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od 2020-09-20 |
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1. |
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NMR studies of restricted diffusion in lyotropic systems Tortuosity, 1/alpha, and surface-to-volume ratio, S/V, were determined in aqueous solutions of decylammonium, dodecylammonium and tetradecylammonium chlorides of various concentrations by measuring the apparent diffusion coefficient of water, D-app(Delta). This was found to be much smaller than in the bulk state. Such restricted diffusion is interpreted in terms of the Mitra model, where D(A) depends on diffusion time and is controlled primarily by S/V. The samples exhibit lamellar (L), hexagonal (H) and isotropic (1) liquid crystalline phases. We observed changes in S/V upon phase transition. In the lamellar and hexagonal phases, the system is ordered, resulting in relatively small S/V ratios, compared to the micellar-isotropic phase. We did not observe a dependence on the diffusion time, A, in the isotropic phase, because the duration of the experiment was not sufficiently short to observe the change from Dapp(A) to Den. We observed the effective diffusion coefficient of water, which directly probes the tortuosity of the system. The S/V ratios were obtained by fitting the Mitra model, using known values of the bulk water diffusion coefficients, and the assumption that D-app --> D-0 for Delta --> 0. S/V is correlated with the type of structure, increasing on transition to the isotropic phase and decreasing on transition to other phases. The change in tortuosity is small, but slightly larger for the isotropic phase.
(C) 2002 Elsevier Science (USA). |
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Solid State Nuclear Magnetic Resonance, 22(2-3), 394-408, (2002) |
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2. |
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Computer simulation of structure and microphase separation in model A-B-A triblock copolymers A set of computer simulations for three symmetric A-B-A triblock copolymer microarchitectures at varying temperatures is reported. By using the cooperative motion algorithm we obtain energy, specific heat, end-to-end distance, and bridging fraction as a function of the reduced temperature. The order-disorder transition temperatures are determined, an outline of a symmetric A-B-A triblock copolymer phase diagram is presented, and the visualization of different microstructures is given. A bicontinuous microstructure is reported at 67% fraction of A component.
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Physical Review E - Statistical, Nonlinear, and Soft Matter Physics, 66(3), 031804, (2002) |
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3. |
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Molecular dynamics of modified poly(p-phenylene sulfide) Solid state proton NMR dynamics of poly(p-phenylene sulfide) (PPS) is studied by using off-resonance technique. It is shown that this method is able to provide indirect information about the correlation times of the internal motions. The obtained results are in a good agreement with those reported in the literature for the same system but using other NMR methods.
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Polymer Processing Society PPS-18, 219-223, (2002) |
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(Pobrane: aktualizowanie) |
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4. |
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MAS NMR and FTIR spectra of framework aluminosilicates In the work, the results of Al-27 MAS NMR studies carried out for structures of different framework aluminosilicates are presented. The spectra of natural clinoptilolite and its sodium and hydrogen forms were measured. The zeolite spectra were obtained before and after incorporation of heavy metal cations (Pb2+, Cd2+, Ni2+ and Cr3+) into the zeolite structure. After decomposition of the spectra into component peaks differences caused by ion exchange were observed.
Additionally, NMR spectra of kalsilite (framework aluminosilicate, not belonging to zeolite group) and other zeolites (chabazite, heulandite and analcime) were measured.
Al-27 MAS NMR spectra of all the samples studied were compared with the FTIR spectra measured in the middle infrared region.
Based on the results obtained it has been proved that the interpretation of spectra obtained using these two different techniques can give some information concerning changes occurring in various framework aluminosilicate structures.
(C) 2002 Elsevier Science B.V. All rights reserved. |
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Journal of Molecular Structure, 614(1-3), 281-287, (2002) |
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5. |
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1H and 13C NMR studies of molecular dynamics in the biocopolymer of glycolide and epsilon-caprolactone Copolymers of glycolide and F-caprolactone were studied using differential scanning calorimetry and solid-state NMR. The variation of the T-1 relaxation time with temperature reflects local disorder and can be quantified in terms of the distribution of correlation times predicted by the Davidson-Cole model. T-1 relaxation is dominated by trans gauche lisomerisation, with an activation energy of 34-35 kJ mol(-1).
(C) 2002 Elsevier Science (USA). |
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Solid State Nuclear Magnetic Resonance, 22(1), 19-28, (2002) |
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6. |
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Influence of pyridinium chlorides on the physicochemical character, morphology and particle size distribution of natural chalk Studies on the surface modification of natural chalk from the Sobkow deposits (Poland) were conducted using cationic surfactants for the modification. Newly synthesized 1-alkoxymethyl-3-hydroxypyridinium chlorides were employed as the modifiers. The unmodified and the modified chalk were subjected to physicochemical evaluation. The surface modification was analysed by differential scanning calorimetry (DSC). Bulk density and the capacity to absorb water, dioctyl phthalate and paraffin oil were also evaluated. Studies on dispersion and particle morphology were conducted using scanning electron microscopy (SEM) and dynamic light scattering (DLS). The results obtained made it possible to conclude that chalks modified with pyridinium salts may find broad application in construction, plastics processing and many other branches of industry.
