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The detailed Tc-sensitive crystal pattern transition from dendrites through fourfold-symmetric structures to faceted crystals of ultrathin poly(ethylene oxide) films has been experimentally observed using atomic force microscopy. The transition has been quantitatively described by the Tc-dependences of the fractal dimension and of the velocity ratio caused by forward and transverse growths in crystal tips. The essential aspect of the pattern selection and transition is mainly the competition of two macroscopic mechanisms: Nucleation-limited and diffusion-limited growths which create faceted and dendritic crystal patterns, respectively. Their combination is a facet growth within a diffusion field which will create a faceted dendrite. [ABSTRACT FROM AUTHOR]

Nondispersive hole transport in two polyspirobifluorene copolymers containing either 10% anthracene or 10% carbazole was studied in detail by the charge-generation layer time-of-flight (TOF) technique over a wide range of electric fields and temperatures. The TOF transients of both polymers showed a clear plateau indicating nondispersive transport of charge carriers. Zero-field mobilities were found to be in the order of 10-6 cm2/V s at room temperature. Results were analyzed within the framework of the Gaussian disorder model to extract the parameters of the charge-carrier transport. The width of the transport density of states was determined to be 83 meV for the polyspirobifluorene-anthracene copolymer and 89 meV for the polyspirobifluorene-carbazole copolymer. At lower temperatures a change of slope in the temperature dependence of the zero-field mobility was observed. At higher temperatures the TOF transients were modified by a cusp. Both phenomena can be explained within the framework of the Gaussian disorder model. [ABSTRACT FROM AUTHOR]

Hole transport in a polyspirobifluorene homopolymer and a statistical polyspirobifluorene-triarylamine copolymer has been studied in detail employing the charge-generation layer time-of-flight (TOF) technique over a wide range of electric fields and temperatures. Both materials exhibit nondispersive TOF signals after injection of a sheet of charge carriers from a thin (10 nm) perylene-diimide charge-carrier generation layer into a relatively thick (d>1 μm) polymer film. Results were analyzed within the framework of the Gaussian disorder model and the charge transport parameters were extracted for both polymers. The zero-field hole mobility of the spirohomopolymer was found to be on the order of 10-6 cm2/V s, whereas the copolymer showed a considerably lower hole mobility of 6×10-8 cm2/V s. The width of the density of states σ was determined to be 86 meV for the homopolymer and 107 meV for the copolymer. The latter polymer also showed an increased positional disorder due to the statistically incorporated triarylamine units. [ABSTRACT FROM AUTHOR]

The photoluminescence (PL) properties of oligofluorenes with 2-ethylhexyl group in 9, 9′ position in solution and as thin films were investigated by time-resolved techniques at both room temperature and 77 K. The fluorescence lifetimes of the oligomers decrease with chain length. The lifetimes τ follow the relation τ=386+808(1/n) (ps) where n is the number of fluorene units in the oligomer. Concentration and laser excitation energy dependences of PL spectra of the oligofluorenes are also given. Phosphorescence was observed for oligofluorenes in the frozen matrix of MTHF at 77 K. The lifetime of phosphorescence increases with increasing molecular length. Similar emission bands were observed for oligofluorenes with a central ketogroup. A lifetime analysis clearly reveals that the “green emission” of the oligomers free of ketogroups results from a phosphorescence with lifetime τ of 3 ms while the green emission from the keto-oligomer is a fluorescence from a charge transfer π-π* level of τ=8 ns. [ABSTRACT FROM AUTHOR]

Upconversion-induced fluorescence in platinum-octaethylporphyrin (PtOEP)-doped thin films of a spirobifluorene-anthracene copolymer has been investigated. Upon exciting in the range of the absorption band (2.31 eV, 537 nm) of the guest molecules, blue fluorescence (2.75 eV, 450 nm) from the spirobifluorene host was observed. The intensity of the upconverted emission was found to be one order of magnitude higher than from a PtOEP doped but anthracene-free spirobifluorene copolymer and than previously reported for metallated porphyrin-doped polyfluorene samples. It is argued that the efficient upconversion originates from the triplet energy transfer from the phosphorescent dopant to the sensitive unit of the host polymer, followed by triplet-triplet annihilation and finally blue emission from the spirobifluorene host polymer backbone. [ABSTRACT FROM AUTHOR]

An amphiphilic diblock codendrimer composed of a third generation poly(methallyldichloride) end-capped by eight hydroxyl groups (PMDC[(OH).sub.8]) and a second-generation poly(urethane amide) end-capped by four alkyl groups (PUA[(C16).sub.4]) are self-assembled into highly oriented ribbons at the water-air interface. The analysis of the ribbon formation has shown that the ribbons are hierarchically self-organized by the janus and plate-like shape of g3-PMDC[(OH).sub.8]-b-g2-PUA[(C16).sub.4].

Solid-state NMR under fast magic-angle spinning is used for studying the structure and the local proton mobility of poly(vinyl phosphonic acid) (PVPA). The studies have shown that the proton motion of PVPA is mediated by acidic protons through hydrogen-bonded network and condensation of phosphonic acid groups has blocked the percolation passage for proton conduction, resulting in the decrease in the conductivity.

The precipitation of zinc oxide from an aqueous solution in the presence of poly latex nanoparticles is used for the synthesis of micro- and submicrosized ZnO-polymer hybrid materials. The electron paramagnetic resonance (EPR) study of the polymers provides a lot of information about the crystal defects and species with unpaired electrons, though it has different physical origin as compared to the green-yellow emission.

Nanometer-sized mixed metal oxide (MMO) particles [Zn.sub.1-x][Mg.sub.x]O with precise stoichiometry are prepared using a polymer-based method. Doping of ZnO by [Mg.sup.2+] causes a shrinkage of lattice parameter C.

The application of molecular modeling to study problems related to the packing and conformation of oligofluorene molecules in the solid state is described. The simulations have shown that this configuration is sterically and energetically unfavorable so that formation of an excimer following optical excitation appears to be unlikely.

With the beginning of the Napoleonic war at the turn of the 19th century, capitalist transformation in the German states and in the Habsburg Empire took different routes. The article analyses the political economy of both types of ‘defensive modernization’ from the viewpoint of institutional economics. We argue that initial reforms in German states gave way to a transformation process which drove a wedge between the interest of the monarchs and the landed nobility. Liberal reformers established a political bargain with the nobility which made capitalist institutions acceptable for the power holders. Later on, reformers established a ‘market preserving federalism’ which gave capitalism a further boost. By contrast, the dependence of the Austrian Emperor on the multiethnic nobility weakened the power of the central state. The transformation process in the Habsburg Empire remained dependent on the personal interests of the dominant coalition, which either delayed capitalism or sought to combine capitalism with protectionism on its own behalf. As a result, capitalist dynamics took up speed in Germany but were delayed in Austria. [ABSTRACT FROM PUBLISHER]