scholarly journals The structural language of crystalline polymers

2021 ◽  
Author(s):  
Bernard Lotz
Keyword(s):  
Crystalline Polymers ◽  
Structural Language

Structure-property relations of liquid crystalline polymers

1987 ◽  
Vol 45 ◽  
pp. 460-463
Author(s):  
Linda C. Sawyer
Keyword(s):  
Solid State ◽  
Liquid Crystalline ◽  
Structural Model ◽  
Crystalline Polymer ◽  
Liquid Crystalline Polymers ◽  
Mechanical Anisotropy ◽  
Structure Property ◽  
Preparation Methods ◽  
Crystalline Polymers ◽  
Extended Chain

Recent liquid crystalline polymer (LCP) research has sought to define structure-property relationships of these complex new materials. The two major types of LCPs, thermotropic and lyotropic LCPs, both exhibit effects of process history on the microstructure frozen into the solid state. The high mechanical anisotropy of the molecules favors formation of complex structures. Microscopy has been used to develop an understanding of these microstructures and to describe them in a fundamental structural model. Preparation methods used include microtomy, etching, fracture and sonication for study by optical and electron microscopy techniques, which have been described for polymers. The model accounts for the macrostructures and microstructures observed in highly oriented fibers and films.Rod-like liquid crystalline polymers produce oriented materials because they have extended chain structures in the solid state. These polymers have found application as high modulus fibers and films with unique properties due to the formation of ordered solutions (lyotropic) or melts (thermotropic) which transform easily into highly oriented, extended chain structures in the solid state.

SEM/FESEM imaging of lamellar structures in melt extruded polyethylene films

1992 ◽  
Vol 50 (2) ◽  
pp. 1142-1143
Author(s):  
R.T. Chen ◽  
M.G. Jamieson ◽  
R. Callahan
Keyword(s):  
Imaging Techniques ◽  
Membrane Surface ◽  
High Stress ◽  
Extrusion Direction ◽  
Polymeric Membranes ◽  
Scanning Tunneling ◽  
Tunneling Microscopy ◽  
Crystalline Polymers ◽  
Lamellar Structures ◽  
Resolution Imaging

“Row lamellar” structures have previously been observed when highly crystalline polymers are melt-extruded and recrystallized under high stress. With annealing to perfect the stacked lamellar superstructure and subsequent stretching in the machine (extrusion) direction, slit-like micropores form between the stacked lamellae. This process has been adopted to produce polymeric membranes on a commercial scale with controlled microporous structures. In order to produce the desired pore morphology, row lamellar structures must be established in the membrane precursors, i.e., as-extruded and annealed polymer films or hollow fibers. Due to the lack of pronounced surface topography, the lamellar structures have typically been investigated by replica-TEM, an indirect and time consuming procedure. Recently, with the availability of high resolution imaging techniques such as scanning tunneling microscopy (STM) and field emission scanning electron microscopy (FESEM), the microporous structures on the membrane surface as well as lamellar structures in the precursors can be directly examined.The materials investigated are Celgard® polyethylene (PE) flat sheet membranes and their film precursors, both as-extruded and annealed, made at different extrusion rates (E.R.).

Factors affecting microstructural scale in liquid crystalline polymers

1990 ◽  
Vol 48 (4) ◽  
pp. 220-221
Author(s):  
Christine M. Dannels ◽  
Christopher Viney
Keyword(s):  
Liquid Crystalline ◽  
Liquid Crystalline Polymers ◽  
Factors Affecting ◽  
Crystalline Polymers ◽  
Thermal Expansion Coefficients ◽  
Low Thermal Expansion ◽  
Lower Viscosity ◽  
Fine Microstructure ◽  
Planar Orientation ◽  
Strength And Stiffness

Processing polymers from the liquid crystalline state offers several advantages compared to processing from conventional fluids. These include: better axial strength and stiffness in fibers, better planar orientation in films, lower viscosity during processing, low solidification shrinkage of injection moldings (thermotropic processing), and low thermal expansion coefficients. However, the compressive strength of the solid is disappointing. Previous efforts to improve this property have focussed on synthesizing stiffer molecules. The effect of microstructural scale has been overlooked, even though its relevance to the mechanical and physical properties of more traditional materials is well established. By analogy with the behavior of metals and ceramics, one would expect a fine microstructure (i..e. a high density of orientational defects) to be desirable.Also, because much microstructural detail in liquid crystalline polymers occurs on a scale close to the wavelength of light, light is scattered on passing through these materials.

Quantitative high-resolution electron microscopy (HREM) of defects in ordered polymers

1996 ◽  
Vol 54 ◽  
pp. 166-167
Author(s):  
Patricia M. Wilson ◽  
David C. Martin
Keyword(s):  
Electron Microscopy ◽  
Electron Beam ◽  
High Resolution ◽  
Liquid Crystalline ◽  
High Resolution Electron Microscopy ◽  
Polymer Materials ◽  
Scattered Electron ◽  
Crystalline Polymers ◽  
Resolution Electron ◽  
Beam Damage

Efforts in our laboratory and elsewhere have established the utility of low dose high resolution electron microscopy (HREM) for imaging the microstructure of crystalline and liquid crystalline polymers. In a number of polymer systems, direct imaging of the lattice spacings by HREM has provided information about the size, shape, and relative orientation of ordered domains in these materials. However, because of the extent of disorder typical in many polymer microstructures, and because of the sensitivity of most polymer materials to electron beam damage, there have been few studies where the contrast observed in HREM images has been analyzed in a quantitative fashion.Here, we discuss two instances where quantitative information about HREM images has been used to provide new insight about the organization of crystalline polymers in the solid-state. In the first, we study the distortion of the polymer lattice planes near the core of an edge dislocation and compare these results to theories of dislocations in anisotropic and liquid crystalline solids. In the second, we investigate the variations in HREM contrast near the edge of wedge-shaped samples. The polymer used in this study was the diacetylene DCHD, which is stable to electron beam damage (Jc = 20 C/cm2) and highly crystalline. The instrument used in this work was a JEOL 4000 EX HRTEM with a beam blanidng device. More recently, the 4000 EX has been installed with instrumentation for dynamically recording scattered electron beam currents.

