Author: Publisher: ISBN: Category : Languages : en Pages :
Book Description
Abstract : A positive nematic liquid crystal (5CB) sample is confined in cylindrical cells under strong or weak axial anchoring boundary conditions when a radial nonuniform low-frequency electric field is applied and the flexoelectric effect is taken into account. Based on the Frank elastic free energy, the surface energy of the Rapini–Papoular approximation, the polarization free energy and the flexoelectric free energy caused by electric field, we obtain the free energy density of the nematic and solve the corresponding Euler–Lagrange equation numerically. We investigate the director distribution, the critical voltage and the critical exponent of nematic liquid crystal in cylindrical cells. It follows that the critical exponent is the classical one. It is also shown that the critical voltage in the system is affected by the flexoelectric effect, the geometric effect and radial weak anchoring effect on the cylindrical surfaces. A new type of director transition caused by the flexoelectric effect, the dielectric coupling effect and the radial weak anchoring effect is found.
Author: Agnes Buka Publisher: World Scientific ISBN: 1848167997 Category : Science Languages : en Pages : 299
Book Description
The book intends to give a state-of-the-art overview of flexoelectricity, a linear physical coupling between mechanical (orientational) deformations and electric polarization, which is specific to systems with orientational order, such as liquid crystals. Chapters written by experts in the field shed light on theoretical as well as experimental aspects of research carried out since the discovery of flexoelectricity. Besides a common macroscopic (continuum) description the microscopic theory of flexoelectricity is also addressed. Electro-optic effects due to or modified by flexoelectricity as well as various (direct and indirect) measurement methods are discussed. Special emphasis is given to the role of flexoelectricity in pattern-forming instabilities. While the main focus of the book lies in flexoelectricity in nematic liquid crystals, peculiarities of other mesophases (bent-core systems, cholesterics, and smectics) are also reviewed. Flexoelectricity has relevance to biological (living) systems and can also offer possibilities for technical applications. The basics of these two interdisciplinary fields are also summarized.
Author: L.M. Blinov Publisher: Springer Science & Business Media ISBN: 1461226929 Category : Science Languages : en Pages : 477
Book Description
Electrooptic effects provide the basis for much liquid-crystal display technology. This book, by two of the leaders in liquid-crystal research in Russia, presents a complete and accessible treatment of virtually all known phenomena occurring in liquid crystals under the influence of electric fields.
Author: Theo Rasing Publisher: Springer Science & Business Media ISBN: 3662101572 Category : Technology & Engineering Languages : en Pages : 301
Book Description
This book describes the state of the art of our understanding of liquid-crystal interfaces on a molecular level. The interactions of liquid crystal molecules with a surface play an essential role in the operation of liquid crystal displays (LCD's) and other LC devices that are based on the controllable anchoring of LC molecules on polymer coated surfaces. This book addresses the microscopic interaction between a macromolecule (liquid crystal, polymer) and a wall, using state of the art surface and interface-sensitive experimental techniques, such as Atomic Force Microscopy (AFM), Scanning Tunneling Microscopy (STM), Linear and Nonlinear Optical Microscopy and (Dynamic) Light Scattering (DLS). These experimental techniques were complemented with computer simulations and supra molecular chemistry methods to develop controllable polymeric surfaces.
