Structure-property Relations of a Liquid Crystalline Polymer and Attempts Toward an Oligomer Model PDF Download
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Author: Melissa Kay Thomas
Publisher:
ISBN:
Category : Liquid crystals
Languages : en
Pages : 70
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Author: Melissa Kay Thomas
Publisher:
ISBN:
Category : Liquid crystals
Languages : en
Pages : 70
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Book Description
Author: Derrick Resha Dean
Publisher:
ISBN:
Category :
Languages : en
Pages : 674
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Book Description
The crystal structure and morphology of a family of aromatic-aliphatic azomethine polyethers (where the aliphatic unit was composed of CH$sb2$ units ranging in length from n = 1, 4, 7, 8, 9 and 10) has been examined primarily by Electron microscopy(EM) and Electron diffraction(ED). Chain folded single crystals with lamellar thicknesses of 35-100A, in which the molecular axis is perpendicular to the substrate, have been grown by slow cooling thin films from the nematic state on a glycerin surface for n = 4, 8 and 10 with AZMEP-7 yielding disclination domains with isolated regions of chain folded lamellae. For as-polymerized AZMEP-10, the lamellae were found to be 35A thick The thinness of the lamellae and their tilt relative to the substrate and molecular axis suggests a regular, adjacent re-entry type folding every three repeat distances. AZMEP-1 was found to crystallize as striated films of near uniform thickness; in these samples, the molecular axes are parallel to the substrate, yielding fiber-type ED patterns. AZMEP-9 samples yielded a similar morphology, but no ED patterns were obtained. Our findings on samples crystallized as thin films has added to earlier findings by S. Kent and P. H. Geil, which gave the first conclusive evidence of chain folding in lcps. Claims were also made by them, and is supported by our findings, of the presence of chain folding in the nematic state. Sheared samples with lamellae ca. 250A and more or less perpendicular to the shear direction have been obtained for n = 1, 4, 7, 8, 9 and 10. Annealing below T$rmsb{k-m}$ has been shown to increase the lamellar thickness and overall order. ED from sheared, annealed samples surprisingly yield h01 single crystal patterns rather than the expected fiber patterns, which have rotational symmetry. This finding is unique, as far as we know, for sheared polymer samples. The h01 single crystal nature of these samples was verified by dark field EM. Lamellar single crystals (ca. 100A thick) have been grown by the constrained film melt polymerization technique for n = 4, 8 and 9, yielding single crystals suitable for ED. The ED data from these samples, in conjunction with data obtained from the sheared samples, has permitted characterization of the unit cells. We have examined creep above and below the nominal Tg in both the viscoelastic and viscoplastic load ranges for AS4/J1 uniaxial composites. Surprisingly, long term creep in tension does not appear to be a problem; it was found to be compensated by shrinkage due to physical aging, resulting in negative creep in the viscoelastic load range, and near zero creep in the viscoplastic load range. This fact makes the time-temperature superposition principle invalid for long term predictions; it actually overpredicts it in tension. The fact that physical aging occurs above Tg in subcrystalline polymers is attributed to the presence of a distributed Tg.
Author: Vijay Kumar Thakur
Publisher: Springer
ISBN: 3319228943
Category : Technology & Engineering
Languages : en
Pages : 627
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Book Description
This book introduces anisotropic innovations in liquid crystalline polymers as well as new nanocomposite materials and testing techniques. The authors detail the newest discoveries of material properties, material types and phases, and material characterization. This interdisciplinary work creates valuable links that strengthen the approach to the evolving field of liquid crystalline polymers/ materials.
