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od 2020-09-20 |
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1. |
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Low-temperature ordering effects in diblock copolymer melts from lattice simulation A lattice simulation of a model diblock copolymer melt is presented. In a series of simulation experiments an 8-8 diblock melt is quenched from an athermal state to 47 lower temperatures. A set of simulation boxes, 30x32x30, 40x32x60, 50x32x30, and 60x32x30, is used in order to explore the size effects. Energy, specific heat, copolymer end-to-end distance, lamellar spacing, and the degree of interfacial ordering are reported. For all sizes considered, the low-temperature interfacial ordering is noticeable.
(C) 2004 American Institute of Physics. |
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Journal of Chemical Physics, 121(23), 12044-12049, (2004) |
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2. |
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Structural relaxation and morphology of the rubber-urethane composites The supermolecular structures and structural relaxation of the waste rubber-urethane composites are discussed on the basis of results of calorimetric measurements and mechanical spectroscopy. The results give a broader understanding of the relationship between processing history and morphology in the resultant engineering products. The effect of different kinds of urethane prepolymer on the thermomechanical properties of commercial composite products is presented. The idea of reaction between rubber granulate and urethane prepolymer is under consideration. The shear and tensile modes were applied to better explore relaxations that occur in rubber grains and in an interphase area created by the urethane agents. The rubber waste management problem was taken into account also.
(C) 2004 Wiley Periodicals, Inc. |
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Journal of Applied Polymer Science, 94(3), 1186-1193, (2004) |
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3. |
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Two polymorphs of a covalent complex between papain and a diazomethylketone inhibitor The three-dimensional structure of two polymorphs of a ZLFG-CH2-papain covalent complex has been determined by X-ray crystallography. The structures indicate that: (i) the methylene carbon atom of the inhibitor is covalently bound to the S atom of Cys25 of papain; (ii) the hydrophobic S2 pocket formed by Pro68, Val133, Val157, and Asp158 is occupied by the inhibitor's phenylalanyl P2 side chain; (iii) extensive hydrogen bonding and hydrophobic interactions are responsible for the interaction of the inhibitor with the enzyme. Comparison with similar structures suggests that in covalent complexes preservation of main chain-main chain interactions between the enzyme and the inhibitor may have higher priority than the P-S interactions
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Journal of Peptide Research, 64, 141-150, (2004) |
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4. |
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Layer-by-layer assembled composites from multiwall carbon nanotubes with different morphologies We report formation of polyelectrolyte/multiwall carbon nanotube (MWNT) multilayers; by the layer-by-layer assembly technique. Both "hollow" and "bamboo" type MWNTs were employed. Scanning electron and atomic force microscopy indicate high structural homogeneity of the prepared composites. Ellipsometry and the absorbance spectroscopy confirm sequential adsorption of oppositely charged nanotubes and the polyelectrolyte resulting in uniform growth of the polyelectrolyte/MWNT films. Measurements of the mechanical properties show that these are strong composite hybrid films with mechanical properties exceeding many carbon nanotube composites made by mixing, or in-situ polymerization. Bamboo-type carbon nanotube composites display ultimate tensile strength of 150 ± 35 MPa and Young modulus of 4.5 ± -0.8 GPa as compared to 110 ± 25 MPa and 2 ± 0.5 GPa in composites made from common hollow MWNTs. This indicates that the morphology of the fibers can substantially improve matrix connectivity on the material mitigating "telescopic effect" in MWNTs. The films made from bamboo-type MWNTs approach in strength recently reported layer-by layer composite films from single wall carbon nanotubes, while being substantially less expensive. These results confirm the potential of the layering method for the manufacturing of composites with high load of strong filler and importance of uniform distribution and good interconnectivity between carbon nanotubes and the polymer matrix.
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Nano Letters, 4(10), 1889-1895, (2004) |
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5. |
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SAS characterization of organic film deposited on porous silicas The small angle scattering methods can be used to investigate the density scattering profile at phase boundaries; in the following paper SAXS method was used for the characterization of organic film deposited on porous inorganic carriers. The existence of organic film on the surface of the porous carrier causes the changed in scattering; negative and positive deviations from Porod’s law can occurred. Significant differences in Porod’s plot of hydrated and dehydrated ZrO2 samples coated by bromododecanol were observed. These differences suggest considerable differences in alcohol molecules orientation on the two kinds of surface and confirm that the SAXS method can be used in determination of the structure of organic phase deposited on the porous surface.
