid crystal (LC) materials is a powerful tool in developing functional devices based on soft matter. The control and manipulation of the helical axis orientation in chiral nematic liquid crystals are currently attracting significant attention, but are hindered by limited control over the anchoring at the interfaces. The development of new alignment techniques with local control over polar ...

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confidence: 99%

Periodic Planar‐Homeotropic Anchoring Realized by Photoalignment for Stabilization of Chiral Superstructures

Nys

Chen

Beeckman

et al. 2018

Advanced Optical Materials

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“…[274] The chiral switch possesses high change in helical twisting power under temperature variation, presenting handedness inversion at a certain temperature. [274] The chiral switch possesses high change in helical twisting power under temperature variation, presenting handedness inversion at a certain temperature.…”

Section: Thermally Switched Cholesteric Lc Gratingsmentioning

confidence: 99%

Dynamic Control of Light Direction Enabled by Stimuli‐Responsive Liquid Crystal Gratings

et al. 2018

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the duality consolidation, the idea of controlling light and how it interacts with matter has always been an exciting topic. Visible light, as we perceive it, is a small portion of the electromagnetic spectrum composed of mutually perpendicular oscillating electric and magnetic fields that propagate through space and presents wave-like and particle-like behavior. Since the elements comprising matter possess dynamic electron clouds, the electromagnetic nature of light prompts different responses when it interacts with different materials, depending on its intensity, frequency, the arrangement of molecules, and so on. Whenever light interacts with matter, it might be absorbed, re-emitted, scattered, or transmitted. Although these effects are well known, the combination of them with new, innovative materials pushes optics forward. In fact, advances in optics have often occurred through the development of materials with improved optical properties, thus creating remarkable applications that tremendously influence our daily lives. These exciting applications include image processing and recording, lasing, data storage, display devices, detector systems, propulsion systems, and optical tweezers, which have enabled remote micromanipulation of colloidal particles and promising applications in various biomedical and biological applications. [1][2][3] There is, however, one component that stands out: the diffraction grating. It is generally regarded as one of the most important devices in the development of several fields of science. [4] Such importance comes from the fact that a diffraction grating is a device with a periodic structure capable of changing the propagation and splitting the spectrum The ability to control light direction with tailored precision via facile means is long-desired in science and industry. With the advances in optics, a periodic structure called diffraction grating gains prominence and renders a more flexible control over light propagation when compared to prisms. Today, diffraction gratings are common components in wavelength division multiplexing devices, monochromators, lasers, spectrometers, media storage, beam steering, and many other applications. Next-generation optical devices, however, demand nonmechanical, full and remote control, besides generating higher than 1D diffraction patterns with as few optical elements as possible. Liquid crystals (LCs) are great candidates for light control since they can form various patterns under different stimuli, including periodic structures capable of behaving as diffraction gratings. The characteristics of such gratings depend on several physical properties of the LCs such as film thickness, periodicity, and molecular orientation, all resulting from the internal constraints of the sample, and all of these are easily controllable. In this review, the authors summarize the research and development on stimuli-controllable diffraction gratings and beam steering using LCs as the active optical materials. Dynamic gratings fabricated by applying external f...

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“…Recently, multivariant controlling methods have been proposed to effectively tune the hierarchical architectures of CLCs 39b,74. Accordingly, such CLC gratings are endowed with a wide tunability of grating period and rotation, which is highly promising in beam steering applications …”

Section: Photonic Applicationsmentioning

confidence: 99%

Light‐Activated Liquid Crystalline Hierarchical Architecture Toward Photonics

Zheng

et al. 2019

Advanced Optical Materials

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remarkable structure results in a helical-variant dielectric tensor, thus contributing to a natural 1D photonic crystal. [7] It is endowed with a broadband Bragg reflection with a unique circular-polarization selectivity. Blue phase (BP) is another fantastic phase with 3D stacked lattice ( Figure 1D). [8] Such an elegant state-of-matter is energetically preferred in a high chirality system, commonly existing in a narrow temperature range of less than 1 K, between the cholesteric and isotropic phases. It has an exotic arrangement characteristic of LCs, which twists around two helical axes forming cylinders including hierarchically twisted molecular architectures. Such double twisted cylinders are impossible to tile the whole 3D space, which leads to inevitable disclinations and results in frustrated structures.Self-organization is an intrinsic ability of LC molecules. However, the precise control and generation of large-area desirable hierarchical superstructures require state-of-the-art techniques that usually combine the "top-down" microfabrication with the "bottom-up" self-assembly. Here, we review various hierarchical architectures in SLCs, CLCs, and BPLCs, especially recent progresses in light-activated LC hierarchical superstructures, as well as their optics and photonics applications in optics and photonics. In this review, we will see the controllable spatial smectic layer curving via 2D anchoring confinement, 3D topographic confinement, and external field guidance, with which the domain size, shape, orientation, and lattice symmetry of focal conic domain (FCD) arrays are well manipulated. The control of helix direction or fluctuation of CLC layers and the growth of unique fingerprint textures including spiral and wave-like continuous gratings are presented. The 3D manipulation of BPLC hierarchical architecture is accomplished photoalignment and various light-driven azobenzene molecular motors. The construction of these unique hierarchical superstructures brings new opportunities to the design of novel optic and photonic devices. Corresponding applications, including traditional microlens array, beam steering, and more advanced specific optical field generation and LC lasers are comprehensively reviewed as well.

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Dynamic Orthogonal Switching of a Thermoresponsive Self‐Organized Helical Superstructure

Cited by 63 publications

References 27 publications

Periodic Planar‐Homeotropic Anchoring Realized by Photoalignment for Stabilization of Chiral Superstructures

Periodic Planar‐Homeotropic Anchoring Realized by Photoalignment for Stabilization of Chiral Superstructures

Dynamic Control of Light Direction Enabled by Stimuli‐Responsive Liquid Crystal Gratings

Light‐Activated Liquid Crystalline Hierarchical Architecture Toward Photonics

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