Light Scattering from Thin Smectic Liquid Crystal Films PDF Download
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Author: Mark Stuart Spector
Publisher:
ISBN:
Category :
Languages : en
Pages : 218
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Author: Mark Stuart Spector
Publisher:
ISBN:
Category :
Languages : en
Pages : 218
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Author: Sunil K. Sharma
Publisher:
ISBN:
Category : Fluctuations (Physics)
Languages : en
Pages : 157
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Smectic liquid crystalline films or membranes have been widely studied by using the hydrodynamic theory and dynamical scattering methods, but most studies have been confined to either frequency domain light scattering measurements above ~1GHz, which probe sound waves in a limit where damping is a weak effect, or by low frequency photon correlation spectroscopy, performed in the time domain below 10 MHz (i.e., for times) and usually designed to study overdamped fluctuations of the smectic layer orientation when inertia is negligible. The interesting crossover regime, where inertia, damping, and elastic forces all contribute significantly in the hydrodynamic description, has posed a long standing challenge to scattering experiments. In this dissertation we present an extension of the optical photon correlation spectroscopy (PCS) technique down to ~100 picosecond resolution that fully closes the historical gap between frequency and time domain scattering techniques. We study smectic films from which we can determine, for optical wavevectors 10^4-10^5/cm, both the propagation frequency and damping rate for undulatory motion of thin free standing smectic films (a few tens of molecular layers), as well as the relaxation rates associated with overdamped layer dynamics of bulk films (thousands of layers thick), by measuring the time correlation function of the intensity of light scattered from thermal motion of the film surfaces. We find that the standard hydrodynamic model for incompressible, isothermal smectic films provides a good overall framework for quantitative analysis of our correlation data in both under and overdamped regimes for films of common cyanobiphenyl liquid crystals in the SmA phase. In particular, the main elastic properties - the film surface tension and compression elastic constant - are found to be reasonably consistent with values obtained from other, more invasive techniques. However, there are significant aspects in which the standard model appears incomplete. First, in relatively thin films where the dominant scattering comes from nearly pure undulation modes of the film, the effective layer sliding viscosity is more than an order of magnitude less than values reported in bulk samples, typically measured between substrates. On the other hand, in a very thick film, we obtain a result, from purely overdamped dynamics, which basically agrees with quoted bulk values of the layer viscosity. Second, in thinner films, we detect an additional, overdamped mode not expected in the light scattering derived from the standard hydrodynamic theory. We propose that this mode is associated with consequences of a higher degree of order on the film surfaces. We have also carried out preliminary surface light scattering experiments on layer motion in thin smectic-C and hexatic-B films. The dynamical parameters obtained from fits to these data show only modest variations through the SmA-SmC and SmA-HexB transitions. The additional, overdamped mode is revealed to be clearly hydrodynamic (relaxation rate ~ square of wavevector) over the range probed.
Author: Elliot Golias
Publisher:
ISBN:
Category :
Languages : en
Pages :
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We describe the construction of a light scattering apparatus that is first used to conduct optical reflectivity measurements in thin smectic-A liquid crystal films to measure the thickness of films. Furthermore, we continue by conducting dynamic light scattering studies of films to obtain surface tension measurements for 8CB.
Author: Ivan Ivanov
Publisher: Taylor & Francis
ISBN: 1351408194
Category : Science
Languages : en
Pages : 1152
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Book Description
This comprehensive reference provided a systematic examination of both the theory and applications of thin liquid films - giving a critical review of major concepts and unresolved or controversial problems, as well as revealing experimental methods. It includes results previously unpublished. Combining the work of 20 leading researchers, Thin Liquid Films furnishes a fundamental overview of thermodynamics of thin liquid films. Generously illustrated with equations, tables and drawling and containing more than 2,200 citations to pertinent literature, this is an authoritative reference for physical, surface, and colloid chemists, biophysicists and physicists; chemical engineers and advanced graduate students in chemistry, chemical engineering, biophysics and physics.