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Applied Crystallography, 351-354, (2004) |
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6. |
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Collective and local molecular dynamics in the lyotropic mesophases of decylammonium chloride: 1H and 2H NMR study The collective and individual dynamics of decylammonium chloride (DACl) molecules in water environment were investigated as a function of surfactant concentration and temperature. In the presence of water the DACl forms a variety of self-assembled structures, ranging from isotropic micellar systems to lyotropic liquid crystalline phases of hexagonal, nematic, and lamellar types. In order to characterize the complex molecular dynamics that occur in the DACl-water system, we applied H-1 and H-2 NMR techniques that cover the whole frequency range between 1 kHz and 30 MHz. The slow molecular dynamics were studied by H-1 NMR fast-field-cycling T-1 measurements and pulse-frequency dependence of H-2 NMR transverse relaxation time, performed by means of the Carr-Purcell-Meiboom-Gill sequence. We detected a well-expressed contribution of order director fluctuations, i.e., layer undulations, with characteristic omega(L)(-1) frequency dependence of T-1(-1) in the lamellar phase. Its presence indicates a relatively weak impact of interactions between neighboring DACl layers. The frequency dependence of proton T-1(-1) in the hexagonal phase exhibits a different type of frequency dispersion, T(1)(-1)similar toomega(L)(-1.32). The increase in the exponent is explained with the quasi-one-dimensional character of fluctuations in elongated cylinders. Further, the T-1 and T-2 relaxation times of deuterons selectively attached to the C2 and C7 segments of the hydrocarbon chains of DACl were measured at a Larmor frequency of 30.7 MHz, providing quantitative information about local molecular dynamics.
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Physical Review E - Statistical, Nonlinear and Soft Matter Physics, 70, 031701, (2004) |
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7. |
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1H NMR study of hydrogen bonding and molecular dynamics of 5CB confined to molecular sieves It has been found that the main mechanism of H-1 protons spin-lattice relaxation of bulk 5CB at 200 MHz is its intramolecular motion, namely, the reorientation of CH2 and CH3 groups of its alkyl chain. Activation parameters of such motions have been estimated.
Drastic decrease in proton spin-lattice relaxation times at the nematic-to-isotropic phase transition can be explained by the activation of molecular translational diffusion and reorientations around long and short molecular axes of bulk 5CB.
Our NMR analysis revealed the slowing-down of molecular dynamics of confined 5CB molecules and their fragments. This can be explained by the interaction of some part of 5CB molecules with the surface active Si(Al)-OH centers of MCM matrix via hydrogen bonds of Si(Al)-(OHN)-N-... drop C-type.
(C) 2004 Elsevier B.V. All rights reserved. |
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Journal of Molecular Structure, 700(1-3), 183-189, (2004) |
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8. |
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Preparation and structural study of the composites of polyethylene with modified bentonite The paper reports a study on obtaining and characterisation of organophilised bentonite. Modification of the bentonite studied has been confirmed by SEM, XRD and NMR results. The organoplilised filler has been used for preparation on nanocomposites based on polyethylene or polyethylene modified with vinyltriethoxysilane and lactic acid. The best mechanical parameters have been obtained for the composites on the basis of the modified polyethylene containing 4% of organophilised bentonite and 50% of lactic acid.
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Mat. VI Konferencji Naukowo-Technicznej "Polimery i Kompozyty Konstrukcyjne", 69-74, (2004) |
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(Pobrane: 2021-01-08) |
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9. |
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Direct comparison of the crystal and solution structure of xylanase from Trichoderma Longibrachiatum The small angle X-ray scattering (SAXS) data of xylanase XYNII (endo-1.4-beta-xylan xylanohydrolase EC 3.2.1.8) From Trichoderma logibrachiatum, an enzyme catalysing the reaction of accidental hydrolysis of beta-1.4-D-xylosidic linkages of xylan, were recorded for protein solution using synchrotron radiation. The experimental data were compared with those of theoretical scattering calulated on the basis of the known crystal structure. The radius of gyration measured by SAXS (RG=1.7 nm) was about 3.5% larger and the maximum dimension in the distance distribution function about 5% larger than the corresponding values calculated oil the basis of the crystal structure.
