Hysteresiserscheinungen und sog. mechanische Koagulationen von Solen mit stäbchenförmigen Ultramikronen,insbesondere von Vanadinpentoxydsolen,verglichen mit Fibrinsolen

Zusammenfassung Vanadinpentoxydsole enthalten wie Fibrinsole st?bchenf?rmige Ultramikronen, was vor allem H. Diesselhorst und H. Freundlich fanden. Von uns wurden Alterungserscheinungen und Gelatinierungsprozesse, insbesondere die sog. mechanische Koagulation des Vanadinpentoxydsols, die bisher noch nicht beschrieben wurde und die Aehnlichkeit mit der mechanischen Koagulation des Fibrinsols zeigt, zun?chst qualitativ n?her untersucht. Folgende Uebersicht zeigt zusammenfassend die Ergebnisse, die am Vanadinpentoxydsol gewonnen wurden, und stellt sie in Vergleich zu den Befunden am Fibrinsol.     

A general polymer-based process to prepare mixed metal oxides: the case of Zn1-xMgxO nanoparticles

Nanometer-sized mixed metal oxide (MMO) particles (Zn1-xMgxO) with very precise stoichiometry are prepared employing a polymer-based method. The precursor is formed by loading a polyacrylate with metal ions followed by purification of the polymer metal ion complex via repeated precipitation/redissolution cycles. Calcination of the polymer precursor at 550 degrees C gives particles of the metastable solid solution of the ZnO/MgO system in the composition range (x<0.2 and x>or=0.82). The MMO crystal particles are typically 20-50 nm in diameter. Doping of the ZnO by Mg2+ causes a shrinkage of lattice parameter c. Effects of band gap engineering on the optical band gap are reported. The photoluminescence in the visible is also affected, and its maximum shifts from 2.12 eV (pure ZnO) to 2.32 eV at x=0.21. The crystalline MMO particles start to undergo segregation into hexagonal and cubic phases upon annealing at 800 degrees C.     

Competing ordered structures formed by particles with a regular tetrahedral patch decoration

We study the ordered equilibrium structures of patchy particles where the patches are located on the surface of the colloid such that they form a regular tetrahedron. Using optimization techniques based on ideas of evolutionary algorithms we identify possible candidate structures. We retain not only the energetically most favourable lattices but also include a few energetically less favourable particle arrangements (i.e., local minima on the enthalpy landscape). Using suitably developed Monte Carlo based simulation techniques in an NPT ensemble we evaluate the thermodynamic properties of these candidate structures along selected isobars and isotherms and identify thereby the respective ranges of stability. We demonstrate on a quantitative level that the equilibrium structures at a given state point result from a delicate compromise between entropy, energy (i.e., the lattice sum) and packing.     

Electron-transfer polymers. XXXIV. Redox polyurethanes from p-benzoquinone-2,5-diols and diisocyanates

It is possible to prepare polyurethanes from p-benzoquinone-diols and diisocyanates by using dibutyltin diacetate catalyst at room temperature or below, since the benzoquinone group does not react with isocyanate under these conditions. This permits preparation of new redox polymers. In preparing the polyurethanes excess isocyanate groups must be destroyed at the end of the reaction time in order to prevent crosslinking during work-up. These polymers are readily reduced by aqueous hydrosulfite. Good viscosity numbers are obtained; and, in general, upon reduction the viscosity increases over that of the oxidized form. There is no evidence of crosslinking. When oxidized and reduced forms of these polymers are mixed there is no evidence of charge transfer.     

A short introduction to quantum symmetry

In quantum theory, symmetries more general than groups are possible. We give a general definition of a quantum symmetry, such that symmetry operations act on the Hilbert space of physical states and notions of unitarity, invariance and covariance are defined. Within this frame, weak quasi quantum groups are described as a natural generalization of group algebras. Consistency with locality distinguishes them from more general quantum symmetries. To find the new kinds of symmetry one should investigate low dimensional quantum systems such as two-dimensional layers.     

Nomenclature, symbols and definitions in electrochemical engineering (IUPAC Recommendations 1993)

This document treats performance parameters in electrochemical engineering. Nomenclature and definitions for electrochemical engineering together with the respective symbols are given. Parameters to account for electrochemical reactions in electrolysis as well as for electrochemical power sources (electrochemical energy generators) are included in this document.