Shear Rheology and Texture of a Thermotropic Liquid Crystalline Polymer PDF Download
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Author: Edwin Gyuhue Kim
Publisher:
ISBN:
Category :
Languages : en
Pages : 224
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Book Description
Author: Edwin Gyuhue Kim
Publisher:
ISBN:
Category :
Languages : en
Pages : 224
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Book Description
Author: Domenico Acierno
Publisher: Springer Science & Business Media
ISBN: 940091511X
Category : Technology & Engineering
Languages : en
Pages : 331
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Book Description
Liquid crystal polymers (LCPs) have many strange properties that may be utilized to advantage in the processing of products made from them and their blends with isotropic polymers. This volume (volume 2 in the series Polymer Liquid Crystals) deals with their strange flow behaviour and the models put forward to explain the phenomena that occur in such polymers and their blends. It has been known for some time that small ad ditions of a thermotropic LCP to isotropic polymers not only gives an improvement in the strength and stiffness of the blend but improves the processability of the blend over that of the isotropic polymer. In the case of lyotropic LCPs, it is possible to create a molecular composite in which the reinforcement of an isotropic polymer is achieved at a molecular level by the addition of the LCP in a common solvent. If the phenomena can be fully understood both the reinforcement and an increase in the proces sability of isotropic polymers could be optimized. This book is intended to illustrate the current theories associated with the flow of LCPs and their blends in the hope that such an optimization will be achieved by future research. Chapter 1 introduces the subject of LCPs and describes the ter minology used; Chapter 2 then discusses the more complex phenomena associated with these materials. In Chapter 3, the way in which these phe nomena may be modelled using hamiltonians is fully covered.
Author: David Wilson Giles
Publisher:
ISBN:
Category : Polyesters
Languages : en
Pages : 270
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Author: Giorgia Sgalari
Publisher:
ISBN:
Category :
Languages : en
Pages : 360
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Author: Ming Zhou
Publisher:
ISBN:
Category : Phase transformations (Statistical physics)
Languages : en
Pages : 0
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Book Description
"A combined main-chain/side chain liquid-crystalline polymer (MCSCLCP), PSHQ4-7CNCOOH, whose chemical structure of main-chain backbone is poly[(phenylsulfonyl)-p-phenylenene-1,4-tetramethylenebis(4-oxybenzoate)] and side-chain mesogen is 8-[(4-cyano-4'-phenyl)oxy]octanoic acid (7CNCOOH), was synthesized by condensation polymerization. For comparison, the corresponding main-chain liquid crystalline polymer PSHQ4 was also synthesized. The results of differential scanning calorimetry show that PSHQ4-7CNCOOH undergoes a glass transition at 85°C, and a nematic-to-isotropic (N-I) transition at 172°C; then it is a glassy nematic polymer. On the other hand, it has been found the PSHQ4 undergoes a glass transition at 130°C, an N-I transition at 260°C, and crystallization at temperatures between 130 and 260°C. Both the powder and fiber pattern of wide-angle X-ray diffraction indicate the presence of crystalline structure in PSHQ4. The images of polarized optical microscopy have shown that both PSHQ4-7CNCOOH and PSHQ4 have Schlieren texture. Banded structure appears in both the thermotropic state and lyotropic states of PSHQ4-7CNCOOH. The grafting of side-chain mesogenic groups (7CNCOOH) onto the main-chain backbone of PSHQ4 has significantly increased the bulkiness of PSHQ4-7CNCOOH, which apparently cannot pack well, giving rise to a glassy state. Also synthesized was PSHQ4-11CNCOOH having eleven methylene units in the side chain (11CNCOOH) grafted onto the main-chain backbone of PSHQ4. The transient shear flow, steady-state shear flow, oscillatory shear flow, and time evolution of dynamic moduli, upon cessation of shear flow, of PSHQ4-7CNCOOH and PSHQ4 in the thermotropic state were investigated. One of the objectives of this study was to investigate the role of side-chain mesogenic groups (7CNCOOH) influencing the rheological behaviors of PSHQ4-7CNCOOH in the thermotropic state. Thus, for comparison, the rheological behaviors of PSHQ4 were also investigated. Only positive values of first normal stress difference (N1) in steady-state shear flow were observed during the entire range of shear rates and temperatures investigated. Another objective of this study was to investigate the rheological behaviors of combined MCSCLCP in the lyotropic state. For this, lyotropic solutions of various concentration (22-70 wt%) of PSHQ4-7CNCOOH, and lyotropic solutions of 23 wt% and 30 wt% of smectic-forming PSHQ4-11CNCOOH dissolved in o-dichlorobenzene were prepared for rheological measurements. The major thrust was to investigate whether the lyotropic solutions of PSHQ4-7CNCOOH and PSHQ4-11CNCOOH might give rise to negative values of N1, and the effect of flexible spacer length of side-chain mesogenic groups (nCNCOOH) on the rheological behaviors of combined MCSCLCPs in the lyotropic state. Indeed, negative values of N1 were observed at intermediate shear rates for lyotropic solutions of PSHQ4-7CNCOOH having the concentration up to 27 wt%, and for 23 wt% lyotropic solutions of PSHQ4-11CNCOOH. Interestingly, negative values of N1 became positive as the measurement temperature decreased below a certain critical value. Thus, the sign of N1 is found to depend on both the concentration and temperature of the lyotropic solutions of PSHQ4-7CNCOOH and PSHQ4-11CNCOOH. Also, flow reversal of lyotropic solutions of PSHQ4-7CNCOOH was investigated. It has been found that both shear stress and first normal stress difference do not follow strain scaling after flow reversal."--Abstract
Author: Witold Brostow
Publisher: Springer Science & Business Media
ISBN: 1461557992
Category : Technology & Engineering
Languages : en
Pages : 534
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Book Description
may never overcome the effects of hysteresis and stress (see Chapters 6 and 12). The first sentence of the reference work, Handbook of Liquid Crystals, reads: The terms liquid crystals, crystalline liquid, mesophase, and mesomorphous state are used synonymously to describe a state of aggregation that exhibits a molecular order in a size range similar to that of a crystal but acts more or less as a viscous liquid: [2] In other words, molecules within a liquid crystalline phase possess some orientational order and lack positional order; furthermore, the shape of a liquid crystalline sample is determined by the vessel in which it is contained rather than by the orientational order of its aggregated molecules. The authors recognized the limitations and imprecision of this definition but, like others preceding them, could not devise a simple and generally applicable one that is better. Regardless, the terms 'liquid crystal' and 'mesophase' should not be used interchangeably. As mentioned above, all liquid crystals are mesophases, but all mesophases are not liquid crystals. Recent studies, employing elaborate and sophisticated analytical techniques, have permitted finer distinctions between classical crystals and mesophases. At the same time, they have made definitions like that from the Handbook of Liquid Crystals somewhat obsolete for reasons other than terminology. One part of the problem arises from the use of a combination of bulk properties (like flow) and microscopic properties (like molecular ordering) within the same definition.