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Protein and Peptide Letters, 11(4), 301-306, (2004) |
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10. |
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1H NMR spectra of 5CB liquid crystal and 5CB-MCM heterogeneous system It is shown that, in the 1H NMR spectra of 5CB, the splitting of proton bands is the result of the dipole-dipole interaction. Using the value of the splitting of the 1H bands, we determined the order parameters S for some fragments of 5CB molecules in the nematic phase. It is found that the values of S for the biphenyl core are twice greater than that for alkyl radical, which is the evidence for different dynamics of these structure fragments. From the analysis of the form of bands in the 1H spectra in the hetereogeneous system 5CB-MCM, we showed that, in the temperature range of the existence of the nematic and crystal phases of bulk 5CB, there is no ordering of these molecules in the channels of MCM. This is caused by the appearance of defects in the liquid crystal ordering due to the interaction of some part of the LC molecules with the active centers of the surface of MCM channels.
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Proceedings of SPIE - XVI International Conference on Spectroscopy of Molecules and Crystals, 5507, (2004) |
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11. |
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Length scales which perturb chain packing in amorphous polymers Direct spectroscopic probes of individual chain conformation and free volume are used to
measure the increasing perturbation in the local glass-transition temperature of one polymer chain with
decreasing length scale of mixing in binary polyolefin blends. Solid-state 2H and 129Xe NMR experiments
reveal a compositional miscibility window in side-chain concentration for polyisobutylene (PIB)/poly-
(ethylene-co-butene) (PEB) blends. A combination of pulsed-field gradient and chemical shift data for
xenon gas absorbed in these polymer blends indicates that the presence of polymer chains within a radius
of ~35 nm of a different chain structure will perturb the intermolecular packing contribution to the total
conformational energy of that chain, thereby changing its Tg
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Macromolecules, 37(12), 4573-4579, (2004) |
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12. |
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Dental Forum, 30(1), 177-185, (2004) |
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(Pobrane: aktualizowanie) |
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13. |
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Ferroelectric order in highly disordered molecular-ionic crystals The ordering of the anionic sublattice at the coexisting high orientational disorder of the cationic sublattice
produces spontaneous polarization in imidazolium tetrafluoroborate [C3N2H5]+ [BF4]-. This ferroelectric
crystal exhibits the Curie point at 297.0 K and undergoes two other polymorphic phase transitions at 213.6 and 187.8 K. In spite of its pentagonal ring the dynamically disordered polar cation is localized at a special position on the threefold axis of the highly symmetrical rhombohedral unit cell. Thus it does not contribute immediately to the spontaneous polarization which originates predominantly from the behavior of the distorted tetrahedral
fluoroborate anion.
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Physical Review B - Condensed Matter and Materials Physics, 69(13), 132102, (2004) |
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14. |
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Radial distribution fuctions and compressibility factors for binary mixture of hard spheres from molecular dynamics simulation Molecular dynamics simulation of binary mixtures of hard spheres with large size ratio is reported. Radial distribution functions, their contact values and the compressibility factors are recorded at three state points. A reasonably good agreement with theory and Monte Carlo simulations is shown.
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Computational Methods in Science and Technology, 10(2), 161-167, (2004) |
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15. |
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Low-temperature extra ordering effects in symmetric block copolymers from lattice monte carlo simulation Lattice computer simulations of block copolymer melts are reported. Low-temperature
lamellar ordering conjecture is presented and its justification is provided. In addition to reviewing the
previous data we present a new evidence for the extra ordering effects by recording the mean squared
rotational angles as a function of the reduced temperature.