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Tenside Surfactants Detergents, 39(3), 33-39, (2002) |
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(Pobrane: aktualizowanie) |
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7. |
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High-resolution solid-state 13C NMR studies of poly[(R)-3-hydroxybutyric] acid Solid poly[(R)-3-hydroxybutyric] acid was examined by high-resolution C-13 MAS NMR, differential scanning calorimetry and infrared spectroscopy. The C-13 methyl group resonance consists of three components: the rigid amorphous phase, the crystalline phase and the mobile amorphous phase. Spectral deconvolution, using the Lorentz function, reveals the relative amounts as 62% crystalline and 38% amorphous at 333 K, and 42% crystalline, 40% pure amorphous and 18% beta-orthorhombic at 413 K. NMR indicates a large difference in molecular mobility between the crystalline and amorphous regions of the sample. Infrared spectroscopy shows that the stretching at 1725 cm(-1) (characteristic of the a-form) comes from the crystalline region, and the bands at 1744 cm(-1) (characteristic of the beta-form) and 1800 cm(-1) come from the amorphous region.
(C) 2002 Elsevier Science (USA). |
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Solid State Nuclear Magnetic Resonance, 21(3-4), 197-203, (2002) |
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8. |
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A comparison between the crystal and solution structures of Escherichia Coli asparaginase II The small angle X-ray scattering (SAXS) pattern of the homotetrameric asparaginase II from Escherichia coli was measured in solution in conditions resembling those in which its crystal form was obtained and compared with that calculated from the crystallographic model. The radius of gyration measured by SAYS is about 5% larger and the maximum dimension in the distance distribution function about 12% larger than the corresponding value calculated from the crystal structure. A comparison of the experimental and calculated distance distribution functions suggests that the overall quaternary structure in the crystal and in solution are similar but that the homotetramer is less compact in solution than in the crystal.
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Acta Biochimica Polonica, 49(2), 509-513, (2002) |
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9. |
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Molecular dynamics in polyethylene and ethylene-1-butene copolymer investigated by NMR methods H-1 and C-13 NMR spectra and H-1 spin-lattice relaxation times T1 and T1ρ have been employed to study the structure and molecular dynamics in polyethylene and ethylene-1-butene copolymer in the temperature range from 100 to 370 K. Results are interpreted in terms of alpha, beta and gamma-relaxation, as well as methyl group rotation. The activation energies for all motions were established. The incorporation of 1-butene into ethylene chain leads to an increase of mobility in amorphous and crystalline phases as well as appearance the C-13 resonance characteristic to the monoclinic structure in addition to the orthorhombic observed in both polymers. The crystallinity degree derived from T-1rho in studied polymers is close to that determined using DSC method.
(C) 2002 Elsevier Science Ltd. All rights reserved. |
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European Polymer Journal, 38(5), 961-969, (2002) |
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10. |
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Characterization of aged nitrile rubber elastomers by NMR spectroscopy and microimaging H-1 spin-lattice and spin-spin NMR relaxation times change markedly during the aging of nitrile rubber elastomers. NMR microimaging reveals heterogeneous changes in the aged samples. Aging proceeds mainly via additional chain cross-linking, and scission of the polymer chains does not appear to contribute. T-1 imaging shows that there is no spatial distribution of spin-lattice relaxation times.
© 2002 Elsevier Science Ltd. All rights reserved. |
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Polymer, 43(11), 3169-3172, (2002) |
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11. |
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Molecular dynamics study on homonuclear and heteronuclear chains of Lennard-Jones segments We report molecular dynamics (MD) simulation data for three simulated fluids: a homopolymer with 16 tangent Lennard-Jones (U) segments at the reduced temperature of 1.25, an equimolar binary homopolymer fluid with eight tangent U segments at 15 state points, and three corresponding copolymers with equimolar segment fraction and varying segment distribution at 15 state points. We find that the compressibility factors and energies do not change as the segment distribution varies in the copolymer example. The simulation data are compared with thermodynamic perturbation theory (TPT1) calculations, The TPT1 compressibility factors compare favorably with the MD data at high reduced temperatures but differ significantly at lower temperatures.
(C) 2002 Elsevier Science B.V. All rights reserved. |
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Fluid Phase Equilibria, 193(1-2), 179-189, (2002) |
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12. |
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Crystallization and preliminary crystallographic studies of five crystal forms of Escherichia Coli L-asparaginase II (Asp90Glu mutant) L-Asparaginase II from Escherichia coli with an Asp90Glu mutation in the active site has been crystallized in five polymorphic forms. Crystals of all polymorphs suitable for X-ray diffraction experiments were obtained by the vapour-diffusion method. Crystals of form I belong to the monoclinic system (space group C2), have unit-cell parameters a = 73.1, b = 133.1, c = 62.6 Angstrom, beta = 108.8 degrees and diffract to 2.27 degrees resolution. Three of the crystal forms are orthorhombic, with unit-cell parameters a = 225.4, b = 128.0, c = 62.6 Angstrom (form II, P2(1)2(1)2), a = 59.9, b = 71.2, c = 130.6 Angstrom (form III, primitive cell) and a = 73.8, b = 122.1, c = 124.2 Angstrom (form IV, P2(1)2(1)2(1) or P2(1)2(1)2); the crystals diffract to 2.33, 3.5 and 1.7 Angstrom, respectively. Polymorph V is trigonal, space group P3(1)21, with unit-cell parameters a = 123.1, c = 83.8 Angstrom; the crystals diffract to 2.65 Angstrom resolution.