Author: Yingfei Jiang Publisher: ISBN: Category : Liquid crystals Languages : en Pages : 0
Book Description
Liquid crystals are widely used in flat panel displays and smart windows. In flat panel display application, one way to improve the efficiency is to decrease the driving frequency when static images are displayed. As the driving frequency is decreased, the transmittance of the display may vary with time, a phenomenon known as flickering. We carried out both experimental and simulation studies to investigate the origins that cause the flickering problem. Our results show that flexoelectric effect and ions in the liquid crystal are the main factors responsible for the flickering. We quantitatively analyzed the flickering caused by the two factors. The ionic effect can be eliminated by using the fluorinated liquid crystals with high resistivity. The flexoelectric effect is attributed to the intrinsic flexoelectric coefficient of the liquid crystal and nonuniformity of the liquid crystal director configurations. We demonstrated that polymer stabilization can smooth the spatial variation of the liquid crystal orientation, while doping a liquid crystal dimer can reduce the flexoelectric coefficient of the liquid crystal. Using these methods we are able to reduce the flickering significantly. Radiant energy-flow control and privacy control are two important features for smart windows (or glass). Current smart window technologies can, however, only control one of them: radiant energy flow or privacy. Therefore, a dual-mode smart window is highly desirable. We developed a dual-mode switchable liquid-crystal window that can control both radiant energy flow and privacy. The switchable liquid-crystal window makes use of dielectric and flexoelectric effects. In the absence of an applied voltage, the window is clear and transparent, and radiant energy can flow through it and the scenery behind the window can be seen. When a low-frequency (50 Hz) voltage is applied, the window is switched to an optical scattering and absorbing state by a flexoelectric effect, and thus, privacy is protected. When a high-frequency (1 kHz) voltage is applied, the window is switched to an optical absorbing but nonscattering state through a dielectric effect, and thus, radiant energy flow is controlled. Smart windows can be categorized mainly into two types according to the operation principle: electrical switchable window and thermal switchable windows. In the electric switchable window, voltage must be applied to switch the window, which consumes energy and is not environmentally friendly. Therefore, a power-free smart window is highly demanded. We developed a thermal switchable smart window that is sensitive to ambient temperature. The window is based on a liquid crystal whose orientation imposed by an alignment layer varies with temperature. The liquid crystal layer is sandwiched between two parallel polarizers to make the window. At high temperature, the liquid crystal is aligned parallel to the cell substrate and rotates the polarization of the incident light after the first polarizer by 90o such that incident light is completely absorbed by the second polarizer, and the transmittance of the window is 0. When temperature is decreased, the liquid crystal is tilted toward the cell substrate normal and rotates the polarization of the incident light less so that some light can pass the second polarizer, and the transmittance of the window increases. When temperature is decreased below a critical value, the liquid crystal is aligned perpendicular to the cell substrate and does not rotate the polarization of the incident light such that all light passes the second polarizer, and the transmittance reaches a maximum.
Author: I. Jánossy Publisher: Springer Science & Business Media ISBN: 9401131805 Category : Science Languages : en Pages : 242
Book Description
In 1988 physicists and chemists commemorated the centenary of the discovery of the first liquid crystals. Fora long period after this discovery, although many significant results were found, liquid crystal research remained a marginal topic of condensed matter physics. The situation changed in the sixties. At that time the remarkable electro-optical properties of liquid crystals were recognized and found soon widespread application in numeric displays. From a more fundamental point of view, the interest in disordered systems. increased in general at the same time. Liquid crystals represented an important dass of such systems. Among others, phase transitions, hydrodynamics and topological defects occurring in them attracted considerable attention. The connection between the liquid-crystalline state and the structure of biological membranes stimulated a Iot of works also. In the present volume we discuss a relatively new and rapidly developing branch of the fi. eld, namely nonlinear optical effects in liquid crystals. Optical studies have always played a signifi. cant role in liquid crystal science. Research of optical nonlinearities in liquid crystals began at the end of the sixties. Since then it became a powerful tool in the investigation of symmetry properties, interfacial phenomena or dynamic behaviour. Furthermore, several new aspects of nonlinear processes were demonstrated and studied extensively in liquid crystals. The subject covered in this book is therefore of importance both for liquid crystal research and for nonlinear optics itself. The term "nonlinear optics" is used here in a broad sense.
