On a method of measuring diffusion coefficients of solid materials

In a certain method for measuring diffusion coefficients of solid materials a circular cylindrical sample of the material is clamped between annular rings and the difference in concentration between the end surfaces and the flux through the sample are measured. In order that the diffusion coefficient can be determined from these data a certain factor which depends on the geometry of the sample must be known. In this note two complementary variational principles are derived and used to obtain precise upper and lower bounds for this factor.

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Zusammenfassung Bei einem Verfahren zur Messung von Diffusionskoeffizienten von Feststoffen wird eine zirkulärzylindrische Stoffprobe zwischen zwei ringförmingen Haltern eingespannt. Der Konzentrationsunterschied zwischen den Endflächen und dem Flux werden gemessen.Um bei diesem Verfahren den Koeffizient bestimmen zu können, muss ein Faktor, der von der Geometrie der Einspannungsvorrichtung abhängt, bekannt sein. In dieser Arbeit werden zwei komplementäre Variationsprinzipien hergeleitet, die dann anschliessend für die Berechnung von genauen oberen und unteren Schranken dieses Faktors angewandt werden.

     

Glueball mass calculations on an array of computers

We have calculated the mass of the 0⁺ glueball in SU(2) pure gauge theory in 4 dimensions, with very high statistics. The computation was done on an array of microprocessors with nearest-neighbor connections which run concurrently. We discuss, in detail, the implementation of the pure gauge algorithm for SU(2) and SU(3) and also the algorithm for calculating arbitrarily shaped Wilson loops on the array. The extension of these algorithms to the inclusion of dynamical fermions is also discussed. Finally, we present the results of our variational calculation of glueball masses which are in agreement with published results.     

Die Konstitutionsabhängigkeit und die benzolinduzierten Effekte der chemischen Verschiebungen der Methoxyprotonen einiger Carbonsäuremethylester

The Chemical shifts of the methoxyprotons in about 60 methyl esters of carboxylic acids were obtained in CCl₄ and C₆D₆, and their dependence on constitution and solvent are discussed. It was shown that the values of a certain molecule could be assumed to be composed additively of a number of parameters which characterise the substituents.     

The relationship between nanoscale architecture and function in photovoltaic multichromophoric arrays as visualized by Kelvin probe force microscopy

The physicochemical properties of organic (multi)component films for optoelectronic applications depend on both the mesoscopic and nanoscale architectures within the semiconducting material. Two main classes of semiconducting materials are commonly used: polymers and (liquid) crystals of small aromatic molecules. Whereas polymers (e.g., polyphenylenevinylenes and polythiophenes) are easy to process in solution in thin and uniform layers, small molecules can form highly defined (liquid) crystals featuring high charge mobilities. Herein, we combine the two material types by employing structurally well-defined polyisocyanopeptide polymers as scaffolds to precisely arrange thousands of electron-accepting molecules, namely, perylenebis(dicarboximides) (PDIs), in defined chromophoric wires with lengths of hundreds of nanometers. The polymer backbone enforces high control over the spatial location of PDI dyes, favoring both enhanced exciton and charge transfer. When blended with an electron-donor system such as regioregular poly(3-hexylthiophene), this polymeric PDI shows a relative improvement in charge generation and diffusion with respect to monomeric, aggregated PDI. In order to correlate this enhanced behavior with respect to the architecture, atomic force microscopy investigations on the mixtures were carried out. These studies revealed that the two polymers form interpenetrated bundles having a nanophase-segregated character and featuring a high density of contact points between the two different phases. In order to visualize the relationship between the architecture and the photovoltaic efficiency, Kelvin probe force microscopy measurements were carried out on submonolayer-thick films. This technique allowed for the first time the direct visualization of the photovoltaic activity occurring in such a nanoscale phase-segregated ultrathin film with true nanoscale spatial resolution, thus making possible a study of the correlation between function and architecture with nanoscale resolution.     

A combined experimental and theoretical study of the molecular inclusion of organometallic sandwich complexes in a cavitand receptor

We describe herein a detailed study of the inclusion processes of several positively charged organometallic sandwich complexes inside the aromatic cavity of the self-folding octaamide cavitand 1. In all cases, the binding process produces aggregates with a simple 1:1 stoichiometry. The resulting inclusion complexes are not only thermodynamically stable, but also kinetically stable on the (1)H NMR spectroscopy timescale. The binding constants for the inclusion complexes were determined by different titration techniques. We have also investigated the kinetics of the binding process and the motion of the metallocenes included in the aromatic cavity of the host. Using DFT-based calculations, we have evaluated the energies of a diverse range of potential binding geometries for the complexes. We then computed the proton chemical shifts of the included guest in each one of the binding geometries. The agreement between the averaged computed values and the experimentally determined chemical shifts clearly supports the proposed binding geometries that we assigned to the inclusion complexes formed in solution. The combination of experimental and theoretical results has allowed us to elucidate the origins of the distinct features detected in the complexation process of the different guests, as well as their different motions inside the host.     

Recent developments in the application of nanoparticles prepared from w/o microemulsions in heterogeneous catalysis

This paper reviews the use of microemulsions, especially the water-in-oil (w/o) microemulsions, for preparation of nanoparticles that are employed as catalyst components in heterogeneous catalytic reactions. The objective is to show the growing interest of using microemulsions in the preparation of different types of materials such as metals, single metal oxides or mixed metal oxides with a broad range of application in heterogeneous catalysis and also in electrocatalysis. In most cases, the catalytic material showed improved catalytic properties as a result of the special synthesis environment created by the microemulsions. Still, research is needed for a better understanding of such beneficial effects. In addition, this method needs improvements in order to produce, in an environmentally friendly way, a suitable amount of material for use in industrial-scale catalytic processes.