Topological Defects in Nematic and Smectic Liquid Crystals PDF Download
Are you looking for read ebook online? Search for your book and save it on your Kindle device, PC, phones or tablets. Download Topological Defects in Nematic and Smectic Liquid Crystals PDF full book. Access full book title Topological Defects in Nematic and Smectic Liquid Crystals by Bryan Gin-ge Chen. Download full books in PDF and EPUB format.
Author: Bryan Gin-ge Chen
Publisher:
ISBN:
Category :
Languages : en
Pages : 121
Get Book Here
Book Description
Author: Bryan Gin-ge Chen
Publisher:
ISBN:
Category :
Languages : en
Pages : 121
Get Book Here
Book Description
Author: Oleg D. Lavrentovich
Publisher: Springer Science & Business Media
ISBN: 9401005125
Category : Science
Languages : en
Pages : 356
Get Book Here
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: Igor Muševič
Publisher: Springer
ISBN: 3319549162
Category : Science
Languages : en
Pages : 313
Get Book Here
Book Description
This book brings together the many concepts and discoveries in liquid crystal colloids contributed over the last twenty years and scattered across numerous articles and book chapters. It provides both a historical overview of the development of the field and a clear perspective on the future applications in photonics. The book covers all phenomena observed in liquid crystal colloids with an emphasis on experimental tools and applications of topology in condensed matter, as well as practical micro-photonics applications. It includes a number of spectacular manifestations of new topological phenomena not found or difficult to observe in other systems. Starting from the early works on nematic colloids, it explains the basics of topological defects in ordered media, charge and winding, and the elastic forces between colloidal particles in nematics. Following a detailed description of experimental methods, such as optical tweezing and particle tracking, the book eases the reader into the theoretical part, which deals with elastic deformation of nematic liquid crystals due to inclusions and surface alignment. This is discussed in the context of basic mean field Landau-de Gennes Q-tensor theory, with a brief explanation of the free-energy minimization numerical methods. There then follows an excursion into the topology of complex nematic colloidal structures, colloidal entanglement, knotting and linking. Nematic droplets, shells, handlebodies and chiral topological structures are addressed in separate chapters. The book concludes with an extensive chapter on the photonic properties of nematic dispersions, presenting the concept of integrated soft matter photonics and discussing the concepts of nematic and chiral nematic microlasers, surface-sensitive photonic devices and smectic microfibers. The text is complemented by a large bibliography, explanatory sketches and beautiful micrographs.
Author: Cheng Long
Publisher:
ISBN:
Category :
Languages : en
Pages : 0
Get Book Here
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: Shokir A. Pardaev
Publisher:
ISBN:
Category : Liquid crystals
Languages : en
Pages : 0
Get Book Here
Book Description
This research described in this dissertation comprises three experimental topics and includes the development of an appropriate theoretical framework to understand the various observations in each. In the first part, we present results from angle-resolved second-harmonic light scattering measurements on three different classes of thermotropic nematic liquid crystals: polar and non-polar rodlike compounds, and a bent-core compound. We analyze the data in terms of the "flexoelectric" polarization induced by distortions of the nematic director field around topological defects known as inversion walls, which are analogous to Neel walls in magnetic spin systems and which often exhibit a closed loop morphology in nematic systems.The second part of this dissertation explores the possible existence of a helical polarization field in the nematic twist-bend (NTB) phase of dimeric liquid crystals, utilizing a similar nonlinear light scattering approach. The NTB phase is characterized by a heliconical winding of the local molecular long axis (director) with a remarkably short, nanoscale pitch. According to theoretical conjecture, a helical electric polarization field accompanies this director modulation, but, due to the short pitch, presents a significant challenge for experimental detection. Our study focuses on topological defects, classified as parabolic focal conics, in two achiral, NTB-forming liquid crystals. These defects generate distortions of the polarization field on sufficiently long (micron) lengths to enable a confirmation of the existence of polar structure. We analyze our results with a coarse-grained free energy density that combines a Landau-deGennes expansion of the polarization field, the elastic energy of a nematic, and a bilinear coupling between the two.The last part of the dissertation focuses on the layer dynamics of thin, free-standing membranes of a smectic-A liquid crystal, with a particular consideration of the surface (interfacial) parameters that control these dynamics. We utilize photon correlation spectroscopy to probe the contributions of distinct under- and overdamped processes to the membrane motion. According to hydrodynamic theory, the frequency and damping rate of underdamped layer motion should scale with scattering vector in a manner controlled by the relative magnitude of a surface elastic constant, which is associated with gradients in surface tension, as well as by the average surface tension. In addition, the damping in very thin films is predicted to be quite sensitive to the presence of an atmosphere surrounding the film. A distinct, overdamped mode, observable in sufficiently thick films, is also predicted to couple to the layer motion. We present results on these dynamical modes and their dispersion and demonstrate their consistency with the hydrodynamic theory subject to appropriate surface boundary conditions.
Author: Shenglan Chen
Publisher:
ISBN:
Category :
Languages : en
Pages : 64
Get Book Here
Book Description
Author: Bryce S. Murray
Publisher:
ISBN:
Category : Nematic liquid crystals
Languages : en
Pages : 162
Get Book Here
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: Daniel A. Beller
Publisher:
ISBN:
Category :
Languages : en
Pages : 167
Get Book Here
Book Description
Author: Gregor Posnjak
Publisher: Springer
ISBN: 3319982613
Category : Science
Languages : en
Pages : 192
Get Book Here
Book Description
In this book Gregor Posnjak unravels the long-standing mystery of the internal director structure of chiral nematic droplets, which has been studied both experimentally and theoretically since the 1970s. To do so, he develops a new method for the reconstruction of director fields from a set of fluorescent confocal polarising microscopy images, which he augments with a simulated annealing algorithm. This allows the full reconstruction of 3D director fields, describing the ordering of the liquid crystal. The reconstruction procedure and its principles, which are applicable to other methods of studying vector fields, are explained in detail. The method is subsequently used to explore complex 3D structures in chiral nematic liquid crystal droplets with perpendicular surface anchoring. Twentyfour distinct states are identified and presented, including the layered structures of different symmetries and states with multiple topological point defects, separated by localized chiral structures. In closing, the book reports on the first observation of topological point defects with higher topological charges q = −2 and q = −3.
Author: Yuedong Gu
Publisher:
ISBN:
Category :
Languages : en
Pages : 246
Get Book Here
Book Description