Author: L. L. Chapoy
Publisher: Springer
ISBN: 9789400949355
Category : Science
Languages : en
Pages : 340
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Book Description
This volume contains an eclectic collection of 22 papers on liquid crystalline polymers presented at the Sixth Polymer Workshop, in the series sponsored by the European Science Foundation, entitled: 'Liquid Crystal Polymer Systems', in Gentofte, Denmark, 12-14 September 1983. Since a contribution to this volume was strictly voluntary, and in some cases represents a considerably expanded version of that which was presented, it is strictly speaking not correct to term this a 'proceedings'. A description of the aims and purposes of the European Science Foundation with respect to the polymer area has been presented in: Shell Polymers, Vol. 5, No.2, pp. 34-35, 1981. The papers given here represent a cross-section of current research interests in liquid crystalline polymers in the areas of theory, synthesis, characterization, structure-property relationships and applications. At least some of the current interest is motivated by attempts to practically exploit the novel properties of these materials in the developing tech nologies of high strength fibres and advanced materials for constructional purposes, but also for functional materials in the areas of information retrieval, electronics and opto-electronics applications. The editor wishes to thank all those involved for their courtesy and co-operation.
Author: Owen Torridon Howell
Publisher:
ISBN:
Category :
Languages : en
Pages :
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Author: A. Ciferri
Publisher: Wiley-VCH
ISBN:
Category : Psychology
Languages : en
Pages : 456
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Author:
Publisher:
ISBN:
Category :
Languages : en
Pages : 0
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Book Description
This project concerned the fundamental understanding of processing-structure and structure-property relations in block copolymer and liquid crystalline polymer systems. Key to our studies was the availability of model materials which afforded opportunities via new chemical compositions and physical properties. Transmission electron microscopy, low voltage high resolution scanning electron microscopy, light microscopy and atomic force microscopy as well as wide and small angle x-ray scattering were the principal characterization tools. We also employed a special roll cast process to form highly textured samples for investigation of their physical properties. Principal research accomplishments are grouped into 6 areas: influence of architecture on phase behavior; development of experimental techniques; microphase separation in block copolymers; large strain deformation of single crystal thermoplastic elastomers; morphology and dynamic interaction of defects in polymer liquid crystals; and technology transitions.
Author: Paola Anaid Gonzalez Garza
Publisher:
ISBN:
Category :
Languages : en
Pages : 92
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Book Description
Semi-crystalline polymers have shown increased crystalline order and size when confined in multilayered films by coextrusion1. The resulting large crystals lead to dramatic improvements in gas barrier properties. Ordered polymers whose characteristics are between that of the liquid phase and the crystalline phase are known as liquid crystalline polymers. The highly ordered mesogens in liquid crystalline polymers contribute to their exceptional bulk properties. In this research, side-chain liquid crystalline polymers were confined in multilayered films, made by either multilayer coextrusion or spin coating, with a non-liquid crystalline polymer in an attempt to improve the ordering of the liquid crystalline mesogens. The liquid crystalline behavior and morphology was studied to understand the correlation between the confinement size and the properties of the multilayer films. Commercial main chain liquid crystalline polymers and hydrogen bonded liquid crystalline polymers were also explored in this research for their use in multilayer coextrusion.
Author:
Publisher:
ISBN:
Category : Electrets
Languages : en
Pages : 1006
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Author: Stanley Rendon
Publisher:
ISBN:
Category :
Languages : en
Pages :
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Book Description
Thermotropic liquid crystalline polymers (TLCPs) offer considerable promise as high strength/lightweight engineering materials. Their excellent mechanical properties are derived from the spontaneous ordering of stiff polymer molecules in the melt state, which is ultimately translated into high molecular orientation in finished products. Understanding the effect of processing on molecular orientation, and specifically the role and mechanisms by which flow fields impact molecular orientation, is thus a prerequisite to rational design of processes that exploit and enhance the characteristics of TLCPs. The lack of fundamental knowledge to rationally anticipate structure development during processing of commercial main-chain TLCPs however, has significantly hindered the wide spread applicability of these materials. In light of the need for improved understanding of flow-orientation relationships in TLCPs, this thesis presents the first coordinated attempt to combine fundamental studies of orientation development in well-defined simple flows (simple shear) and complex processing flows (extrusion and injection molding) using in situ x-ray scattering methods, with structure and property investigations of injection molded plaques made from commercial TLCPs.