Author: J. L. Birman
Publisher: Springer Science & Business Media
ISBN: 1461573505
Category : Science
Languages : en
Pages : 525
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Book Description
The Second USA-USSR Symposium on Light Scattering in Con densed Matter was held in New York City 21-25 May 1979. The present volume is the proceedings of that conference, and contains all manuscripts received prior to 1 August 1979, representing scientific contributions presented. A few manus cripts were not received, but for completeness the corresponding abstract is printed. No record was kept of the discussion, so that some of the flavor of the meeting is missing. This is par ticularly unfortunate in the case of some topics which were in a stage of rapid development and where the papers presented sti mulated much discussion - such as the sessions on spatial dis persion and resonance inelastic (Brillouin or Raman) scattering in crystals, enhanced Raman scattering from molecules on metal surfaces, and the onset of turbulence in fluids. The background and history of the US-USSR Seminar-Symposia on light scattering was given in the preface to the proceedings of the First Symposium held in Moscow May 1975, published as "Theory of Light Scattering in Condensed Matter" ed. B. Bendow, J. L. Birman, V. M. Agranovich (Plenum Press, N. Y. 1976). Strong scientific interest on both sides in continuing this series resulted in a plan for the second symposium to be held in New York in 1977. For a variety of reasons it was necessary to cancel the planned 1977 event, almost at the last minute.
Author: Shokir A. Pardaev
Publisher:
ISBN:
Category : Liquid crystals
Languages : en
Pages : 0
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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: Samuel Nash Sprunt
Publisher:
ISBN:
Category :
Languages : en
Pages : 524
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Author: Jan P F Lagerwall
Publisher: World Scientific
ISBN: 9814619272
Category : Science
Languages : en
Pages : 944
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'The overall book content is excellently coordinated to form a synchronised story, interesting to a broad scientific audience … The book summarises the present knowledge in the field, introduces fundamental concepts to the beginners, describes key measuring methods and presents several different typical demonstrative systems, some of them exhibiting an extraordinary rich spectrum of structures and superstructures. I am sure that with time the book will become an attractor to a broad audience (physicists, chemists, material scientists, engineers, etc.), ranging from students, beginners in the field to experienced researchers. To summarise, this is the book that I have been missing on my bookshelf.'Liquid Crystals TodayWhile liquid crystals are today widely known for their successful application in flat panel displays (LCDs), academic liquid crystal research is more and more targeting situations where these anisotropic fluids are put to completely different use, in varying contexts. A particularly strong focus is on colloidal liquid crystals, where particles, bubbles or drops are dispersed in a liquid crystal phase. The liquid crystal can act as a host phase, with the inclusions constituting foreign guests that disturb the local order in interesting ways, often resulting in large-scale positional arrangement and/or uniform alignment of the guests. But it may also be formed by solid particles themselves, if these are of nanoscale dimensions and of disc- or rod-shape, and if they are suspended in an isotropic liquid host at sufficient concentration.This book aims to cover both the modern research tracks, gathering pioneering researchers of the different subfields to give a concise overview of the basis as well as the prospects of their respective specialties. The scope spans from curiosity-driven fundamental scientific research to applied sciences. Over the course of the next decade, the former is likely to generate new tracks of the latter type, considering the exploratory and productive phase of this young research field.
Author: Robert Blinc
Publisher: World Scientific
ISBN: 9814506745
Category : Science
Languages : en
Pages : 682
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This book presents the basic physics of ferroelectric and antiferroelectric liquid crystals in a simple and transparent way. It treats both the basic and the applied aspects of ferroelectric and antiferroelectric liquid crystal research, starting from the discovery of ferroelectricity in liquid crystals in 1975 and ending with the resonant X-ray experiment in ferrielectric and antiferrielectric phases in 1998. Particular attention is paid to the optical properties, electrooptic effects, phase transitions and experimental methods used in liquid crystal research. Special chapters are devoted to dielectric spectroscopy, light scattering, NMR, STM and AFM in complex fluids. The more than 300 illustrations help to present the basic physics of liquid crystalline ferroelectrics and antiferroelectrics in a way that can be easily followed by students, engineers and scientists dealing with liquid crystal research.
Author: Lorraine Solomon
Publisher:
ISBN:
Category :
Languages : en
Pages : 170
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