Full‐Polymer Cholesteric Composites for Transmission and Reflection Holographic Gratings

Ryabchun, Alexander; Sakhno, Oksana; Stumpe, Joachim; Bobrovsky, Alexey

doi:10.1002/adom.201700314

Cited by 24 publications

(17 citation statements)

References 62 publications

(72 reference statements)

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“…For example, relatively thick composite films can act as an effective light‐scattering medium with tunable characteristics. Light scattering from the composite originates from the mismatch of the refractive indices of elastic matrix (1.49 as measured using Abbe refractometer) and polymer PAAzo (≈1.60). Since the photo‐orientation process is faster than the photodeformation and both can be addressed selectively, there are two ways to control optical properties of light scattering: (i) by controlling the birefringence of the material and (ii) by controlling microparticles shape.…”

Section: Resultsmentioning

confidence: 99%

“…Materials and Composite Preparation : The copolymer PAAzo with a molar ratio of mesogenic and azobenzene side groups of 1:1 was synthesized by free radical polymerization of appropriate monomers which have been obtained according to previously described procedures . The reaction was carried out in anhydrous benzene in a sealed tube under argon atmosphere with the initiator AIBN (2 wt%) for 100 h at 70 °C.…”

Section: Methodsmentioning

confidence: 99%

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Photocontrollable Deformations of Polymer Particles in Elastic Matrix

Ryabchun

Bobrovsky

2019

Advanced Optical Materials

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into mechanical motion or work, such as photoactuation. [1][2][3][4][5] The funda mental importance of these phenomena occurring under the action of light, such as photofluidization, [6][7][8][9][10][11] photoimmo bilization, [6,12,13] formation of surface relief gratings, [14][15][16][17] and other complex 3D structures [10,[18][19][20][21][22][23][24] can help to develop photo responsive materials for versatile applications and will also improve and extend our knowledge in soft matter.The most extensively studied photo active materials usually contain azoben zene moieties as the lightresponsive unit. The properties of azobenzene such as high quantum yield and reversibility of E-Z photoisomerization, high fatigue resis tance, and large changes in molecular shape and dipole moment upon isomerization make it uniquely suitable as an active unit. Molecular shape changes of azobenzene can be harnessed on a macroscopic level by the embedding active molecules into hierarchically organized matter [25] and by confinement of the photoactive material in space, such as, spherical colloids which can selfassemble into 2D and 3D structures (photonic crys tals). The preparation and study of spherical micrometersized particles based on azobenzene polymers have been reported in a number of recent works revealing the importance for various optical microdevices, photonics, microfluidics, etc. [26][27][28][29][30][31][32][33][34][35][36][37][38] It has been demonstrated that polarized light irradiation results in elongation of these particles along the light polarization. Despite the interest to the research area, several issues like the mechanism and reversibility of microscopic shape changes are still elusive. Moreover, there are no reports on the influence of liquid crystal line (LC) ordering on the shapeshifting and optical properties of the particles, as well as the operation of microparticles has never been exploited to build materials with macroscopic functionalities.In the current work, we have developed a novel elastic composite material containing shapereconfigurable parti cles based on liquid crystalline polymer. We have used sty rene-ethylene-butylene-styrene triblock copolymer (SEBS, Figure 1a) as the elastic matrix which provides large deforma tion and low mechanical stiffness [39] and does not interfere to the deformation of embedded particles. Another important role of the matrix is its elasticity responsible for the compres sive forces experienced by the deformed particles which makes possible the shape to recover. The particles are made of liquid crystal copolymer PAAzo bearing mesogenic and azobenzene One of the key challenges of material science currently is the design of multifunctional "smart" materials combining features from both molecular and supramolecular levels. Pursuing the strategy of amplification and transduction of light-induced motion of small molecules (photoswitches) across increasing length scales to macroscopic level, a novel polymer composite based on shapereconfigurable microparticles is desig...