Author: Kohki Takatoh Publisher: CRC Press ISBN: 1420023012 Category : Science Languages : en Pages : 280
Book Description
Alignment phenomena are characteristic of liquid crystalline materials, and understanding them is critically important in understanding the essential features and behavior of liquid crystals and the performance of Liquid Crystal Devices (LCDs). Furthermore, in LCD production lines, the alignment process is of practical importance. Alignment Technologies and Applications of Liquid Crystal Devices demonstrates both the fundamental and practical aspects of alignment phenomena in liquid crystals. The physical basis of alignment phenomena is first introduced in order to aid the understanding of the various physical phenomena observed in the interface between liquid crystalline materials and alignment layer surfaces. Methods for the characterization of surfaces, which induce the alignment phenomena, and of the alignment layer itself are introduced. These methods are useful for the research of liquid crystalline materials and devices in academic research as well as in industry. In the practical sections, the alignment methods used in the LCD production lines are introduced with various other trials for the alignment technologies. LCD performances are also discussed in relation to alignment phenomena. The authors have a wide range of experience in both academic research and in industry. This book will be of interest to researchers and engineers working in the LCD industry, and for physics and chemistry researchers studying liquid crystalline materials.
Author: Claudius Kischka Publisher: ISBN: Category : Languages : en Pages :
Book Description
Flexoelectricity in liquid crystals is thought to be due to a coupling between dielectric properties and shape anisotropy of the molecules and described by the fiexoelectric coefficients el and e3. Two experiments are needed to measure el and e3 and it is usual to measure the difference (el - e3) and the sum (el + e3) and then calculate el and e3· The first experiment to measure the difference (el - e3) uses a TN structure with an in-plane applied electric field. Due to the dielectric coupling, the director aligns with the electric field and due to the fiexoelectric effect, the director tilts out of plane. This tilt is measured optically using two laser beams at oblique incidence, e.g. 45°. Using a theoretical model the experimental data is fitted and the difference (el - e3) extracted. The second experiment to measure the sum (el + e3) uses a Pi cell. Applying an ac voltage the transmission through the device is a repeating oscillating signal which contains 1st and 2nd harmonics. The 1st harmonic corresponds to the fiexoelectric effect and the 2nd harmonic to the dielectric effect. Using a lock-in amplifier, the harmonics were measured and the sum (el + e3) extracted using a theoretical model to fit the experimental data. Unfortunately, the data proved the experiment to be unreliable and another method was developed, which uses a BAN cell. The third experiment uses simple pulses in a BAN cell and also measures the sum (el + e3). The big disadvantage of the BAN cell is an internal voltage, which is created by the homeotropic alignment layer and the fiexoelectric polarisation. The internal voltage has the same effect on the director profile as the fiexoelectric effect, which is a big problem in measuring fiexoelectricity. Using a material, which is non ionic and has no fiexoelectricity, the internal bias could be measured and taken into account. Applying short de pulses of opposite sign, the fiexoelectric effect can be observed by the optical response and can be measured. Using these experiments, a number of investigation are being carried out such as the correlation between fiexoelectricity and the molecular structure, ions, elastic properties, molecular orientation, dielectric anisotropy 6E, and order parameter S. The results showed that fiexoelectricity only depends on ions and dielectric properties which was very interesting and surprising at the same time.
Author: Wei Lee Publisher: Walter de Gruyter GmbH & Co KG ISBN: 3110583518 Category : Technology & Engineering Languages : en Pages : 738
Book Description
The work focuses on recent developments of the rapidly evolving field of Non-conventional Liquid Crystals. After a concise introduction it discusses the most promising research such as biosensing, elastomers, polymer films , photoresponsive properties and energy harvesting. Besides future applications it discusses as well potential frontiers in LC science and technology.
Author: Patricia Cladis Publisher: CRC Press ISBN: 9789056996499 Category : Science Languages : en Pages : 490
Book Description
During his distinguished scientific career, Alfred Saupe made important contributions to liquid crystal research, laying the groundwork on which much of the current knowledge and research in the physics of liquid crystals is based. This volume features papers presented by Prof. Saupe's colleagues, students and friends at a festschrift in honor of his 70th birthday. In addition, a selection of Prof. Saupe's articles are reprinted in the original German and in English translation, offering the reader a unique opportunity to see both the early work of this important scientist and widespread effect of that work on later discoveries in liquid crystal physics.
Author: 
Author: Agnes Buka
Author: L.M. Blinov
Author: Theo Rasing
Author: Yingfei Jiang
Author: I. Jánossy
Author: Kohki Takatoh
Author: Claudius Kischka
Author: Wei Lee
Author: Patricia Cladis