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Computational Methods in Science and Technology, 10(2), 219-228, (2004) |
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16. |
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Relationship between filler loading and morphology of the interphase in polyethylene-chalk composites Mineral fillers such as kaolin or chalk have been commonly used in the polymer industry as additives to improve polymer mechanical properties and, at the same time, reduce the cost of raw materials. The problem is that the hydrophilic surface of the filler hinders its introduction into the polymer matrix. The paper reports a study of low density polyethylene (LDPE) composites with a natural chalk content of up to 40% wt. The morphology of the filler molecules and the microstructure of the composites were determined by scanning electron microscopy (SEM). The distribution of the filler molecules was estimated by light scattering. The mean diameter of the filler particles was 926.3 nm and their polydispersity was 0.101. The thermal and mechanical properties of the composites were characterised by differential scanning calorimetry (DSC) and dynamic mechanical thermal analysis (DMTA). The enthalpy of melting, DeltaH(m)*, decreased by about 8% when the amount of filler was 10 wt% in the sample (PE10). However, no difference was recorded between the DeltaH(m) value of the sample with 40 wt% content of filler (PE40), and the value for PE10. In LDPE composites with 40% of chalk,the free space in the interphase is reduced, slightly increasing the chain mobility in comparison with that in the composite with 10% of chalk.
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Polymers and Polymer Composites, 12(5), 409-416, (2004) |
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17. |
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Structure and crystallization behaviour of poly(epsilon-caprolactone)/clay intercalated nanocomposites Nanocomposites of poly(epsilon-caprolactone)/M-HTAB were obtained by polymerization of caprolactone with various amounts (10, 30, 50 and 64 weight ratio) of montmorillonite organophilized with hexadecyltrimethylammonium bromide (HTAB).
The microstructure of nanocomposites was studied by small angle X-ray scattering (SAXS). Additionally, the melting enthalpies (DeltaH(m)), the crystallinities and the half-time of isothermal crystallization were evaluated by differential scanning calorimetry (DSC).
As a result of SAXS experiments for the composite PCL/M-HTAB 90/10, in the temperature range from 313 to 283 K, a rapid change in the interlamellar distance from 3.1 nm to 2.72 nm was observed. Similar scattering curves were obtained for the nanocomposite PCL/M-HTAB 70/30. In the composites containing 50% and 64% wt of M-HTAB, the decrease in interlayer distance was less pronounced in the same temperature range (d(001) 3.15 - 3.2 nm).
DSC results clearly showed that the crystallization is divided into two separate processes: primary crystallization in the PCL matrix, and secondary crystallization.
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Polymers and Polymer Composites, 12(8), 727-737, (2004) |
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18. |
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Molecular dynamics in solid pyridoxine as studied by 1H NMR Spin-lattice relaxation times T-1 and T-1d as well as NMR second moment were employed to study molecular dynamics of pyridoxine (vitamin 136) in the temperature range 10-350 K. The T-1 minimum observed at low temperatures at 200 MHz is attributed to a motion of methyl group. The motion is interpreted in terms of Haupt's theory, which takes into account the tunneling assisted relaxation. At low temperatures, where T-1 is temperature independent, occupation of the ground state only is assumed. A motion of proton of the hydroxyl groups or CH2OH groups probably provides additional mechanism of relaxation, in the high-temperature region.
(C) 2003 Elsevier Inc. All rights reserved. |
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Solid State Nuclear Magnetic Resonance, 25(1-3), 1-4, (2004) |
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19. |
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Studies of water penetration into LDPE-calcium lactate composite Penetration of water into low-density polyethylene-calcium lactate composite is studied with NMR techniques. The presence of filler speeds up the water uptake by the polymer matrix and facilitates polyethylene degradation. Spatial distribution of absorbed water molecules within the composite visualised with MRI corroborates differences in dynamical behaviour of the absorbed water molecules revealed by T-2 measurements.
(C) 2003 Elsevier Inc. All rights reserved. |
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Solid State Nuclear Magnetic Resonance, 25(1-3), 173-176, (2004) |
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20. |
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Molecular dynamics of tert-butyl chloride in CPG studied by NMR The molecular dynamics of tert-butyl chloride (TBC) confined to Controlled Pore Glass matrices of 25 and 7.5 nm were investigated by measuring NMR linewidths, lineshapes, and H-1 and H-2 spin-lattice relaxation times. The behaviour of confined TBC can be explained assuming that the guest molecules form two distinct phases; the surface-affected phase, composed of molecules located at the pore surface, and the bulk-like phase located at the centre of the pores. The bulk-like component of confined TBC, at the temperatures corresponding to the phase III, is characterized by two dynamically different subphases.
