Colloidal gold adsorbed onto positively charged substrates forms a two-dimensional layer with a maximum coverage of 1 colloid/1000 nm 2 as shown by optical absorption spectroscopy, small-angle X-ray scattering, and atomic force microscopy. Positively charged substrates are obtained by either chemisorption of endgroup-functionalized silanes or by polycation adsorption. Bulk diffusion controls the gold adsorption; thus lower coverages can also be achieved. The optical spectra not only contain information on single colloids but also on their mutual interactions, as well as on the polymeric and solvent environments. Absorption spectra based on Mie and Maxwell-Garnett theory are calculated. The films remain stable on exchange of the external solvent. The local dielectric environment is shown to not only influence the position of the absorption band but also, more drastically, the intensity (by a factor of 2.5), in agreement with theoretical predictions ((15%). Particle aggregation induced by branched polycations causes an additional low-energy absorption peak.

Di- and triblock copolymers of tert-butyl methacrylate (tBMA) and 2-(N-methylperfluorobutanesulfonamido)ethyl methacrylate (FMA) were synthesized by sequential anionic polymerization. These polymers were characterized by size-exclusion chromatography and 1H and 19F NMR spectroscopy. The microphase separation of bulk samples was studied by atomic force microscopy and small-angle X-ray scattering. Thermal annealing of the block copolymers at 200 °C yielded inter- and intramolecular anhydrides due to the splitting of the ester having tert-butyl groups connected with isobutene formation. This conversion was followed by time-resolved Fourier transform infrared (FT-IR) spectroscopy. The anhydrides can be transformed into the sodium salt of methacrylic acid units in 1 N NaOH under reflux. The thermal ester splitting of the tBMA block at 200 °C did not influence the FMA block. The obtained block copolymers were soluble in water when the FMA content was less than 10 mol %. The behavior of these solutions was studied by various experimental methods. The critical micelle concentration was obtained by surface tension measurements. The micelle dimensions were determined by dynamic light scattering. The size and inner structure of the micelles were investigated by small-angle X-ray scattering and could also be observed by transmission electron microscopy after transfer of the diluted solutions onto carbon films. Typical polyelectrolyte effects were observed by viscosity measurements for PtBMA only. For block copolymers the aggregation behavior is dominating even at very low concentrations.

We investigate the self‐organization of PSS in brushes and polyelectrolyte multilayers with X‐ray, neutron and optical reflectivity. The electrostatic force dominates brush phases and adsorption behavior, additionally we find evidence of a strong hydrophobic force: (ι) within amphiphilic diblock copolymer monolayers, a PSS monolayer adsorbs flatly to the hydrophobic block, (ιι) on temperature increase (and with screened electrostatic forces), more PSS is adsorbed onto oppositely charged surfaces, and (ιιι) a polyelectrolyte multilayers shrinks when heated at 100% r.h. The latter two effects are consistent with the well‐known increase of the hydrophobic force on heating: The increased PSS surface coverage can be attributed to deteriorating solvent conditions. Within a polyelectrolyte multilayer, an increase of the hydrophobic force maximizes the local contact of hydrophobic polymer segments, causing a reduction of swelling and an increased mass density.

The polarizability R of gold nanocolloids (radius R, number density N) with a shell characterized by a thickness d and a dielectric constant ε s immersed in a medium with dielectric constant ε m is given by 2,3 ε is the dielectric constant of gold, which is a complex number with a pronounced dependence on the wavelength. 4 Then, one obtains for the effective dielectric constant ε eff of the core-shell system in the mediumThe experimentally accessible variable is the extinction coefficient γ ) 4πκ/λ, with κ as the imaginary part of ε eff . 5 To verify the equations, extinction spectra for gold coreshell particles (R ) 7.5 nm) are calculated for two cases ( Figure 1) describing the shell: constant dielectric constant ε s with increasing thickness d and constant thickness d with increasing dielectric constant ε s . In both cases, an increase in the maximum extinction as well as a shift of the maximum position to longer wavelengths is observed. Whereas in the former case both effects show saturation for d ≈ 15 nm (Figure 2), limiting the sensitivity of the method to shells with 8 nm thickness, in the latter case both the peak maximum and red shift increase linearly with the dielectric constant, ε eff , independent of d. If d approaches zero, then the equation is that of a naked colloid with radius R. However, if d exceeds 20 nm, then one obtains the spectrum of a naked colloid immersed in a medium with ε s . Finally, we mention that with an increase in the nanoparticle radius a shell thickness exceeding 15 nm can be readily distinguished.Acknowledgment. We thank Junfeng Zhai (Chinese Academy of Sciences, Changchun) for bringing the problems in the paper to our attention. Financial support by SFB TR 24 is appreciated. We also thank Olaf Soltwedel for preparing the plots, and verified that the extinction in the limit of large and small shell thickness was sensible.

The phenomenological tradition within human geography continues to inspire research on everyday city life. This paper draws on David Seamon's notion of place ballet to understand the meaning of encounters between older people visiting an urban park in the city of Eindhoven, the Netherlands. The paper uses participant observation, including a serial interviewing strategy in which older people are accompanied on their walks through the park, to expose daily walking routines. As part of these routines, characterised by clockwork precision, they meet fellow park visitors in place ballet. Place ballet is associated with recurring encounters between familiar strangers that are full of significance. Notably, it sustains an atmosphere of fellowship that encourages people to notice, and care for, each other. These findings support the view that the phenomenological perspective emphasises the meaningful and positive aspects of encounters between older people in public space, even if they do not necessarily interact.

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