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  • 1
    ISSN: 1436-2449
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Summary Poly(styrene-b-paramethylstyrene) block copolymer samples have been prepared in a mechanical press, cooled under pressure below the glass transition temperature and investigated by small angle neutron scattering. We observe a microphase separation transition from an orderd to a disorderd state with ascending pressure. The observed effect is not expected solely due to pressure, but the situation in the press is more complicated: (i) Ascending pressure leads to an increase of the glass transition temperature which slows down relaxations and hinders the evolution of thermodynamic equilibrium, (ii) the uniaxial movement of the piston leads to an uniaxial shear field and samples get oriented. An adiabatic heating during the pressing procedure has been found to be of minor influence. The situation is discussed with respect to common sample preparation conditions and processing.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 0025-116X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The discotic liquid-crystalline polymers poly[oxy(3,7,10,11-tetrapentoxy-2,6-triphenylenediyl)-oxycarbonyltetradecamethylenecarbonyl] (1), containing discotic mesogenic groups in the main chain and poly[methyl(3,6,7,10,11-pentapentoxy-2-triphenylenyloxyundecyl)siloxane] (2) with disc-like groups attached to the polymer chain by flexible spacers, are studied by X-ray diffraction, solid-state nuclear magnetic resonance, differential scanning calorimetry and dynamic mechanical measurements, in order to determine the dynamic and structural transitions. It is shown that low-temperature softening in both polymers is caused by the mobility of short aliphatic side chains attached to the discotic units. Once formed, the columnar mesomorphic structure is stable up to the temperature of isotropization. For the main-chain polymer, a third transition is observed in samples quenched from the melt. The transition is related to the mobility of the main chain in an amorphous structure, where the discotic units are not organized in columns.
    Additional Material: 11 Ill.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 96 (1992), S. 3183-3190 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Ordering effects of a side group liquid crystalline polymer PMA64 have been observed by the x-ray reflectivity technique. Thin films on float glass substrate are investigated as a function of temperature and film thickness. At 100 °C, a phase transition from a smectic-A to a nematic phase is observed. The layers of the smectic-A phase are oriented parallel to the surface giving rise to a Bragg peak which is coherently superimposed on Kiessig fringes. The Kiessig fringes are caused by interference of beams reflected at the polymer surface and the polymer–glass interface, while the Bragg peak originates from the electron density modulation perpendicular to the surface. As a function of film thickness, we observe a significant deviation of the integrated intensity of the Bragg peak as compared to the integrated intensity of a Bragg peak due to perfect periodic one-dimensional density modulations. A model which includes the influence of the interfaces as well as distortions of the first and second kind is used to describe this thickness dependence of smectic order in thin films of liquid crystalline polymers. The Bragg peak is lost at the smectic–nematic phase transition where we observe a significant roughening of the free surface. This effect is discussed with respect to molecular order.
    Type of Medium: Electronic Resource
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  • 4
    ISSN: 1022-1352
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Room temperature recast NafionGeneral formula: films, prepared under different humidities in the curing atmosphere, were characterized by small- and wide-angle X-ray scattering (SAXS and WAXS). SAXS reveals that the humidity influences the size of the ionic clusters in these polymer films. It was found that the number and size of ionic clusters increases with increasing relative humidity. WAXS indicates the presence of locally ordered regions of the backbone polymer. These results allow a qualitative understanding of the electrochemical behaviour of Nafion recast films cured at different humidities, as described in the literature.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
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  • 5
    ISSN: 1042-7147
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Stable monomolecular layers of a liquid-crystalline homopolymer bearing azobenzene chromophores in the mesogenic side groups could be prepared at the water-air interface by slow compression at room temperature. From the area per monomer unit of A0≈0.25 nm2 a structural model with tightly packed azobenzene groups oriented nearly parallel to the surface normal was deduced. After transfer to a solid support in a Y-type mode the obtained Langmuir-Blodgett-Kuhn (LBK) multilayer assemblies of varying thicknesses (from a double layer to a thick film of d = 238 nm, capable of guiding optical modes) were prepared and analyzed by X-ray reflection and optical evanescent wave techniques. A monolayer thickness of d0 = 2.52 nm, as well as the anisotropic index of refraction of these layers, could thus be evaluated.Photo-isomerization by UV-irradiation (at λ = (360±30)nm) was examined by UV-VIS absorption spectroscopy. X-ray reflectivity data of samples illuminated for 30 min showed a complete loss of the layered structure of the LBK samples. As a result strongly light-scattering films were obtained. Surface plasmon microscopy was used to demonstrate the usefulness of this photo-induced order-disorder transition for optical information storage.
    Additional Material: 10 Ill.
    Type of Medium: Electronic Resource
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  • 6
    ISSN: 1022-1352
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: A blend of polycaprolactone (PCL) and poly(2,2-dimethyltrimethylene carbonate) (PDTC) containing catalytic amounts of dibutyltin dimethoxide was prepared from solution. The blend was then subjected to melt-mixing at 200°C and samples were taken after different times. According to thermal analysis data, with the increase of reaction time a gradual loss of the crystallizability of the blend components is observed, and after 70 min at 200°C the system becomes completely amorphous. 13C NMR data suggest that the loss of crystallizability of the blend is accompanied by an abrupt decrease in PCL and PDTC sequence lengths reaching after 70 min at 200°C an average length of about two repeating units each. These effects are explained by transesterification reactions between the lactone and carbonate units.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
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  • 7
    ISSN: 1042-7147
    Keywords: Liquid crystalline polymers ; Surfaces ; Interfaces ; X-ray reflection ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: The order in thin films of a combined liquid crystalline polymer is studied by X-ray reflection. Films of thicknesses of less than 200 nm on float glass are investigated as a function of temperature. The polymer with mesogenic groups in the main and side-chains exhibits smectic and cholesteric mesophases. Measurements in the smectic phases show a Bragg peak and smectic layers are oriented parallel to the substrate. The sample is thus macroscopically ordered by the influence of substrate and free surface. The film surface is very smooth after spincoating; surface roughness is typically 0.8 nm. First annealing of samples leads to a significant roughening of the free surface; roughness increases to 2.1 nm. Order as a function of film thickness depends on the interaction of the polymer with the substrate and free surface. These interactions give rise to a typical correlation length of perturbations in smectic ordering.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    s.l. : American Chemical Society
    Langmuir 11 (1995), S. 3092-3096 
    ISSN: 1520-5827
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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