Topological Defects Formed in Liquid Crystals Containing Solid Microspheres with Tailored Surface Properties PDF Download
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Author: Yuedong Gu
Publisher:
ISBN:
Category :
Languages : en
Pages : 246
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Book Description
Author: Yuedong Gu
Publisher:
ISBN:
Category :
Languages : en
Pages : 246
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Book Description
Author: Oleg D. Lavrentovich
Publisher: Springer Science & Business Media
ISBN: 9401005125
Category : Science
Languages : en
Pages : 356
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Book Description
Topological defects are the subject of intensive studies in many different branches of physics ranging from cosmology to liquid crystals and from elementary particles to colloids and biological systems. Liquid crystals are fascinating materials which present a great variety of these mathematical objects and can therefore be considered as an extremely useful laboratory for topological defects. This book is the first attempt to present together complementary approaches to the investigations of topological defects in liquid crystals using theory, experiments and computer simulations.
Author: Cheng Long
Publisher:
ISBN:
Category :
Languages : en
Pages : 0
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Book Description
Liquid crystal is a state of matter where constituents show orientational order, despite lack of translational order. For regular nematic liquid crystals, the ground state of orientational distribution of mesogens is described by a single axis, known as the director. Due to effects such as surface anchoring or chiral nature of added liquid crystal molecules, the uniformity in an orientational order field can be broken. The short-range spatial correlation persisting in the orientational order field, as well as topological defects enabled by the uniaxial symmetry manifested from the local orientational order of a nematic liquid crystal, often gives rise to abundant intriguing and sophisticated pattern formation in nematic liquid crystals. Studying the pattern formation and the topological defects in those orientational order fields is essential for understanding rheological and optical properties of nematic liquid crystals. Employing analytical and numerical tools, this dissertation explores the implications of elasticity theory which is commonly used to characterize the deformation of a uniform orientational order field, and the motion of different topological defects in nematic liquid crystals. In the conventional Oseen-Frank elasticity theory, a uniform ground state is protected by the elastic constants satisfying Ericksen inequalities. To examine the scope of the elasticity theory beyond the Ericksen inequalities, we revisit the Oseen-Frank elasticity theory for nematic liquid crystals from the perspective of a reformulated form and find a new set of necessary inequalities for Frank elastic constants to ensure the existence of stable solutions, which is weaker than the Ericksen inequalities. We therefore identify a regime where the Ericksen inequalities are violated but the system is still stable. Remarkably, lyotropic chromonic liquid crystals are in that regime. We investigate the nonuniform structure of the director field in that regime, show that it depends sensitively on system geometry, and discuss the implications for lyotropic chromonic liquid crystals. Applying the same reformulated elasticity theory, we prove that geometric frustration exists in cholesteric liquid crystals. We explicitly demonstrate influences of geometric frustration in two models. First, we consider a chiral liquid crystal confined in a long cylinder with free boundaries. When the radius of the tube is sufficiently small, the director field forms a double-twist configuration, which is the ideal local structure. However, when the radius becomes large enough, due to the geometric frustration, the director field transforms into either a cholesteric phase with single twist, or a set of double-twist regions separated by disclinations, depending on the ratio of disclination energy density to elastic energy density. Second, we study a cholesteric liquid crystal confined between two infinite parallel plates with free boundaries, and we find that geometric frustration induces buckled helical cholesteric structure close to the free boundaries, reminiscent of the Helfrich-Hurault instability. Inspired by the experimental observation that skyrmions in cholesteric liquid crystals can move like particles under applied electric fields, we propose a general theoretical methodology for studying the motion of localized topological objects in liquid crystals, based on collective coordinate method. In our method, the continuum field of a topological soliton is represented by a few macroscopic degrees of freedom, including the position of the excitation and the orientation of the background field, and the motion of the topological soliton is thus derived from the equations of motion for those macroscopic degrees of freedom. Using the coarse-grained method, we elucidate the mechanism of moving solitons and skyrmions in a toggling field. Finally, to understand disclinations, an important class of topological defects in liquid crystals, we build a simple nematic order tensor model for a disclination in a nematic liquid crystal clarifying an analytical relation between the properties of the tensor field close to a disclination and the rotation axis of the nematic orientation around the disclination, which turns out to be an important quantity for the behaviors of a disclination. Analogous to a dislocation in a solid, we find that a Peach-Koehler force can be induced to drive a disclination to move by applying an effective external stress, and that the force is closely related to the rotation axis of the nematic orientation. With the help of the Peach-Koehler force, we further develop a theoretical model for explaining the Frank- Read mechanism in nematic liquid crystals, where a pinned disclination can be multiplied under an effective external stress.
