Structure and Rheology of Some Bent Core Liquid Crystals PDF Download
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Author: Christopher Allen Bailey
Publisher:
ISBN:
Category : Liquid crystals
Languages : en
Pages : 244
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Book Description
Liquid crystal phases composed of bent core molecules have been a fascinating topic in soft matter physics over the last decade. These materials which can form spontaneous polarizations (ferroelectricity) and chiral symmetry breaking with non-chiral molecules incited much interest in the scientific community. Since these early days, much research has been done on the characterization of these phases and their physical properties. In this work, we studied some of these properties by measuring the structural and viscous behavior using small amounts of material. The non-Newtonian flow characteristics of several bent core liquid crystals are characterized using a nanoliter viscometer. We show that many of these phases have viscoelastic behaviors which are fundamentally different from those observed in classical rod like liquid crystals. Finally, we studied the elasticity and dynamics of freestanding filaments which are stable structures in some bent core smectic phases. Characterization of their elasticity by resonance measurements and other techniques are in agreement with models designed to explain their microscopic smectic structures. We show that their viscosity, filament structure and stability, and microscopic structures can be understood by considering the role of steric interactions between molecules and the frustration thereof.
Author: Christopher Allen Bailey
Publisher:
ISBN:
Category : Liquid crystals
Languages : en
Pages : 244
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Book Description
Liquid crystal phases composed of bent core molecules have been a fascinating topic in soft matter physics over the last decade. These materials which can form spontaneous polarizations (ferroelectricity) and chiral symmetry breaking with non-chiral molecules incited much interest in the scientific community. Since these early days, much research has been done on the characterization of these phases and their physical properties. In this work, we studied some of these properties by measuring the structural and viscous behavior using small amounts of material. The non-Newtonian flow characteristics of several bent core liquid crystals are characterized using a nanoliter viscometer. We show that many of these phases have viscoelastic behaviors which are fundamentally different from those observed in classical rod like liquid crystals. Finally, we studied the elasticity and dynamics of freestanding filaments which are stable structures in some bent core smectic phases. Characterization of their elasticity by resonance measurements and other techniques are in agreement with models designed to explain their microscopic smectic structures. We show that their viscosity, filament structure and stability, and microscopic structures can be understood by considering the role of steric interactions between molecules and the frustration thereof.
Author: Hideo Takezoe
Publisher: CRC Press
ISBN: 1315355418
Category : Science
Languages : en
Pages : 290
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Book Description
Bent-Shaped Liquid Crystals: Structures and Physical Properties provides insight into the latest developments in the research on liquid crystals formed by bent-shaped mesogens. After a historical introduction, the expert authors discuss different kinds of mesophase structures formed by bent-shaped molecules. This book devotes the majority of its pages to physical properties such as polar switching, optics and non-linear optics, and behavior in restricted geometries. However, as chemistry is often highly relevant to the emergence of new phases, particularly with reflection symmetry breaking, it also involves a broad spectrum of interesting chemistry viewpoints.
Author: Seyyed Muhammad Salili
Publisher:
ISBN:
Category : Liquid crystals
Languages : en
Pages :
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Book Description
In this work, we describe dynamic behavior of free-standing bent-core liquid crystal filaments under dilative and axial compressive stresses in the B7 phase. We found that such filaments demonstrate very complex structures depending on the filament's temperature relative to the isotropic phase, initial filament thickness, and velocity at which the filament is pulled or compressed. We also present our experimental methods, results and analysis of the rupture and recoil properties of several bent-core liquid crystal filaments, anticipating that they may serve as a model system for complex biological fibers. After that, we systematically describe rheological measurements for dimeric liquid crystal compounds. We studied the shear-induced alignment properties, measured the viscoelastic properties as a function of temperature, shear rate, stress and frequency, and compared the results with the rheological properties of conventional chiral nematic and smectic phases. Then we present results of chiral nematic liquid crystals composed of flexible dimer molecules subject to large DC magnetic fields between 0 and 31T. We observe that these fields lead to selective reflection of light depending on temperature and magnetic field. The band of reflected wavelengths can be tuned from ultraviolet to beyond the IR-C band. A similar effect induced by electric fields has been presented previously, and was explained by a field-induced oblique-heliconical director deformation in accordance with early theoretical predictions. Finally, we report an unprecedented magnetic field-induced shifts of the isotropic-nematic phase transition temperature observed in liquid crystal dimers where two rigid linear mesogens are linked by flexible chains of either even- or odd-numbered hydrocarbon groups. This effect is explained in terms of quenching of the thermal fluctuations and decrease of the average bend angle of molecules in the odd-numbered dimers.