(C) 2003 Elsevier Inc. All rights reserved. |
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Solid State Nuclear Magnetic Resonance, 25(1-3), 177-184, (2004) |
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21. |
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Studies of gelation process investigated by fast field cycling relaxometry and dynamical rheology: the case of aqueous low methoxyl pectin solution The Fast Field Cycling Relaxometry and the dynamical rheology were applied to study the gelation process in aqueous low methoxyl pectin solution in the presence of divalent cations from the calcium chloride. The model-free approach to the analysis of H-1 NMRD data was used to separate the information on the static and dynamic behaviour of the system provided by the dispersion profiles of the systems tested. Mechanical spectroscopy was applied as a complementary method to probe the network formation. The structural changes were most pronounced for the concentration of calcium chloride between 10 and 15 mM (the static parameter beta was found to vary from 0.936 x 10(7) to 1.27 x 10(7) 1/s(2)) revealing the sol-gel transition on visual inspection. The presence of the gel network was confirmed by the rheological measurements. All mechanical spectra exhibited the gel like character, and the solid like response was more evident at higher concentrations of calcium cations. The mean correlation time
(C) 2003 Elsevier Inc. All rights reserved. |
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Solid State Nuclear Magnetic Resonance, 25(1-3), 188-193, (2004) |
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22. |
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Rheological and NMR studies of polyethylene/calcium carbonate composites Rheometry, C-13 CP/MAS NMR spectra and H-1 spin-lattice relaxation times T, and Tip have been employed to study the structure and molecular dynamics in composites of polyethylene (LDPE) with calcium carbonate filler. It has been found that the addition of the filler into the polymer leads to an increase in composite rigidity and a decrease in mobility in its crystalline regions. The presence of the filler affects the crystallization process making the crystal structure less perfect and reduces the size of the crystallites.
(C) 2003 Elsevier Inc. All rights reserved. |
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Solid State Nuclear Magnetic Resonance, 25(1-3), 194-199, (2004) |
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23. |
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Proton longitudinal NMR relaxation of poly(p-phenylene sulphide) in the laboratory and the rotating frames reference Spin-lattice NMR relaxation times T-1 in the laboratory frame and T1 as well as Toff in the rotating frame off-resonance were employed to the study of molecular dynamics of both pristine PPS and thermally treated poly(p-phenylene sulfide) (PPS). The temperature dependence of T-1 was exponential in the whole temperature range studied, whereas T1ρ only in low temperatures. In the high temperature range the distribution of relaxation times T1ρ and correlation times tau(c) as well as activation energy E. was observed. The distribution of activation energy determined from T-1 minima at 15 and 30 MHz and from low temperature slopes of T1ρ dependence as well as from spectral density functions (estimated from proton off-resonance technique) was attributed to the reorientation of phenylene groups around the sulfur-phenyl-sulfur axis in amorphous and crystalline phases of PPS. Furthermore, it is suggested that an additional relaxation mechanism related to interactions of protons with paramagnetic centers is operative in a low temperature range. After thermal treatment of PPS the low temperature minima disappeared and the relaxation times shortened in the low temperature regime. Both these facts were attributed to an increased contribution of spin diffusion in the relaxation process.
(C) 2003 Elsevier Inc. All rights reserved. |
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Solid State Nuclear Magnetic Resonance, 25(1-3), 47-52, (2004) |
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24. |
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NMR strong off-resonance irradiation without sample overheating A prototype NMR probe for long RF pulse has been constructed. Its main elements are two coils mounted in the concentric position. The first bigger coil is wound around a glass dewar tube and the second smaller coil is placed inside the dewar. These two coils are thermally isolated by the dewar. A long and strong RF pulse is applied to the bigger coil. The smaller detection coil inside the dewar contains a sample and to this coil a short RF pulse is applied. The two coils are independently tuned and electrically isolated. During the operation of the strong RF pulse the smaller coil has a high resistance to ground (very low Q factor) and does not absorb energy from the bigger coil. During the operation of the short on-resonance RF pulse the bigger coil is detuned to a higher frequency, but the resonance circuit with the small coil is in the electrical resonance. The NMR probe may be used in off-resonance experiments in which long and strong RF pulses are applied to the bigger coil and thereby the problem of the sample overheating is avoided.
