THE INFLUENCE OF THE FILM CONTACT ANGLE OF EMULSION DROPLETS ON THE DISPERSIBILITY OF THEIR SEDIMENTS.

In certain W/0 emulsions, the films between the flocculated water droplets and the adjoining menisci show a very large contact angle θ. Because this phenomenon indicates a strong interaction of the droplets, we investigated its influence on the redispersion of sediments formed in such emulsions.

Two models describing the yield stress of such sediments were developed using calculations that relate the yield stress of a string of emulsion droplets to the value of θ. The first model estimates the maximum yield stress that can be accounted for by capillary forces. The second model considers the yield stress of sediments consisting of droplet aggregates joined by single chains of droplets.

These theories were found to describe satisfactorily cone penetration and redispersion experiments performed on two series of W/O emulsions that exhibited a wide range of values of Θ.     

Paramagnetic oxygen centres in SrTiO3 induced by light

The ESR spectra of two light-induced defect centres in annealed SrTiO₃ single crystals are reported and ascribed to O^3?₂. In crystals treated in a water vapour at high temperature a third light-induced centre was found, assigned to O^?.     

Vibrational relaxation and intermediate strong coupling

In this paper the effect of collisions with inert gas molecules upon the intermediate strong coupling situation, found in the fluorescence of isolated pyrene molecules after pulse laser excitation in the S₀ → S₃ absorption band, is studied.     

SCF Cl calculations and assignment of the S1 → Sn absorption spectra of 1,1′-binaphthyl in different molecular conformations

An SCF calculation followed by extensive configuration interaction between all singly-excited singlet states has been performed for 1,1′-binaphthyl as a function of the dihedral angle. With these results an assignment of the electronic absorption bands in rigid and in fluid solution is given.     

Photo-ionization of aromatic hydrocarbons in boric acid glasses

We show here that the Hamiltonian for an electronic system may be written exactly in terms of fluctuation operators that transition constituent fragments between internally correlated states, accounting rigorously for inter-fragment electron exchange and charge transfer. Familiar electronic structure approaches can be applied to the renormalised Hamiltonian. For efficiency, the basis for each fragment can be truncated, removing high-energy local arrangements of electrons from consideration, and effectively defining collective coordinates for the fragments. For a large number of problems (especially for non-covalently interacting fragments), this has the potential to fold the majority of electron correlation into the effective Hamiltonian, and it should provide a robust approach to incorporating difficult electronic structure problems into large systems. The number of terms in the exactly transformed Hamiltonian formally scales quartically with system size, but this can be reduced to quadratic in the mesoscopic regime, to within an arbitrary error tolerance. Finally, all but a linear-scaling number of these terms may be efficiently decomposed in terms of electrostatic interactions between a linear-scaling number of pre-computed transition densities. In a companion article, this formalism is applied to an excitonic variant of coupled-cluster theory.     

Der Einfluß der Wechselwirkungskräfte zwischen Festkörpern auf deren Haftfestigkeit

Zusammenfassung Die Adhäsionsarbeit kennzeichnet den Einfluß der Wechselwirkungskräfte zwischen Festkörpern auf die Haftfestigkeit.Bei langsamer Trennung der haftenden Körper entspricht diese Adhäsionsarbeit der Differenz zwischen der Grenzflächenspannung der Haftfläche und der der getrennten Körper.Experimentell sind nur Abänderungen der Grenzflächenspannung von Festkörpern zugängig, z. B. mittels Messungen von Kontaktwinkeln oder von Adsorptionsisothermen. Es zeigt sich, daß die aus solchen Messungen errechneten Abänderungen der Grenzflächenspannung mit gemessenen Abänderungen der Haftfestigkeit im Einklang sind. Bei schneller Trennung der Körper übersteigt die Haftkraft den thermodynamischen Erwartungswert. Abschäztung der Adhäsionsarbeit muß dann mittels physikalischer Modelle der Wechselwirkungsenergie erfolgen.

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Summary The influence of the forces of interaction between solids on their adhesive strength is characterized by the work of adhesion. If the adhering solids are slowly separated, the work of adhesion is equal to the difference between the interfacial tension of the adhering surfaces and that of the separated solid bodies. Only changes in the interfacial tension of solids can be determined experimentally, e. g. by measuring contact angles or adsorption isotherms. It appears that the changes in interfacial tension calculated from these measurements are in agreement with the measured changes in adhesive strength.In the case of rapid separation of the solid bodies, the adhesive force exceeds its expected thermodynamic value. The work of adhesion must then be estimated by means of physical models of the force of interaction.

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Mit 12 Abbildungen und 1 Tabelle

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Vortrag vor der VDI Gesellschaft für Verfahrenstechnik und Chemieingenieurwesen am 20. Oktober 1976 in Oberursel.     

Vibrational redistribution effects in the time resolved emission of isolated pyrene molecules

Arguments are given that the appearance of a short component in the fluorescence decay of pyrene after excitation in a vibronic origin of the S₀ → S₁ transition, has to be ascribed to a redistribution of vibrational energy of the inducing mode over the other vibrational modes in the molecule.