Social Communication and Structural Language of Girls With High-Functioning Autism Spectrum Disorder

2020 ◽  
Vol 51 (4) ◽  
pp. 1139-1155
Author(s):  
Jenny M. Burton ◽  
Nancy A. Creaghead ◽  
Noah Silbert ◽  
Allison Breit-Smith ◽  
Amie W. Duncan ◽  
...  
Keyword(s):  
Autism Spectrum Disorder ◽  
Adaptive Behavior ◽  
Social Communication ◽  
High Functioning Autism ◽  
Autism Spectrum ◽  
Vineland Adaptive Behavior Scales ◽  
High Functioning ◽  
Expressive Communication ◽  
Vineland Adaptive Behavior ◽  
Structural Language

Purpose The purpose of this study was to characterize social communication and structural language of school-age girls with high-functioning autism spectrum disorder (HF-ASD) compared to a matched group of girls who are typically developing (TD). Method Participants were 37 girls between 7;5 and 15;2 (years;months)—18 HF-ASD and 19 TD. Children completed the Test of Pragmatic Language–Second Edition (TOPL-2) and Clinical Evaluation of Language Fundamentals–Fifth Edition. Parents completed the Children's Communication Checklist–2 United States Edition (CCC-2) and Receptive and Expressive Communication subdomains of the Vineland Adaptive Behavior Scales–Second Edition. Results In the area of social communication, girls with HF-ASD earned significantly lower scores and were more often classified as having an impairment on the TOPL-2 and the CCC-2. However, 28% and 33% earned average scores on the TOPL-2 and the CCC-2, respectively. In the area of structural language, no significant differences were found between groups on Clinical Evaluation of Language Fundamentals–Fifth Edition indexes. In contrast, girls with HF-ASD earned significantly lower scores and were more often classified as having an impairment on the Vineland Adaptive Behavior Scales–Second Edition. Sixty-one percent and 83% scored below average on the Receptive and Expressive Communication subdomains, respectively. Conclusions It has been argued that girls with HF-ASD, when compared to boys with HF-ASD, may have advantages for social communication and structural language that mask their impairments. However, when compared to girls who are TD, girls with HF-ASD demonstrated impaired social communication and structural language. Clinicians should include and carefully examine multiple sources of information when assessing girls with HF-ASD.

Linguistic Interactions: A Therapeutic Consideration for Adults With Aphasia

2008 ◽  
Vol 17 (3) ◽  
pp. 93-98
Author(s):  
Lynn E. Fox
Keyword(s):  
Clinical Outcomes ◽  
Social Contexts ◽  
Interaction Models ◽  
Social Communities ◽  
Wernicke's Aphasia ◽  
Communication Challenges ◽  
Therapeutic Consideration ◽  
Patterns Of Interaction ◽  
Structural Language

Abstract Linguistic interaction models suggest that interrelationships arise between structural language components and between structural and pragmatic components when language is used in social contexts. The linguist, David Crystal (1986, 1987), has proposed that these relationships are central, not peripheral, to achieving desired clinical outcomes. For individuals with severe communication challenges, erratic or unpredictable relationships between structural and pragmatic components can result in atypical patterns of interaction between them and members of their social communities, which may create a perception of disablement. This paper presents a case study of a woman with fluent, Wernicke's aphasia that illustrates how attention to patterns of linguistic interaction may enhance AAC intervention for adults with aphasia.

Polymer Chemistry

2004 ◽  
Keyword(s):  
Conducting Polymers ◽  
Liquid Crystalline ◽  
Polymer Chemistry ◽  
Chain Growth ◽  
Crystalline Polymers ◽  
Wide Range ◽  
Cyclic Oligomers ◽  
Step Growth

Polymer Chemistry: A Practical Approach in Chemistry has been designed for both chemists working in and new to the area of polymer synthesis. It contains detailed instructions for preparation of a wide-range of polymers by a wide variety of different techniques, and describes how this synthetic methodology can be applied to the development of new materials. It includes details of well-established techniques, e.g. chain-growth or step-growth processes together with more up-to-date examples using methods such as atom-transfer radical polymerization. Less well-known procedures are also included, e.g. electrochemical synthesis of conducting polymers and the preparation of liquid crystalline elastomers with highly ordered structures. Other topics covered include general polymerization methodology, controlled/"living" polymerization methods, the formation of cyclic oligomers during step-growth polymerization, the synthesis of conducting polymers based on heterocyclic compounds, dendrimers, the preparation of imprinted polymers and liquid crystalline polymers. The main bulk of the text is preceded by an introductory chapter detailing some of the techniques available to the scientist for the characterization of polymers, both in terms of their chemical composition and in terms of their properties as materials. The book is intended not only for the specialist in polymer chemistry, but also for the organic chemist with little experience who requires a practical introduction to the field.

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