In-Situ X-Ray Scattering Investigation of the Evolution of Molecular Orientation During Transient Flows of Model Thermotropic Liquid Crystalline Polymers PDF Download
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Author: Victor M. Ugaz
Publisher:
ISBN:
Category : Chemical engineering
Languages : en
Pages : 4
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Author: Victor M. Ugaz
Publisher:
ISBN:
Category : Chemical engineering
Languages : en
Pages : 4
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Author: Victor Manuel Ugaz
Publisher:
ISBN:
Category :
Languages : en
Pages :
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Book Description
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: David K. Cinader
Publisher:
ISBN:
Category :
Languages : en
Pages :
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Author:
Publisher:
ISBN:
Category : Dissertations, Academic
Languages : en
Pages : 886
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Author:
Publisher:
ISBN:
Category : Rheology
Languages : en
Pages : 616
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Author: Wilhelmus Hendrikus Jeu
Publisher: Oxford University Press
ISBN: 0198728662
Category : Science
Languages : en
Pages : 149
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Book Description
X-ray scattering is a well-established technique in materials science. The aim of this text is to explain basic principles and applications of x-ray scattering in a simple way using many practical examples followed by more elaborate case studies. It contains a separate chapter on the different types of order/disorder in soft matter that play such an important role in modern self-assembling systems. Finally the last chapter treats soft matter surfaces and thin film that are increasingly used in coatings and in many technological applications, such as liquid crystal displays and nanostructured block copolymer films
Author: Norbert Stribeck
Publisher: Springer Science & Business Media
ISBN: 3540698566
Category : Technology & Engineering
Languages : en
Pages : 251
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Book Description
This manual is a useful ready-reference guide to the analytical power of modern X-ray scattering in the field of soft matter. The author describes simple tools that can elucidate the mechanisms of structure evolution in the studied materials, and follows this up with a step-by-step guide to more advanced methods. Data analysis based on clear, unequivocal results is rendered simple and straightforward – with a stress on careful planning of experiments and adequate recording of all required data.
Author: Scott Guthrie McNamee
Publisher:
ISBN:
Category :
Languages : en
Pages : 314
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Author: B. I. Ostrovskii
Publisher: CRC Press
ISBN: 9783718649075
Category : Science
Languages : en
Pages : 76
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Book Description
Reviews recent studies of X-ray scattering phenomena in liquid crystals, in particular their relationship to phase-transition physics. Also explored are the main approximations which are used to obtain structural information from the scattering spectre of liquid crystals and to determine the short-range order in the molecule arrangement.
Author: K. H. J. Buschow
Publisher:
ISBN:
Category : Materials
Languages : en
Pages : 1160
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Book Description
Accompanyind CR-ROM conrtains The Encyclopedia of Materials Science and Technology on a web access disc.
