Molecular Orientation and Rheology of Liquid Crystalline Polymers Under Shear Flow PDF Download
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Author: Kwan Hongladarom
Publisher:
ISBN:
Category :
Languages : en
Pages :
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Author: Kwan Hongladarom
Publisher:
ISBN:
Category :
Languages : en
Pages :
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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: Victor Manuel Ugaz
Publisher:
ISBN:
Category :
Languages : en
Pages :
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Although liquid crystalline polymers (LCPs) offer considerable commercial potential for the production of lightweight materials possessing exceptional mechanical strength, the influence of flow on molecular orientation remains poorly understood in melt processable thermotropic systems. In this thesis, a combination of materials and experimental techniques are employed which allow structural measurements to be obtained under a variety of flow conditions in the melt. In situ x-ray scattering techniques are used as a structural probe to directly measure the influence of flow on molecular orientation, and to identify the presence of other structural arrangements which would otherwise be unobservable. First, we use this structural data to identify a link between the development of a hexagonal microstructure and the onset of region I shear thinning in lyotropic poly(gamma-benzyl-L-glutamate) in m-cresol. Next, two different model thermotropic systems are studied, a polyester and polyether respectively, which incorporate molecular architectures specifically designed to provide a stable nematic phase over a wide temperature range. We present measurements of molecular orientation in steady shear flow, during relaxation after cessation of shear flow, and in the transient periods during shear flow inception and reversal. Under certain combinations of temperature and shear rate, the polyether is found to display a dramatic transition in molecular alignment to a condition where orientation is favored parallel to the vorticity direction, rather than parallel to the flow direction as is typically observed. Both materials exhibit dynamic behavior in the nematic phase consistent with flow alignment, as opposed to director tumbling behavior which is often observed in lyotropic LCPs. This hypothesis is supported by comparison with an adaptation of the Ericksen transversely isotropic fluid model and the Larson-Doi model, both of which account for the polydomain texture characteristic of LCP materials. The Larson-Doi model yields better qualitative predictions of the evolution of orientation and stress during flow reversal, suggesting that distortional elasticity plays a significant role in this type of flow. However, some discrepancies remain between the model predictions and the experimentally observed behavior, suggesting that distortional elasticity may play a different role in the rheology of thermotropic LCPs than in lyotropes.
Author: Bruce Darrell Bedford
Publisher:
ISBN:
Category :
Languages : en
Pages :
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Author: Witold Brostow
Publisher: Springer Science & Business Media
ISBN: 9780412609008
Category : Technology & Engineering
Languages : en
Pages : 542
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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: A. M. Donald
Publisher: Cambridge University Press
ISBN: 9780521580014
Category : Science
Languages : en
Pages : 616
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Book Description
A 2006 edition explaining the underlying science and applications of liquid crystalline polymers.
Author: Edwin Gyuhue Kim
Publisher:
ISBN:
Category :
Languages : en
Pages : 224
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Author: R.S. Lenk
Publisher: Springer Science & Business Media
ISBN: 940109666X
Category : Science
Languages : en
Pages : 380
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Book Description
Everything flows, so rheology is a universal science. Even if we set aside claims of such width, there can be no doubt of its importance in polymers. It joins with chemistry in the polymerisation step but polymer engineering is supreme in all the succeeding steps. This is the area concerned with the fabrication of the polymer into articles or components, with their design to meet the needs in service, and with the long and short term performance of the article or component. This is a typical area of professional engineering activity, but one as yet without its proper complement of professional engineers. An understanding of polymer rheology is the key to effective design and material plus process selection, to efficient fabrication, and to satisfactory service, yet few engineers make adequate use of what is known and understood in polymer rheology. Its importance in the flow processes of fabrication is obvious. Less obvious, but equally important, are the rheological phenomena which determine the in-service performance. There is a gap between the polymer rheologist and the polymer engineer which is damaging to both parties and which contributes to a less than satisfactory use of polymers in our society. It is important that this gap be filled and this book makes an attempt to do so. It presents an outline of what is known in a concise and logical fashion. It does this starting from first principles and with the minimum use of complex mathematics.
Author: Chang Dae Han
Publisher:
ISBN:
Category : Technology & Engineering
Languages : en
Pages : 388
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Author: Vijay Kumar Thakur
Publisher: Springer
ISBN: 3319202707
Category : Technology & Engineering
Languages : en
Pages : 536
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Book Description
This book introduces various applications of liquid crystalline polymers as the emerging new class of high performance novel materials. The authors detail the advantageous properties of these LCs including optical anisotropic, transparency and easy control over structure. This interdisciplinary work includes valuable input from international projects with special focus on the use of liquid crystalline polymers and/or nanocomposites.
