Change of Liquid-Crystal Domains by Vibrational Excitation for a Columnar Mesophase (original) (raw)
Related papers
Photoalignment of Liquid Crystals by Liquid Crystals
Physical Review Letters, 2000
We observed light-induced alignment of the nematic liquid crystal, 4,4'-n-pentylcyclobiphenyl (5CB), on a fused quartz surface covered with a layer of adsorbed 5CB molecules. Irradiation of the adsorbed layer with polarized ultraviolet light produced homogeneous alignment in a 5CB-filled liquid crystal cell with the axis of easy orientation perpendicular to the polarization direction. The measured anchoring energy increases with illumination, with an observed maximum of 10 -4 erg/cm 2 . Measurements of the phase retardation of polarized light revealed light-induced anisotropy in the irradiated, adsorbed 5CB layer. In addition, pretilt measurements showed near planar alignment of the LC in a cell, while the polarization dependence of second harmonic generation (SHG) suggested a near normal alignment of the first layer. The results suggest that light-induced rearrangement or photo-transformation of 5CB molecules adsorbed on the quartz surface causes the observed phenomenon.
Photoalignment of Liquid Crystalline Materials
Photoalignment of Liquid Crystalline Materials, 2008
Photoalignment possesses significant advantages in comparison with the usual 'rubbing' treatment of the substrates of liquid crystal display (LCD) cells as it is a non-contact method with a high resolution. A new technique recently pioneered by the authors of this book, namely the photo-induced diffusion reorientation of azodyes, does not involve any photochemical or structural transformations of the molecules. This results in photoaligning films which are robust and possess good aligning properties making them particularly suitable for the new generation of liquid crystal devices. Photoalignment of Liquid Crystalline Materials covers state-of-the-art techniques and key applications, as well as the authors' own diffusion model for photoalignment. The book aims to stimulate new research and development in the field of liquid crystalline photoalignment and in so doing, enable the technology to be used in large scale LCD production. • Provides a full examination of the mechanisms of photoalignment. • Examines the properties of liquid crystals during photoalignment, with particular reference made to the effect on their chemical structure and stability. • Considers the most useful photosensitive materials and preparation procedures suitable for liquid crystalline photoalignment. • Presents several methods for photoalignment of liquid crystals. • Compares various applications of photoalignment technology for in-cell patterned polarizers and phase retarders, transflective and micro displays, security and other liquid crystal devices. Through its interdisciplinary approach, this book is aimed at a wide range of practising electrical engineers, optical engineers, display technologists, materials scientists, physicists and chemists working on the development of liquid crystal devices. It will also appeal to researchers and graduate students taking courses on liquid crystals or display technologies. The Society for Information Display (SID) is an international society, which has the aim of encouraging the development of all aspects of the field of information display. Complementary to the aims of the society, the Wiley-SID series is intended to explain the latest developments in information display technology at a professional level. The broad scope of the series addresses all facets of information displays from technical aspects through systems and prototypes to standards and ergonomics Vladimir G. Chigrinov obtained his PhD degree in solid-state physics from the Shubnikov Institute of Crystallography, USSR Academy of Sciences, in 1978. In 1988, he defended his doctoral degree and became a professor at the Shubnikov Institute of Crystallography, where he was a leading researcher from 1996. He joined HKUST in 1999 and is currently an associate professor. Since 1974 Professor Chigrinov has published 2 books. 15 reviews and book chapters, about 150 journal papers, more than 300 conference presentations, and holds more than 50 patents and patent applications in the field of liquid crystals. He is a Senior SID Member, SID Fellow and an Associate Editor of the Journal of the Society for Information Display. Vladimir M. Kozenkov graduated from the Moscow Energetic Institute as a scientist in applied physical optics (laser department). For 30 years he worked at the Organic Intermediates and Dyes Institute (NIOPIK) in Moscow. He pioneered research and development of various organic photosensitive materials for holography, waveguide, integral and polarization optics, stereolithography, optical memory, imaging processing, and security applications. He was the first to discover the phenomenon of photoinduced birefringence in polyvinyl-cinnamate films in 1977. He has published more than 100 refereed papers and holds more than 50 patents. Hoi-Sing Kwok obtained his PhD degree in applied physics from Harvard University in 1978. He joined the State University of New York at Buffalo in 1980 and became a full professor in 1985. He joined HKUST in 1992 an is currently Director of the Center for Display Research ( www.cdr.ust.hk). Professor Kwok has written over 500 refereed publications and holds 40 patents in laser optics and LCD technologies. He is a Fellow of the OSA, the IEEE, and the SID.