(C) 2003 Elsevier Inc. All rights reserved. |
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Solid State Nuclear Magnetic Resonance, 25(1-3), 119-124, (2004) |
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25. |
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Molecular dynamics of n-dodecylammonium chloride in aqueous solutions investigated by 2H NMR and 1H NMR relaxometry Molecular dynamics in n-dodecylammonium chloride/water solutions for concentrations of 34 and 45wt% was studied by 2H NMR and by H-1 NMR dispersion of spin-lattice relaxation in the 2 kHz-90 MHz frequency range. The system exhibits a number of lyotropic liquid crystalline phases, which differ in symmetry and involve motions characterized by a wide frequency scale. The analysis of H-2 NMR lineshapes of selectively deuterated DDACl molecules gave us an evidence for local trans-gauche conformational changes in the chains, whereas the dispersion of spin-lattice relaxation times T, explored by fast field cycling method revealed fast local motions, translational diffusion and collective molecular dynamics of the chains. In particular, we have found that the order director fluctuation mechanism in smectic and nematic phases dominates spin-lattice relaxation below I MHz and that local motions and translational diffusion are responsible for the spin-lattice relaxation in the higher Larmor frequency range.
(C) 2003 Elsevier Inc. All rights reserved. |
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Solid State Nuclear Magnetic Resonance, 25(1-3), 200-206, (2004) |
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26. |
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DSC study of radiostability of 1,4-dihydropyridine derivatives The effect of sterilisation by irradiation has been studied for the seven most often used in medicine derivatives of 1,4-dihydropyridine (nifedipine, nisoldipine, nicardipine, nitrendipine, nimodipine, felodipine and amlodipine). The sterilisation was performed for the compounds in the solid phase with an electron beam of the energy 10 MeV, at room temperature, using the irradiation doses from 20 to 400 kGy. The effects of the irradiation were studied by the methods SEM, DSC, XRD and TLC. The sterilisation with doses 20-100 kGy was found to cause no changes in the physico-chemical properties of the compounds, while the irradiation with higher doses (200-400 kGy) was found to induce changes in the colour, DSC spectrum and TLC picture. As follows from the TLC results, the main product of radiolysis of the compounds studied was a pyridine nitrozoderivative, which indicates the same mechanism of decomposition as in the process of photodegradation. The results prove that the 1,4-dihydropyridine derivatives being highly sensitive to visible and UV radiation are generally resistant to ionising radiation and thus can be subjected to sterilisation by irradiation.
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Journal of Thermal Analysis and Calorimetry, 77(2), 581-596, (2004) |
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27. |
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Thermal analysis in evaluation of the radiochemical stability of some fungicidal drugs Four azole derivatives showing antimycotic activity (Miconazole, Ketoconazole, Clotrimazole, Fluconazole) in solid phase were exposed to beta irradiation at the dose of 20–200 kGy and then alterations in the physicochemical properties of the above derivatives were studied using the methods: scanning electron microscopy (SEM), differential scanning calorimetry (DSC) and X-ray diffraction (XRD) analysis.
It was found that the compounds irradiated with sterilising doses (20–50 kGy) showed no significant alterations in their physicochemical properties, while application of doses >50 kGy resulted in small changes in the X-ray diffraction patterns and in the course of DSC curves, including a decrease in the melting points and enthalpy of the process.
For Miconazole and Fluconazole, a linear and relatively strong correlation was found (from r =0.9782 to r =0.9003) between the size of the dose of irradiation and the decrease in the melting point and enthalpy value.
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Journal of Thermal Analysis and Calorimetry, 77(1), 305-317, (2004) |
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Zaktualizowano: podstrony 2021-06-21 / bazę danych: 2024-11-02 by Webmaster: Zbigniew Fojud