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od 2020-09-20 |
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1. |
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Lamellar ordering in computer-simulated block-copolymer melts by a variety of thermal treatments A lattice computer simulation of a symmetric A-B-A triblock copolymer melt is reported. This melt is quenched, in simulation, from an athermal state to 39 different temperatures using cooperative motion algorithm. Energy, specific heat, copolymer end-to-end distance, bridging fraction, lamellar spacing, concentration profiles, and microstructure visualizations are reported. The quenching simulation results are compared with those obtained by alternative thermal treatments, that is by slow heating and slow cooling. Quenches yield data consistent with theory and experiment, whereas slow cooling and slow heating results do not capture the expected behavior for the lamellar spacing and the bridging fraction. Finally, at very low temperatures, below the conventional order-disorder transition temperature, an additional ordering is recorded, from a conventional lamellar phase to a lamellar structure showing copolymer junction points condensed into a two-dimensional plane.
(C) 2003 American Institute of Physics. |
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Journal of Chemical Physics, 119(21), 11451-11457, (2003) |
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2. |
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Brittle-ductile transition (BDT) recycled poly(ethylene-terethalate) - PET The paper is concerned with the influence of reprocessing on molecular, rheological and mechanical properties of recycled polymers. The injection moulded specimens made of virgin and recycled material after 4-cycles and 6-cycles of processing poly(ethylene terephthalate) - PET EASTAPAK 9921 were investigated. The deformation and character of cracking (brittle-ductile) were determined from the analyse of stress-strain curves as a function of temperature. The brittle-ductile transition was characterised by the Ludwig- Davidenkov-Orowan (LDO) criterion. The mechanical behaviour was assessed in tensile testing at 250 mm/min and at various temperature. The results showed that the point of brittle-ductile transition (BDT) shifts to higher temperature and to lower stress. The character of fracture was taken using a TESCAN scanning electron microscope (SEM). The thermal properties of a virgin and recycled PET (glass transition, melting point and crystallinity) were characterized by differential scannning calorimetry (DSC). Solution viscosity measurements were carried out in an viscosimeter equipped with Ubbelhode capillaries. The investigation showed that the recycling polymers cause the degradation of polymer what is evidenced in intrinsic viscosity, average molecular weight and the degree of crystallinity recycled poly(terephthalate ethylene). This effect caused the increase of brittleness and reduced the load-carrying of products made from recycled polymers.
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Polymer Processing Society PPS-20, 204, (2003) |
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(Pobrane: 2020-10-23) |
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3. |
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In vivo natural-abundance 17O/1H MRI of Rhesus monkey brain with whole-body scanner and homebuilt multinuclear accessory The construction of an accessory to commercial whole-body magnetic resonance imaging (MRI) scanners that provides multinuclear capability is described. The multinuclear system has access to all clinical pulse sequences and is not limited by the frequency range of the commercially available "spectroscopic package". The accessory was used for O-17 studies with a homebuilt birdcage resonator and a low-noise preamplifier. In vivo O-17 images of a rhesus monkey brain were obtained. The homebuilt birdcage was transparent to radio-frequency irradiation of the scanner's body coil at H-1 frequency allowing consecutive acquisitions of H-1 and O-17 images and their superposition. The results demonstrate the potential of O-17/H-1 imaging with whole-body scanners.
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Applied Magnetic Resonance, 24(3-4), 393-400, (2003) |
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4. |
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Combined 17O/1H MRI study in a whole-body scanner A simple method of obtaining consecutive H-1 and natural-abundance O-17 images is described with a scanner's original body resonator (for H-1) and a homemade linear birdcage (for O-17). Two kinds of experiments were performed to test the method. In the first experiment, a proton image of the phantom was acquired with a whole-body resonator. In the second experiment, the phantom was inserted into an oxygen birdcage resonator and imaged again with a whole-body resonator. The intensities of images resulting from the experiments were analyzed. Although the B-1 field homogeneity is disturbed, the proton images acquired with a whole-body resonator when the oxygen resonator is present are of acceptable quality for use in the combined O-17/H-1 imaging.
