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51.
Schweiger M Seidel SR Arif AM Stang PJ 《Angewandte Chemie (International ed. in English)》2001,40(18):3467-3469
52.
We investigate polyelectrolyte brushes in the osmotic regime using both theoretical analysis and molecular dynamics simulation techniques. In the simulations at moderate Bjerrum length, we observe that the brush height varies weakly with grafting density, in contrast to the accepted scaling law, which predicts a brush thickness independent of the grafting density. We show that such behavior can be explained by considering lateral electrostatic effects (within the non-linear Poisson-Boltzmann theory) combined with the coupling between lateral and longitudinal degrees of freedom due to the conserved polymer volume (which are neglected in scaling arguments). We also take the non-linear elasticity of polyelectrolyte chains into consideration, which makes significant effects as chains are almost fully stretched in the osmotic regime. It is shown that all these factors lead to a non-monotonic behavior for the brush height as a function of the grafting density. At large grafting densities, the brush height increases with increasing the grafting density due to the volume constraint. At small grafting densities, we obtain a re-stretching of the chains for decreasing grafting density, which is caused by lateral electrostatic contributions and is controlled by the counterion-condensation process around polyelectrolyte chains. These results are obtained assuming all counterions to be trapped within the brush, which is valid for sufficiently long chains of large charge fraction.Received: 14 May 2003, Published online: 11 November 2003PACS:
61.25.Hq Macromolecular and polymer solutions; polymer melts; swelling - 36.20.-r Macromolecules and polymer molecules - 61.20.Qg Structure of associated liquids: electrolytes, molten salts, etc. 相似文献
53.
Gerald Steiner Valdas Sablinskas Wolfgang Seidel Reiner Salzer 《Analytical and bioanalytical chemistry》2009,395(6):1641-1650
Polarization modulation infrared reflection absorption spectroscopy (PM-IRRAS) is a very sensitive technique to characterize
the degree of molecular ordering in thin films on metallic surfaces. This is the first report of the coupling of a PM-IRRAS
microscope to a free electron laser (FEL), a light source of highest brilliance. Some FELs emit in the infrared region and
permit the mapping of molecular properties at high lateral resolution. We studied the molecular orientation of octadecanephosphonic
acid (OPA) attached to a gold surface with microstructured aluminum oxide islands on the gold. The spatial resolution achieved
is 12 μm which corresponds to the diffraction limit of the infrared light used in this study. This is a substantial improvement
compared to previous studies using a PM-IRRA accessory together with a commercial Fourier transform infrared spectrometer,
where the lateral resolution is noise-limited rather than diffraction-limited. The spectral maps reveal that OPA is preferably
attached to the aluminum oxide islands via the bidentate binding mode whereas the tridentate mode is dominating in case of
OPA attached to the gold areas. 相似文献
54.
H. Kühl R. Rüter J. Micka K. Vrana C. W. Herd A. J. Amos K. Fuchs W. Ruziczka E. Kohn K. Seidel und D. W. Kent-Jones 《Fresenius' Journal of Analytical Chemistry》1931,84(1-2):57-61
Ohne Zusammenfassung 相似文献
55.
We consider exact Lagrangian submanifolds in cotangent bundles. Under certain additional restrictions (triviality of the fundamental
group of the cotangent bundle, and of the Maslov class and second Stiefel–Whitney class of the Lagrangian submanifold) we
prove such submanifolds are Floer-cohomologically indistinguishable from the zero-section. This implies strong restrictions
on their topology. An essentially equivalent result was recently proved independently by Nadler [16], using a different approach. 相似文献
56.
57.
Rapid methods for the quantification of Escherichia coli are required for the monitoring of faecal contamination in water to secure public health. The immunomagnetic separation (IMS) offers rapid enrichment and purification of bacteria in complex matrices and is compatible with immunoassays. By means of this technique, non-target cells and matrix components which might interfere with subsequent analytical methods are removed. We present the synthesis of magnetic nanoparticles (MNPs) and covalent coupling to antibodies against the enterobacterial common antigen (ECA) for use with IMS. Quantification was carried out with a chemiluminescence-based sandwich enzyme-linked immunosorbent assay (ELISA). Our anti-ECA-MNPs allow for a group-specific enrichment of bacterial cells, which can be combined with a species-specific analytical method. The particles were used along with commercially available magnetic columns for the selective enrichment of E. coli from 10-mL water samples. The volumetric enrichment factor was 9. For enriched samples, the limit of detection was reduced from 5.0?×?106 cells·mL-1 to 2.6?×?105 cells·mL-1. Using 200 µL anti-ECA-MNPs, we determined a recovery of 97?±?6% for a sample containing 106 cells·mL-1 and 89?±?2% for a sample containing 107 cells·mL-1. The overall time for cell enrichment and detection was 3 h 45 min. 相似文献
58.
We report on generation of a 20 nm wide, 35 GHz repetition rate optical frequency comb in a magnesium fluoride whispering gallery mode resonator pumped with 2 mW of 1543 nm light. The high efficiency of comb generation is associated with the small anomalous group velocity dispersion of the resonator. Growth dynamics of the comb is studied and compared with earlier theoretical predictions. 相似文献
59.
60.