Author: Antal Jakli
Publisher: CRC Press
ISBN: 1420012207
Category : Science
Languages : en
Pages : 351
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Book Description
Smectic and lamellar liquid crystals are three-dimensional layered structures in which each layer behaves as a two-dimensional fluid. Because of their reduced dimensionality they have unique physical properties and challenging theoretical descriptions, and are the subject of much current research. One- and Two-Dimensional Fluids: Properties of Smec
Author: Shri Singh
Publisher: World Scientific
ISBN: 9814493457
Category : Science
Languages : en
Pages : 549
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Book Description
Liquid crystals are partially ordered systems without a rigid, long-range structure. The study of these materials covers a wide area: chemical structure, physical properties and technical applications. Due to their dual nature — anisotropic physical properties of solids and rheological behavior of liquids — and easy response to externally applied electric, magnetic, optical and surface fields liquid crystals are of greatest potential for scientific and technological applications. The subject has come of age and has achieved the status of being a very exciting interdisciplinary field of scientific and industrial research.This book is an outgrowth of the enormous advances made during the last three decades in both our understanding of liquid crystals and our ability to use them in applications. It presents a systematic, self-contained and up-to-date overview of the structure and properties of liquid crystals. It will be of great value to graduates and research workers in condensed matter physics, chemical physics, biology, materials science, chemical and electrical engineering, and technology from a materials science and physics viewpoint of liquid crystals.
Author: Hideo Takezoe
Publisher: CRC Press
ISBN: 9781482247596
Category : Science
Languages : en
Pages : 0
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Book Description
This book provides insight into the latest developments in the research on liquid crystals formed by bent-core mesogens. After a short historical introduction, the authors discuss different kinds of mesophase structures formed by bent-core molecules. A majority of this book is devoted to physical properties such as elasticity, optics and non-linear optics, and behavior in restricted geometries. As chemistry is often relevant to the emergence of new phases, particularly with chiral symmetry breaking, chemistry viewpoints are broadly involved in this book.
Author: Lev M. Blinov
Publisher: Springer Science & Business Media
ISBN: 9048188296
Category : Science
Languages : en
Pages : 448
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Book Description
This book by Lev M. Blinov is ideal to guide researchers from their very first encounter with liquid crystals to the level where they can perform independent experiments on liquid crystals with a thorough understanding of their behaviour also in relation to the theoretical framework. Liquid crystals can be found everywhere around us. They are used in virtually every display device, whether it is for domestic appliances of for specialized technological instruments. Their finely tunable optical properties make them suitable also for thermo-sensing and laser technologies. There are many monographs written by prominent scholars on the subject of liquid crystals. The majority of them presents the subject in great depth, sometimes focusing on a particular research aspect, and in general they require a significant level of prior knowledge. In contrast, this books aims at an audience of advanced undergraduate and graduate students in physics, chemistry and materials science. The book consists of three parts: the first part, on structure, starts from the fundamental principles underlying the structure of liquid crystals, their rich phase behaviour and the methods used to study them; the second part, on physical properties, emphasizes the influence of anisotropy on all aspects of liquid crystals behaviour; the third, focuses on electro-optics, the most important properties from the applications standpoint. This part covers only the main effects and illustrates the underlying principles in greater detail. Professor Lev M. Blinov has had a long carrier as an experimentalist. He made major contributions in the field of ferroelectric mesophases. In 1985 he received the USSR state prize for investigations of electro-optical effects in liquid crystals for spatial light modulators. In 1999 he was awarded the Frederiks medal of the Soviet Liquid Crystal Society and in 2000 he was honoured with the G. Gray silver medal of the British Liquid Crystal Society. He has held many visiting academic positions in universities and laboratories across Europe and in Japan.
Author: Ibon Alonso Villanueva
Publisher:
ISBN:
Category :
Languages : en
Pages : 162
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Book Description
Author: Heberth A. Diestra Cruz
Publisher:
ISBN:
Category : Anisotropy
Languages : en
Pages : 234
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Book Description
Author: Strahinja Stojadinovic
Publisher:
ISBN:
Category : Light
Languages : en
Pages : 219
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Book Description
Dynamical properties of the nematic and isotropic phase of several relatively new bent-core liquid crystals, as contrasted to conventional straight-core ("calamitic") liquid crystals, have been systematically studied by dynamic light scattering. Objective: Comparison of properties of bent-core nematics with straight-core nematics and search for a biaxial nematic phase due to the bent-core shape. Observations: Nematic phases are rather uncommon in bent-core compounds because nematic structure occurs only if the molecules can rotate relatively freely around their long axis, the condition apparently met in only a fraction of bent-core materials synthesized so far. The obtained results show that the elasticity to viscosity ratio for uniaxial bent-core nematics is typically two orders of magnitude lower than for straight-core nematics, due evidently to the large viscosity associated with optic axis distortions in the bent-core case. This result is independent of the normal mode of the director fluctuations probed. In one compound polarized light scattering data reveal fluctuations associated with the biaxial order parameter, occurring as a pretransitional effect on approach to the biaxial smectic-C phase. However, results on a homeotropically-aligned sample of another compound provide preliminary light scattering evidence for nematic biaxiality. Objective: To determine nature of isotropic to nematic phase transition and to measure dielectric fluctuations in the isotropic phase near the transition. Observations: The orientational order parameter fluctuations in the isotropic phase have been studied for the first time in bent-core compounds. Analogous to classic light scattering experiments performed on calamitic liquid crystals, fluctuations in nematic order in bent-core compounds exhibit a mean-field-like critical slowing down on approach to the isotropic-nematic transition from above. The fluctuations are intrinsically several orders of magnitude slower than for typical calamitics. In two related bent-core compounds, the transition is found to be weakly first-order, with the value of T NI -T* being ~3 times lower than the value typically obtained for calamitics. This reduction could be the effect of an enhanced density change at the I-N transition in the case of bent-core mesogens.