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Applied Magnetic Resonance, 24(3-4), 409-415, (2003) |
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5. |
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Polyolefin miscibility: solid-state NMR investigation of phase behaviour in saturated hydrocarbon blends Chain-level mixing in polyolefins is investigated for blends of polyisobutylene (PIB) and polyethylene-co-1-butene (PEB). Previous reports suggest that PIB exhibits unusual mixing behavior in certain saturated blends relative to other polyolefins, even though it is immiscible with most. Variable-temperature H-1, H-2, C-13, and Xe-129 NMR experiments are used to characterize local PIB chain dynamics in blends with PEB in which the concentration of 1-butene comonomer units is 23 or 66 wt %. Results from 1D and 2D solid-state C-13 exchange experiments, H-1 relaxation measurements, and H-2 line shape analysis indicate that local conformational dynamics of the PIB CH2 group in the polymer backbone increase significantly in blends with PEB copolymers containing 66 wt % butene comonomer (PEB-66). Even though the PEB-66 is a higher Tg polymer than PIB, PIB exhibits a lower effective Tg when the blend is formed relative to its pure state. Similar perturbations are not observed in the PIB/PEB-23 blend, indicating that this blend is not miscible at the chain level. These results are directly relevant to the length scale of glass transitions in polyolefins, indicating that local interchain packing plays an important role in the conformational dynamics that occur within a chain, and are suggestive of local configurational entropy contributions to mixing. Although H-1 spin-diffusion experiments could not reveal quantitative length scales of mixing in the these blends due to insufficient contrast between the constituents, Xe-129 NMR experiments showed that the PIB/PEB-66 blend was homogeneous on a 50 nm length scale. In agreement with the heterogeneous morphology indicated by the dynamic NMR experiments, Xe-129 NMR showed two resolved peaks for the PIB/PEB-23 blend, indicative of phase separation on a 50 nm length scale. The compilation of all the data, most of which was obtained at natural abundance, indicates that the PIB/PEB-66 blend exhibits intimate chain-level mixing on a length scale much shorter than R-g (ca. 8 nm). More importantly, the data show that reduced chain packing constraints occur in the miscible blend and suggest that local entropic contributions are the driving force for miscibility.
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Macromolecules, 36(13), 4844-4850, (2003) |
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6. |
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Polarisation and energy barriers in ferroelectric pyridinium tetrafluoroborate The measurements of 1H and 19F NMR second moment were performed for a polycrystalline sample of (PyH)BF4, whereas the shape of 2H NMR line was analysed for a polycrystalline sample of (d5PyH)BF4. Asymmetry parameter D has been calculated for four models of pyridinium cation reorientation among inequivalent potential energy minima, using experimental value of 1H NMR second moment as well as the 2H NMR line width. Knowing the potential shape and the population of its minima the temperature dependence of polarisation for all the models has been found. From the comparison of the experimentally determined polarisation with the calculated one the most appropriate model of the pyridinium cation reorientation has been chosen.
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Molecular Physics, 101(10), 1469-1476, (2003) |
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7. |
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Evaluation of radiostability of some steroid derivatives The effect of ionising radiation (15-100 kGy) on the physico-chemical properties of 6 steroid derivatives in solid state (Hydrocortisone, Hydrocortisone acetate, Prednisolone, Prednisolone acetate, Dexamethasone and Fludrocortisone acetate) was studied by differential scanning calorimetry (DSC), differential thermal analysis (DTA), scanning electron microscopy (SEM), UV spectrophotometry, high-performance liquid chromatography (HPLC), X-ray powder diffraction and polarimetry. DSC and DTA results revealed that the irradiated compounds undergo phase transitions at lower temperatures, show lower melting points and lower enthalpy of the melting process their non-irradiated analogues. The results of HPLC measurements proved a loss in the active substance content after irradiation ranging from 0.5 to 2.88%. No significant effect of irradiation was detected by the UV spectrophotometry or polarimetry in the course of the UV spectrum, absorbancy or optical rotation, as well as in the SEM photographs and X-ray patterns. For some compounds studied a correlation was found between the irradiation dose and the shifts in DSC curves and the loss of content determined by the HPLC method. Similar, but not so much pronounced relations were established in or earlier studies of the derivatives of nitroimidazole and 1,4-dihydropyridine. In general the results have shown relatively high radiochemical stability of the compounds studied and have proved that the DSC method is a sensitive detector of irradiation-caused changes in drugs in solid phase.
