O. Yaroshchuk

Transformation of hydrogen bonding of a liquid crystal-aerosil system under the influence of an electric field☆

Abstract The transformation of hydrogen bonds in the liquid crystal (5CB)-aerosil system under the influence of an electric field is investigated with the use of IR spectroscopy methods. It is shown that aerosil addition (10 wt.%) to 5CB leads to the formation of weak hydrogen bonds between the aerosil hydroxyl groups and the π-electrons of benzene rings of 5CB (SiOH ⋯ π). Under the influence of an electric field ( U = 60 V, ƒ = 2 kHz ) these bonds undergo a rearrangement, the 5CB molecules in the aerosil pores aligning along the direction of the electric field and thereby forming a new network of hydrogen bonds.

An Oblique Orientation of Nematic Liquid Crystals on a Photosensitive Aligning Polymer

Abstract The problem of an oblique orientation of a liquid crystal in cells with light induced easy orientation axis is considered. Theoretical and experimental studies of the director distribution in a cell with a photosensitive orientant, fluorinated polyvinylcinnamate polymer film, are performed. The two exposure technique for liquid crystal oblique orientation and the condition for a new anchoring transition in a cell with a photosensitive orientant are also presented.

Electrically Controlled Light Scattering of the Aerosil-Liquid Crystal System

Abstract Optical and electro-optical characteristics of a silica suspension in a liquid crystal were studied. Their possible applications in different electro-optical devices are analyzed.

Polymethacryloylaminoarylmethacrylates: New Concept of Photoalignment Materials for Liquid Crystals

New class of highly efficient polymers for liquid crystal (LC) photoalignment is proposed. These polymers are based on methacryloylaminoarylmethacrylates having two methacryloyl groups of different reactivity. The more active O-methacryloyl group is subjected to polymerization, while the less active NH-methacryloyl group undergoes photocrosslinking reaction in combination with Fries rearrangement. The latter process is anisotropic in case of polarized light irradiation that results in LC photoalignment with readily controlled pretilt angle and anchoring energy. The induced alignment shows high thermal and photo-stability.

Molecular interaction and ‘memory’ of filled liquid crystals

Abstract The dependences of an irreversible response (‘memory’ effect) of 5CB-aerosil suspensions on the chemical composition and concentration of the aerosil and the electric field parameters are investigated. IR-spectra show that hydrogen bonds between the 5CB molecules and aerosil particles play an important role in the occurrence of the ‘memory’ effect.

New Photoalignment Materials in LCD's Development: Liquid Crystal Pretilt Angle Variations By Using Fluoroalkylmethacrylates

Fluorinated copolymers based on 4-(N-methacryloylamino)phenyl methacrylate are proposed as materials for the liquid crystal (LC) photoalignment with a wide range of variations of a pretilt angle. As fluorinated chains, 2,2,3,3-tetrafluoropropylmethacrylate and 2,2,3,3,4,4,5,5-octafluoropenthylmethacrylate are used. The growth of a pretilt angle with the concentration of fluorinated chains, more pronounced in a series with longer fluorinated chain, is observed. The pretilt angle of TN LC ZLI 2293 is smoothly varied in the range 0°–20°. Additionally, the uniform high pretilt angle (89°–90°) alignment is realized for VA LC MJ961180.

Photochemistry of Bis-Methacrylic Polymers and Alignment of Liquid Crystals

Photochemical processes leading to the photoinduced anisotropy and the excellent photoaligning properties of bis-methacrylic polymers are discussed. Comparing the data for bis-methacrylic polymers and a series of model compounds, we conclude that Fries rearrangements and crosslinking reactions taking place in bis-methacrylic polymers cause the photoinduced ordering in films of these polymers via the mechanism of photoselection. Thus, all of these photochemical processes contribute to the liquid crystal photoalignment. The induced alignment is thermally stable due to the crosslinking of methacryloyl groups which fix the induced anisotropy in aligning polymer films.

Influence of the Aerosil Surface Modification on Electro-Optical Characteristics of Filled Liquid Crystals

Abstract We have studied the influence of surface state of aerosil on electro-optical characteristics of suspensions ‘aerosil-liquid crystal (LC)’. Modification of aerosil surface by hydrophobic fragments improves these characteristics. Also the dependence of a hydrophobic modificator structure on electro-optical characteristics was investigated. Explanation is given on the basis of the influence of the surface structure on the anchoring energy value of the LC-aerosil interface.

Kinetic Characteristics of Light Induced Anisotropy and Mechanisms of the Molecular Alignment in Azo Dye Containing Polymer Films

Abstract Induction and relaxation of optical anisotropy in azobenzene containing polymer films under the action of polarized UV-light irradiation are investigated by polarization UV and IR spectroscopy methods. The dependence of anisotropy relaxation on the exposure conditions is established. The results are interpreted supposing the partial ordering of main-chains fragments in irradiated films. A theoretical model explaining experimental results is developed.

Light manipulation of nanoparticles in arrays of topological defects

We report a strategy to assemble and manipulate nanoparticles arrays. The approach is based on the use of topological defects, namely disclination lines, created in chiral liquid crystals. The control of nanoparticle-loaded topological defects by low power light is demonstrated. Large-scale rotation, translation and deformation of quantum dots light-emitting chains is achieved by homogeneous LED illumination. Full reconfigurability and time stability make this approach attractive for future developments and applications.