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ABSTRACT: For diblockcopolymers of polybutadiene-poly(ethyleneoxide) (PB-PEO) type, water is a selective solvent. In dependence of the length of both blocks and the block length ratio, these polymers form a multitude of self-assembled structures in solution. In the present work scattering methods are used to investigate the water-soluble polymer PB125-PEO155 . It is found to form long rodlike micelles, which are characterized with respect to the aggregate length L , the cross sectional radius RCS , the radial scattering length density profile sigma r, and the radial aggregation number Nrad. Model-independent as well as model-based approaches are used for the scattering data analysis. From dynamic light scattering (DLS) and static light scattering (SLS) experiments the weight averaged length Lw of these stiff elongated aggregates is determined to Lw=350 nm . Small angle neutron scattering (SANS) reveals a cross sectional radius of RCS=17 nm and in combination with results from the SLS the radial aggregation number is found to be Nrad=70 .
Physical Review E 11/2004; 70(4 Pt 1):041408. · 2.26 Impact Factor
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ABSTRACT: The present contribution presents the single-step preparation and characterization of poly(N-isopropyl acrylamide)-co-polystyrene core-shell microgels with varying polystyrene content. The swelling behavior of the particles is investigated using dynamic light scattering and differs significantly from the swelling behavior of poly(N-isopropyl acrylamide) homopolymer particles. The lower critical solution temperature is found to be shifted to lower temperatures upon increasing the polystyrene content of the particles. The core-shell structure of the particles is revealed by means of small angle neutron scattering (SANS) using the method of contrast variation. Additionally, the formation of mesoscopic crystals of these particles is investigated by means of scanning electron microscopy and also by SANS. The particles seem to have preferable properties with respect to crystallization compared to homopolymer microgels.
Langmuir 06/2004; 20(11):4330-5. · 4.19 Impact Factor
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ABSTRACT: Using small-angle neutron scattering, we have imaged the magnetic flux line lattice (FLL) in the d-wave heavy-fermion superconductor CeCoIn5. At low fields we find a hexagonal FLL. Around 0.6 T this undergoes what is most likely a first-order transition to square symmetry, with the nearest neighbors oriented along the gap node directions. This orientation of the square FLL is consistent with theoretical predictions based on the d-wave order parameter symmetry.
Physical Review Letters 06/2003; 90(18):187001. · 7.37 Impact Factor
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ABSTRACT: Large grain melt processed Y-Ba-Cu-O (YBCO) samples have been prepared by seeded and unseeded growth techniques. The current carrying ability within individual grains and across grain boundaries has been investigated and correlated with features in the microstructure of samples fabricated by both techniques. The development of an inhomogeneous, cell-like growth microstructure in seeded samples at distances ≈4 mm from the seed is related to a saturation in inclusion density and volume proportion of Y2BaCuO5 (Y211) particles. A significant decrease in critical current density is associated with this change over a wide temperature range. The resistance of high angle c-axis grain boundaries is observed to depend critically on the magnitude of the injection current whereas the intra-granular resistance is not influenced significantly by this variable. Jc of a grain boundary fabricated by unseeded melt growth is estimated to be less than 100 A cm−2 at 77 K in zero applied field, which is more than two orders of magnitude lower than the intragranular Jc. Field screening measurements suggest that low angle grain boundaries do not form weak links between grains in modest magnetic fields and hence do not present a significant barrier to current flow.
Applied Superconductivity 4:507-517.