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Journal of Thermal Analysis and Calorimetry, 73, 473-485, (2003) |
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8. |
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Adsorption of the quaternary ammonium salts on montmorillonite Sodium montmorillonite SOMASIF((R)) ME 100 (M) has been subjected to modification through ion-exchange reaction by a number of (alkyloxymethyl)dodecyldimethylammonium chlorides with the general formula [C12H25N+(CH3)(2)CH2OR]Cl-. The modified samples were studied by X-ray diffraction (XRD) technique, Fourier transform infrared (FTIR) spectroscopy and scanning electron microscopy (SEM), and thermogravimetric analysis. The basal spacing of unmodified montmorillonite, determined by XRD, was 1.227 nm and after modification it increased up to 1.557 nm (montmorillonite modified with dodecyldimethyl(dodecyloxymethyl)ammonium chloride). The FTIR studies revealed structural differences between the modified and unmodified montmorillonite samples. The IR spectra of the modified montmorillonite showed the C-C stretching bands (1468 cm(-1)) and C-H vibrations (near 2930 and 2856 cm(-1)). Results of the SEM study revealed a tendency towards lump formation and agglomeration of the organophilised particles of montmorillonite.
(C) 2003 Elsevier Ltd. All rights reserved. |
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Journal of Physics and Chemistry of Solids, 65(2-3), 441-445, (2003) |
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9. |
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Influence of silane modification of kaolins on physico-mechanical and structural properties of filled PVC composites The paper presents the results of a study of the potential of modified kaolin as a filler for PVC. Kaolin from Maria III deposits in Poland was used. Aminosilanes and mercaptosilanes were used to modify the surface. Basic physicochemical parameters, such as the absorption capacity of the plasticiser, the heat of immersion in hydrophobic and hydrophilic solvents, and the morphology of particles of the modified filler were characterised. The modified kaolins clearly improved the physico-mechanical properties of PVC, in particular, they increased the elongation of PVC, when used at 10% and 15% w/w levels in the composite. Some studies of the microstructure of the filled composites were also performed using small angle X-ray scattering (SAXS) and scanning electron microscopy (SEM) techniques.
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Polymers and Polymer Composites, 11(5), 397-406, (2003) |
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10. |
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The microstructure and mechanical properties of new HDPE-chalk composites Increasing demands on the quality and specific properties of polymers imply increasing demands on the mineral fillers used in composite materials. They are expected not only to reduce the cost of production but also improve the mechanical properties of the composites or endow them with new features, e.g. thermostability. The paper presents a method for obtaining polyethylene composites with chalk modified by two new 1-alcoxymethyl-3-hydroxypyridinium chlorides: 3-hydroxy-1-octyloxymethylpyridinium chloride (salt 1) and 3-hydroxy-1-octadecyloxymethylpyridinium chloride (salt 2) and gives a characterisation of the composites obtained. Introduction of chalk modified with ammonium salts results in an increased values of MFI of the composites. The MFI changes are the most pronounced for the PE composites containing the filler in concentrations from 0.05 to 2.0% wt. Addition of the chalk modified with the ammonia salts causes greater changes in some mechanical properties of the composites (Young modulus) than addition of unmodified chalk, while changes in some other properties (stress at break) was practically the same.
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Physicochemical Problems of Mineral Processing, 37(1), 141-147, (2003) |
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11. |
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Chemistry for Agriculture, 4, 410-414, (2003) |
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(Pobrane: aktualizowanie) |
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12. |
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Badania SAXS i DSC nanokompozytów poli(epsilon-kaprolakton)/organofilizowany montmorylonit Nanokompozyty otrzymano na drodze interkalacyjnej polimeryzacji kaprolaktonu w obecności 10% i 50% wag. syntetycznego montmorylonitu sodowego organofilizowanego bromkiem heksadecylotrimetyloamoniowym (HTAB). Badania strukturalne uzyskanych nanokompozytów przeprowadzone techniką małokątowego rozpraszania promieni X przeprowadzone w zakresie -50˚ ± 70˚ dowiodły, że odległość międzypłaszczyznowa d0001 oraz stopień uporządkowania układu rosną wraz ze wzrostem temperatury. Aby wyjaśnić naturę obserwowanych przemian, próbki przebadano techniką różnicowej mikrokalorymetrii skaningowej (DSC). W oparciu o wyniki eksperymentów SAXS i DSC stwierdzono, że skok wartości d001 obserwowany w zakresie 0-45 ˚C spowodowany jest procesem krystalizacji PCLw matrycy oraz w obrębie galerii krzemianu. Zmiany poniżej i powyżej tego zakresu są efektem rozszerzalności termicznej polimeru zawartego w przestrzeniach międzypłaszczyznowych montmorylonitu.
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Prace Naukowe Instytutu Technologii Organicznej i Tworzyw Sztucznych Politechniki Wrocławskiej, 52, 381-384, (2003) |
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(Pobrane: 2020-10-25) |
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Zaktualizowano: podstrony 2021-06-21 / bazę danych: 2024-04-23 by Webmaster: Zbigniew Fojud