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Ordered Regions (ordered + regions)
Selected AbstractsPolyaniline-multiwalled carbon nanotube composites: Characterization by WAXS and TGAJOURNAL OF APPLIED POLYMER SCIENCE, Issue 1 2008T. Jeevananda Abstract Polyaniline/carboxylated multi-walled carbon nanotube (PAni/c-MWNT) nanocomposites have been synthesized by micellar aided emulsion polymerization with various c-MWNTs compositions, viz., 0.5, 1, 5, and 10 wt %. The microcrystalline parameters such as the nanocrystal size (,N,), lattice strain (g), interplanar distance (dhkl), width of the crystallite size distribution, surface weighted crystal size (Ds), and volume of the ordered regions were calculated from the X-ray data by using two mathematical models, namely the Exponential distribution and Reinhold distribution methods. The effects of heat ageing on the microcrystalline parameters of the PAni/c-MWNT nanocomposites were also studied and the results are correlated. The thermal stability and electrical resistivity of the PAni/c-MWNT nanocomposites were examined with thermogravimetric analysis (TGA) and a conventional two-probe method. The TGA data indicate that the thermal stability of the nanocomposites improved after the incorporation of c-MWNTs. The influence of temperature on the resistivity of the nanocomposites was also measured. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci 2008 [source] Structure and properties of poly(methyl methacrylate) particles prepared by a modified microemulsion polymerizationJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 3 2004Wan Jiang Abstract Nanoscale poly(methyl methacrylate) (PMMA) particles were prepared by modified microemulsion polymerization. Different from particles made by traditional microemulsion polymerization, the particles prepared by modified microemulsion polymerization were multichain systems. PMMA samples, whether prepared by the traditional procedure or the modified procedure, had glass-transition temperatures (Tg's) greater than 120 °C and were rich in syndiotactic content (55,61% rr). After the samples were dissolved in CHCl3, there were decreases in the Tg values for the polymers prepared by the traditional procedure and those prepared by the modified process. However, a more evident Tg decrease was observed in the former than in the latter; still, for both, Tg was greater than 120 °C. Polarizing optical microscopy and wide-angle X-ray diffraction indicated that some ordered regions formed in the particles prepared by modified microemulsion polymerization. The addition of a chain-transfer agent resulted in a decrease in both the syndiotacticity and Tg through decreasing polymer molecular weight. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 733,741, 2004 [source] Poly[1-(trimethylgermyl)-1-propyne] and poly[1-(trimethylsilyl)-1-propyne] with various geometries: Their synthesis and propertiesJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 14 2003V. S. Khotimsky Abstract The polymerization of 1,2-disubstituted acetylenes [1-(trimethylgermyl)-1-propyne and 1-(trimethylsilyl)-1-propyne] initiated by Nb- and Ta-based catalytic systems was studied within a wide temperature range (,10 to +80 °C) with solvents (cyclohexane, CCl4, toluene, anisol, and n -chlorobutane) with variable dielectric constants (2.023,7.390). Conditions ensuring the synthesis of poly[1-(trimethylsilyl)-1-propyne] (PTMSP) containing 20,80% cis units and poly[1-(trimethylgermyl)-1-propyne] (PTMGP) containing 3,65% cis units were determined. The PTMSP and PTMGP samples were amorphous, exhibited a two-phase structure characterized by the presence of less ordered regions and regions with an enhanced level of ordering, and differed in solubility. A correlation was found between the cis/trans ratio and the morphology, the geometrical density of PTMSP and PTMGP films, and the gas permeability of the polymers. The gas permeability and solubility behavior of PTMSP and PTMGP were examined in terms of the molecular characteristics of the polymer samples (the thermodynamic Kuhn segment and the Kerr electrooptic effect). It was demonstrated that the gas permeability, as well as the solubility of the polymers, was defined by their supramolecular ordering, which depended on the lengths of continuous sequences composed of units of analogous microstructures and on the flexibility of macrochains. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 2133,2155, 2003 [source] Modulation functions of incommensurately modulated Cr2P2O7 studied by the maximum entropy method (MEM)ACTA CRYSTALLOGRAPHICA SECTION B, Issue 2 2010Liang Li The maximum entropy method (MEM) has been used to determine electron density in superspace of incommensurately modulated chromium pyrophosphate from X-ray diffraction data measured by Palatinus et al. [(2006), Acta Cryst. B62, 556,566]. Chromium pyrophosphate, Cr2P2O7, contains ordered regions (83% of the volume) and regions with disorder. Analysis of the MEM density has allowed the determination of the displacive modulation functions within ordered regions. The disordered regions can be described as the alternate occupation of two conformations of the pyrophosphate group and two positions of the chromium atom, with occupational probabilities that depend continuously on the phase of modulation t. A structure model based on the interpretation of the MEM density provides a fit to the diffraction data of the same quality as the model given by Palatinus et al. (2006). The failure to find a model that better fits the data is attributed to the intrinsic inaccuracy of ,,0.01,Å for positions derived from the MEM and to the difficulties in constructing an appropriate model for the anharmonic ADPs and their modulation functions from electron densities. [source] Diffraction cartography: applying microbeams to macromolecular crystallography sample evaluation and data collectionACTA CRYSTALLOGRAPHICA SECTION D, Issue 8 2010Matthew W. Bowler Crystals of biological macromolecules often exhibit considerable inter-crystal and intra-crystal variation in diffraction quality. This requires the evaluation of many samples prior to data collection, a practice that is already widespread in macromolecular crystallography. As structural biologists move towards tackling ever more ambitious projects, new automated methods of sample evaluation will become crucial to the success of many projects, as will the availability of synchrotron-based facilities optimized for high-throughput evaluation of the diffraction characteristics of samples. Here, two examples of the types of advanced sample evaluation that will be required are presented: searching within a sample-containing loop for microcrystals using an X-ray beam of 5,µm diameter and selecting the most ordered regions of relatively large crystals using X-ray beams of 5,50,µm in diameter. A graphical user interface developed to assist with these screening methods is also presented. For the case in which the diffraction quality of a relatively large crystal is probed using a microbeam, the usefulness and implications of mapping diffraction-quality heterogeneity (diffraction cartography) are discussed. The implementation of these techniques in the context of planned upgrades to the ESRF's structural biology beamlines is also presented. [source] | |||||||||||||