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Section: Resultsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Photocontrollable Deformations of Polymer Particles in Elastic Matrix

Ryabchun

Bobrovsky

2019

Advanced Optical Materials

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“…The second approach is based on photo‐orientation process of mesogenic groups induced by polarized light and related to the rotational diffusion of the azobenzene groups in direction perpendicular polarization plane of the incident light. The photo‐orientation process itself is well studied in a number of papers and was successfully used for the optical photorecording as well as DGs formation by holographic technique …”

Section: Light‐generated Cholesteric Dgsmentioning

confidence: 99%

“…Since then several papers were published demonstrating important characteristics of the holographic recording on cholesteric systems combining the selective light reflection intrinsic to the cholesteric mesophase and photoinduced DGs . In particular, the possibility of multiple photorecording in cholesteric copolymers, mixtures with chiral‐photochromic dopant and polymer–polymer composites was demonstrated. For this purpose, the mixture of nematic azobenzene‐containing copolymer 14 (Figure b) with chiral‐photochromic dopant 9 (Figure c) was prepared and studied.…”

Section: Light‐generated Cholesteric Dgsmentioning

confidence: 99%

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Cholesteric Liquid Crystal Materials for Tunable Diffractive Optics

Ryabchun

Bobrovsky

2018

Advanced Optical Materials

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188

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refractive, diffraction and optical fiber components. In particular, diffraction grating (DG) is one of the key elements for the design and creation of modern optoelectronic devices. One of the most prominent materials for the creation of DGs is liquid crystals. The main feature of these systems is that liquid crystals combine properties such as optical anisotropy inherent for crystals and molecular mobility. High sensitivity to an external field, in particular to an electric field, makes liquid crystals very useful for the creation of DGs with tunable properties. The combination of these properties enables easy control of optical characteristics of such systems and opens wide perspectives for the design of new materials for diffractive optics.Among the different types of liquid crystalline (LC) phases, cholesteric liquid crystal (CLC) phase possesses intrinsic periodicity in the form of the helical supramolecular structure (Figure 1). With the realization of definite alignment conditions, this periodicity has been exploited for generation of DGs. [8,9] Another remarkable feature of the cholesteric mesophase is selective light reflection with the reflection wavelength determined by the simple Equation (1) where n is the average refractive index, and P is the helix pitch. The specific value of helix pitch depends on the chemical structure of the molecules forming the cholesteric phase and concentration of chiral moieties. One of the easiest ways to obtain the cholesteric mesophase is by doping the nematic matrix with chiral components (Figure 1). Variation of structure of chiral molecules by external stimuli leading, for examples, to the photoisomerization, is effectively used for fine tuning of the helix pitch. [10][11][12][13][14][15][16][17] In addition, the application of an electric field also provides a convenient opportunity to change optical properties of the CLC phase. [18][19][20][21] These unique properties enable to design a great variety of optical elements and devices based on CLC layers, films, or cells. Among them it is necessary to mention the media for photo-optical data recording, [22][23][24][25] electrically switchable mirrors, [26,27] optically controllable linearpolarization rotators, [28] coatings with controllable friction and adhesion, [29] materials for display technology, [23,30] secure Modern optics and photonics constantly require break-through materials and designs in order to achieve miniature, lightweight, highly tunable, and effective optical devices. One of the basic optical components is the diffraction grating (DG), widely used for the dispersion of light, beam steering, etc. This review gathers research efforts on diffractive optical elements based on cholesteric liquid crystal (CLC) materials with a supramolecular helical architecture. All main types and fabrication approaches of periodic diffractive structures from CLCs are classified and described. Key optical properties of DGs, their advantages and drawbacks are considered. Special attention is paid on the tunability of DG...

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3D Helix Engineering in Chiral Photonic Materials

et al. 2019

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Engineering the helical structure of chiral photonic materials in three dimensions remains a challenge. 3D helix engineered photonic materials are fabricated by local stratification in a photopolymerizable chiral nematic liquid crystal. The obtained chiral photonic materials reflect both handedness of circular polarized light and show super‐reflectivity. Simulations match the experimentally observed photonic properties and reveal a distorted helical structure. 3D engineered polymer films can be made that reflect both left‐ and right handed circular and linear polarized light dependent and exhibit a changing color contrast upon altering the polarization of incident light. Hence, these 3D engineered photonic materials are of interest for new and emerging applications ranging from anti‐counterfeit labels and data encryption to aesthetics and super‐reflective films.

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Full‐Polymer Cholesteric Composites for Transmission and Reflection Holographic Gratings

Cited by 24 publications

References 62 publications

Photocontrollable Deformations of Polymer Particles in Elastic Matrix

Photocontrollable Deformations of Polymer Particles in Elastic Matrix

Cholesteric Liquid Crystal Materials for Tunable Diffractive Optics

3D Helix Engineering in Chiral Photonic Materials

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