Author: Tai-Shung Chung
Publisher: CRC Press
ISBN: 9781420012521
Category : Technology & Engineering
Languages : en
Pages : 392
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Book Description
Liquid crystal polymers are sometimes called super polymers--with good reason. Their wide range of exceptional properties and ease of processing make them design candidates for many demanding applications. This new book provides a thorough review of LCP technology with the emphasis on the chemistry, synthesis and characterization of the material in its many variants. Additional chapters cover processing and applications. From the Editor's Preface The field of thermotropic liquid crystalline polymers has grown substantially in the last two decades, with fundamental research, publications, commercial products, and patents. In the 1980's, Dr. Ralph Miano led my colleagues and me at Hoechst Celanese in commercializing the first thermotropic liquid crystalline polymers, based on Dr. Gordon Calundann's composition patents. Today, more than seven companies have produced thermotropic liquid crystalline polymer materials, with at least 50 variants available. Hence, it is timely to compile a comprehensive review on the nature of this type of material and the ongoing progress in this field.... The goals of this book are to summarize previous work, provide new insights into this class of polymers, and add to the understanding of the formation of liquid crystallinity. This book covers a wide range of topics and addresses different disciplines in the field. The chapters are arranged as a learning scheme for the professional, from basic science to applied engineering. The first few chapters summarize the syntheses of various polyester, polyester-amid, and polyimide liquid crystalline polymers. The science and origins of liquid crystal formation are revealed. Next, we introduce the characterizations of these materials by their different chemical and physical aspects. Because most commercially available thermotropic liquid crystalline polymers have been used in the form of composites, we have also incorporated a chapter on polymer blends, detailing blending mechanisms and resultant properties. Two chapters on thermosetting liquid crystalline polymers integrate them with other topics, because of their unique importance and their applications for microelectronics and packaging. The final chapter deals with the engineering and processing aspects of thermoplastic liquid crystalline polymers for a variety of applications.
Author: C. Carfagna
Publisher: Elsevier
ISBN: 1483287890
Category : Science
Languages : en
Pages : 278
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Book Description
The International Workshop on Liquid Crystalline Polymers (LCPs) held in June 1993 in Italy attracted many of the leading researchers in this area of polymer science. The meeting provided a forum for the exchange of research and ideas on current developments and future research and applications of liquid crystalline polymers. This volume consists of a selection of the best papers presented at the meeting covering synthesis and characterization, liquid crystalline thermosets, rheology, blends and composites containing LCPs and transport properties.
Author: A.A. Collyer
Publisher: Springer Science & Business Media
ISBN: 9781851665570
Category : Technology & Engineering
Languages : en
Pages : 494
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Author: Francesco Paolo La Mantia
Publisher: CRC Press
ISBN: 9780877629603
Category : Technology & Engineering
Languages : en
Pages : 196
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Book Description
In recent years, studies by both industry and academic researchers have opened the door to improving performance and reducing costs of these new materials. The particular structure and morphology of LCPs, as well as their peculiar rheological behavior, have stimulated researchers to develop new theoretical models and new characterization and processing techniques to more fully understand and utilize LCPs. Although the scientific literature is very rich in data on the synthetic techniques and on the relations between structure and phase behavior of these new polymers, the understanding of the rheological and processing aspects is still far from satisfactory-particularly in the case of LCP blends. In fact, although an appreciable number of patents and scientific papers have appeared describing the phase behavior, the rheology, and the mechanical properties of many of these polyblends, several aspects of the relations between processing and morphology, and between morphology and properties of these materials are still obscure or even controversial. Now, this new book, written by leading researchers, provides an up-to-date guide and reference to the processing, rheology and applications of pure LCPs and LCP blends. The book concisely reviews the synthetic procedures for the production of LCPs and discusses the rheological behavior and processing methods. Plus, the book examines present and future applications areas of LCPs and LCP blends.