Author: Hideo Takezoe
Publisher: CRC Press
ISBN: 148224764X
Category : Science
Languages : en
Pages : 288
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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: Patricia Cladis
Publisher: CRC Press
ISBN: 9789056996499
Category : Science
Languages : en
Pages : 490
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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: Shenglan Chen
Publisher:
ISBN:
Category :
Languages : en
Pages : 64
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Book Description
Author: Oleg Lavrentovich
Publisher: Springer
ISBN: 9781402001697
Category : Science
Languages : en
Pages : 344
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Book Description
Topological defects are the subject of intensive studies in many different branches of physics ranging from cosmology to liquid crystals and from elementary particles to colloids and biological systems. Liquid crystals are fascinating materials which present a great variety of these mathematical objects and can therefore be considered as an extremely useful laboratory for topological defects. This book is the first attempt to present together complementary approaches to the investigations of topological defects in liquid crystals using theory, experiments and computer simulations.
Author: Bryce S. Murray
Publisher:
ISBN:
Category : Nematic liquid crystals
Languages : en
Pages : 162
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Book Description
I present a body of work regarding topological defects (TDs) in nematic liquid crystals. Defects having specific strengths were created in specified locations using atomic force microscope (AFM) lithography and the means by which the defects relieve the diverging strain energy near their cores was characterized as a function of cell depth and by probing with an electric field. I also work towards nanoparticle trapping in the scribed cores by doping a host liquid crystal with fluorescent nano-emitters. The technique of scribing an easy axis by AFM lithography was extended by writing Python scripts that produce densely-packed paths for the AFM tip to follow. I create several arrays of defects using this method in thin cells. I then probe the structure of the nematic director near each scribed core by applying a perpendicular electric field to a positive anisotropy liquid crystal. Of interest is the means by which the TDs relax the diverging energy at the defect cores. I show qualitatively that smaller cell depths promote defect splitting, whereas thicker cells promote defect escape, i.e., the director rotates out of the plane. The voltage profile of the transmitted intensity under crossed polarizers was examined, and shows that the liquid crystal can have a Freedericksz threshold voltage near a split defect, but not near an escaped defect. I then assemble thick cells, such that the disclination lines caused by the scribing run near the master surface and terminate on nearest-neighbors. I apply an in-plane field and show that the disclinations can deflect, interact, and can swap termination partners to effect a change in orientation of 90°. The local electric field required to make the disclinations interact was measured. Then I consider a technique whereby the diverging energy of the defect cores can be relaxed by suspending nano-emitters, specifically quantum and carbon dots, into the liquid crystal. We make progress towards trapping these nanoparticles in scribed defects. I include a description of some work done towards near-field optical scanning microscopy in thin nematic films. As a whole, this work serves to create TDs and explore several of their basic structural and electro-optic properties.
Author: Amine Missaoui
Publisher:
ISBN:
Category :
Languages : en
Pages :
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Author: Michael Walters
Publisher:
ISBN:
Category : Condensed matter
Languages : en
Pages : 94
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Book Description
Over the recent few years, condensed matter physics has keenly been testing out the compelling techniques from the toolbox of machine learning. Order parameters, phase transitions, and other thermodynamic quantities have been learned for different systems, including the Ising model and its variants, the XY model, many-fermion systems, and more. In the following work, we apply three different machine learning architectures towards the problem of identification of topological defects, specifically those seen in square-confined, two-dimensional liquid crystals, though the concepts and methods outlined are by no means restricted to this application. Simulated liquid crystals were modeled by off-lattice, hard, rod-like molecules via Monte Carlo. At high molecular density, geometric frustrations from the square confinement cause the nematic director field to develop an inhomogeneous pattern containing various topological defects as the main physical feature. We show machine learning can capture the correlation between defect positions and the nematic directors around them to classify these different topologies. With a feed-forward neural network, pre-sorting the off-lattice simulation data in a coarse-grained fashion is necessary for effective learning. We also bring to light the often overlooked reason for why pre-sorting was needed in this case. As a more generalizable approach, we show that a recurrent neural network, via feature correlation, can also learn the topologies without pre-sorting or any other input engineering. Finally, we investigate how unsupervised learning with principal component analysis can be used to accurately pinpoint the location and the type of winding disclinations in our two-dimensional liquid crystal model.
