über den Temperaturkoeffizienten der Viskosität von Flüssigkeiten im Zusammenhang mit der Struktur von Kautschuk in Lösung

Colloid and Polymer Science -     

Die Untersuchung des Pfeffers

Ohne Zusammenfassung     

Concentration effects on the dynamics of liquid crystalline self-assembly: time-resolved X-ray scattering studies

A manifold of ordering transitions relevant to chemical and biological systems occur at interfaces from liquids to self-assembled soft solids like membranes or liquid crystals. In the present case, we were interested in understanding the phase transition from the microemulsion phase to the liquid crystal phase in terms of their driving forces, i.e., activation energy and entropy. The purpose of this work was to clarify the influence of concentration effects of the amphiphilic molecules on the nature of these self-assembly processes. By photosensitization of the model system (polyalkylglycolether (C(10)E(4)), water, decane, and cyclohexane) with laser dyes, we could effectively induce and control the phase transition through the absorption of optical photons. The photo transformation conditions were chosen in such a way that the system was in thermal equilibrium. By application of time-resolved photo small-angle X-ray scattering we could monitor the conversion process and demonstrate that the surfactant concentration has a direct impact on the activation energy, which is observable through the length of the induction time.     

Instabilities of longitudinal convection rolls in couette flow

Summary An investigation has been made of the instabilities of longitudinal convection rolls in a Couette flow which is heated from below. The instabilities occur either as stationary waves or as waves which propagate along the convection rolls. Neutral stability curves are presented as a function of Rayleigh and Reynolds numbers for a Prandtl number of 0.7. The disturbance energy budget is given for selected values of the Rayleigh and Reynolds numbers.

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Zusammenfassung Die Instabilitäten von longitudinalen Konvektionsrollen in einer ebenen Couette-Strömung, die von unten erhitzt wird, sind untersucht worden. Die Instabilitäten nehmen entweder die Form von stehenden Wellen an oder von Wellen, die sich entlang der Konvektionsrollen fortpflanzen. Die Kurven für marginale Stabilität sind als Funktion der Rayleigh-und Reynoldszahl dargestellt worden im Fall der Prandtlzahl 0.7. Das Energiebudget der Störungen wird für ausgewählte Werte der Rayleigh-und Reynoldszahl angegeben.

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Dedicated to Professor Nikolaus Rott on the occasion of his 60th birthday.     

Large wavelength convection rolls in low Prandtl number fluids

Summary By extending the parameter range of the previous numerical stability analysis of convection rolls (Clever and Busse, 1974) a new instability has been found. In low Prandtl number fluids this instability, called the skewed varicose instability, causes an increase of the wavelength of convection rolls with increasing Rayleigh number. A comparison between theoretical results and experimental observations shows good agreement.

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Zusammenfassung Bei einer Erweiterung des Parameterbereichs der früheren numerischen Stabilitätsanalyse von Konvektionsrollen (Clever und Busse, 1974) ist ein neue Instabilität gefunden worden. In Fluiden mit niedriger Prandtl-Zahl bewirkt diese Instabilität, die skewed varicose Instabilität genannt wird, eine Vergrösserung der Wellenlänge der Konvektionsrollen, wenn die Rayleigh-Zahl zunimmt. Ein Vergleich zwischen theoretischen Resultaten und experimentellen Beobachtungen zeigt gute Übereinstimmung.

     

Mechanical structures in polymer melts. I. Measurements of melt strength and elasticity

The standard methods of measuring the elastic properties of polymer melts are briefly reviewed and a method of measuring another combination of viscoelastic properties, the melt strength, is described. Data are presented on the melt strength of various types of polyethylene resins and on ionomer resins. The effects on various viscoelastic properties of branching or of the addition of fine fibrils of Teflon perfluorocarbon resin are reported.