Journal of Photochemistry and Photobiology A: Chemistry, 2011
Liquid crystals photoalignment on the films of several side-chain azobenzene-containing polymers with various molecular structures was studied. Kinetics of the alignment and realignment of the liquid crystals director under irradiation by the polarized light was investigated and a comparison of the rates of polymers' azobenzene moieties reorientation and director realignment were performed. The degree of the orientation, stability of the alignment, the possibility of multiple reorientation and other parameters of the photoinduced processes occurring in polymers films and liquid crystal cells were studied in detail. A rubbing technique was applied as alternative method for LC-alignment using these azobenzenecontaining polymers. It was shown that the studied azobenzene-containing polymers can be considered as a photocontrollable command surfaces for the application in display technology and optoelectronics.
Photo-Orientation of Liquid Crystals on Azo Dye-Containing Polymers
Polymers, 2021
In this communication, we summarise our results related to light-induced orientational phenomena at liquid crystal–polymer interfaces. We investigated photoalignment for various nematics at the interface with the photosensitive polymer layer polymethyl methacrilate functionalised with azo dye Disperse Red 1. It was found that the efficiency of photoalignment exhibits marked differences depending on the structure of the rigid core of the liquid crystal molecules. It was demonstrated that the photo-orientation process is also significantly affected by the type of mesophase in which irradiation is carried out. The observations highlight the importance of the mutual influence of the polymer and the liquid crystal in light-induced processes.
Hidden photoalignment of liquid crystals in the isotropic phase
2001
The effects of light-induced alignment and reorientation of liquid crystals LC's have been the subject of intense research over the last decade because of the astonishing science and the extremely promising innovative applications 1–4. One of the most interesting aspects of photoalignment is the possibility of producing an easy-orientation axis on a nonphotosensitive surface in a LC cell upon irradiation by polarized laser light. This effect was first observed in cells filled with dye-doped nematic LC's 5, 6.
Photomanipulation of the anchoring strength of a photochromic nematic liquid crystal
Physical Review E, 2002
The behavior of the Fréedericksz threshold voltage of a planarly oriented sample filled with liquid crystalline azobenzene material possessing a nematic phase is investigated under UV illumination. It is found that the anchoring strength strongly decreases with the UV-exposure time due to the photoisomerization process that takes place in the sample. The changes in the anchoring strength are due to a selective adsorption of cis isomers at the surface. We show that the experimental data can be explained by a model that takes into account the changes in the molecular shape and in the net molecular dipole moment due to the cis-trans isomerization. We obtain a good agreement between the predictions of the model and the experimental data.
Molecular Frustration of Chemically Linked Rod-Disc Liquid Crystal under an Electric Field
Chemistry of Materials, 2010
Molecular orientation of a chemically linked rod-disk (cyanobiphenyl-triphenyl) liquid crystalline (LC) molecule (RD12, where 12 is a number of carbon atoms in each alkyl chain linkage between the rod and the disk mesogens) in an antiparallel rubbed LC cell was investigated under vertically applied alternative current (AC) electric fields. Upon varying vertical AC electric fields from the initial state (0 V) to a fixed voltage ranging between 2.5 and 5.0 V, it was found that RD12 responded to the electric field with two-steps. The rod mesogen having a higher dipole interaction first aligned parallel to the electric field, while the disk mesogen behaved like an anchor of RD12. After the frustration and stabilization of rod mesogens, the in-plane axis of disk mesogen also aligned parallel to the electric field. Based on our experimental results, it was concluded that the peculiar molecular frustrations of RD12 under the vertical AC electric field occurred in a consequence of the competition among rods attached to both sides of the disk molecule. Furthermore, because molecular orientation of RD12 exhibiting a large birefringence is controlled by an electric field, RD12 can be used as a tunable optical switching material in the electro-optical devices.
Physical Review E, 2000
The adsorption kinetics and orientational ordering of 4Ј-n-octyl-4-cyanobiphenyl ͑8CB͒ liquid crystal films evaporated onto photosensitive poly͑vinyl-cinnamate͒ ͑PVCN͒ substrates were investigated by surface optical second-harmonic generation. The adsorption rate of the first monolayer decreases with increasing degree of photochemical modification of the polymer. The in-plane orientational anisotropy of the 8CB films grown on unidirectionally photopolymerized PVCN substrates is considerably lower than the intrinsic surface orientational anisotropy of these substrates, which can explain the generally found weak surface anchoring of liquid crystals on PVCN alignment layers.
2001
In this annual report, we present our recent research results of the anchoring energetic, molecular alignment and field-induced re-orientation in a thin LC film on varying polymeric alignment layers. The photo-induced anisotropy on a photo-alignment film can be controlled by varying the exposure of incident linearly-polarized ultraviolet light. The resulting anchoring properties were studied with optical retardance-voltage (RV), optical transmission-voltage (TV) measurements, polarized infrared absorption spectroscopy and Raman scattering spectroscopy. Our results indicate that the surface anchoring energy on a UV-defined layer can be as large as that on a rubbed polymeric surface. In addition, the anchoring energy in a twist nematic cell can not be decomposed into a simple summation of azimuthal and polar anchoring terms. The LC molecules in a twist pi-cell were found to