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Acta Crystallographica Section D-Biological Crystallography, 58, 130-132, (2002) |
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13. |
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Facultatis Chemiae Universitatis Studiorum Mickiewiczianae Posnaniensis Annales II, 73-78, (2002) |
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14. |
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Facultatis Chemiae Universitatis Studiorum Mickiewiczianae Posnaniensis Annales II, 65-72, (2002) |
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15. |
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Adsorption of the quaternary ammonium salts on bentonite Sodium bentonite was subjected to the effect of two new homologue series of chlorides
(alcoxymethyl) dimethyloctyloamonium chlorides and 3-alcoxymethyl-1-octylimidazole chlorides
with the hydrophobic substituents of the same length. Morphology of the obtained modified bentonite
was studied under scanning electron microscope [SEM] and the degree of adsorption of the
ammonium salts was determined by two-phase titration. The results allowed an assessment of the
influence of the length of the hydrophobic substituents and the site of the quaternary nitrogen atom on
the adsorption of chlorides.
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Physicochemical Problems of Mineral Processing, 36(1), 299-306, (2002) |
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16. |
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Chemistry for Agriculture, 3, 131-134, (2002) |
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(Pobrane: aktualizowanie) |
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17. |
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Facultatis Chemiae Universitatis Studiorum Mickiewiczianae Posnaniensis Annales II, 155-160, (2002) |
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18. |
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Analytical study of beta-irradiated antibiotics in the solid state This paper reports results of the study on the influence of beta-irradiation on the physical and chemical properties of selected salts of beta-lactam antibiotics in solid state (sodium salt: ampicillin, azlocillin, benzylpenicillin, carbenicillin and piperacillin; potassium salt of benzylpenicillin, ampicillin anhydricum, ampicillin trihydricum, amoxicillin trihydricum and bacampicillin hydrochloride). The source of irradiation was a linear accelerator of electrons, and the irradiation effects were checked on the basis of the following: determination of mass, melting point and water contrent, and spectrophotometric (UV, IR) chromatographic and thermal (DTG, DSC) studies.
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Journal of Thermal Analysis and Calorimetry, 68(2), 423-436, (2002) |
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19. |
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Silane modified fillers for reinforcing polymers Some white natural fillers (kaolin and talc) and synthetic mineral ones (precipitated silica, sodium-aluminium silicate, zinc silicate, calcium silicate) together with waste materials (cement dusts and post-fluor silicas) were subjected to surface modification and characterised. Various types of silane coupling agents (amino-, mercapto-, methacryloxy- and ureidosilanes) were used for surface modification. The modified fillers were mixed with butadiene-styrene rubber, polyurethane and PVC. Good physico-mechanical properties were obtained for PVC containing talcs and kaolins modified with methacryloxy- and ureidosilanes. The strength of polyurethanes was increased most by modification of the fillers with mercapto- and aminosilanes.
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Polymers and Polymer Composites, 10(7), 541-552, (2002) |
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20. |
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NMR studies of the molecular dynamics of tert-butyl chloride confined in the mesoporous molecular sieve MCM-41 The molecular dynamics of tert-butyl chloride (TBC) confined in the molecular sieve MCM-41 were investigated by measuring NMR linewidths, lineshapes, and H-1 and H-2 spin lattice relaxation times. The temperatures of phase transitions of confined TBC are different from those in bulk. The behaviour of confined TBC can be explained assuming that the guest molecules form two kinds of molecular layers, one located at the pore surface and the other at the centre of the pore.
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Physical Chemistry Chemical Physics, 4(11), 2392-2397, (2002) |
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21. |
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Postępy Fizyki, 53(1), 54-55, (2002) |
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22. |
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Polietylen modyfikowany mleczanem wapnia W pracy przedstawiono metodę otrzymywania polietylenu modyfikowanego mleczanem wapnia oraz pochodną krzemoorganiczną mleczanu wapnia. Stosowano różne ilości napełniacza. Uzyskane tworzywa biorozpraszalne poddano badaniom mechanicznym.
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Mat. V Konferencji Naukowo-Technicznej "Polimery i Kompozyty Konstrukcyjne", 61-65, (2002) |
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(Pobrane: aktualizowanie) |
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Zaktualizowano: podstrony 2021-06-21 / bazę danych: 2024-11-02 by Webmaster: Zbigniew Fojud