Bestimmung der Langkettenverzweigung von Hochdruckpolylithylen durch Streulicht- und Viskosit?tsmessungen

Ohne Zusammenfassung     

Schnelle Dichtegradienten-Zentrifugation dispergierter Teilchen

Zusammenfassung Zur Untersuchung der chemischen Zusammensetzung dispergierter Teilchen, z. B. in Polymerlatices, wird eine schnelle Methode der Dichtegradienten-Zentrifugation entwickelt. Mit ihr kann die Verteilung der Dichte und damit der chemischen Zusammensetzung der Teilchen in wenigen Minuten bestimmt werden. Die bisher dafür verwendete konventionelle Dichtegradienten-Zentrifugation erfordert Versuchszeiten von 15 bis 30 Stunden.Das Prinzip der schnellen Methode beruht auf der Überschichtung von chemisch weitgehend gleichen oder ähnlichen Dispersionsmitteln unterschiedlicher Dichte (z. B. H₂O und D₂O oder Buten-(3)-ol-(2) und Ethylenglykol) und der Einstellung des Dichtegradienten durch Diffusion. Hauptanwendungsgebiete sind die Ermittlung der chemischen Zusammensetzung und Uneinheitlichkeit von Co-, Pfropf- und Mischpolymerlatices und die Bestimmung von Teilchenvernetzungsgraden.

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Summary For the investigation of the chemical composition of dispersed particles, e. g. in polymer latices, a rapid method of density gradient centrifugation is developed. The method yields in a few minutes the density distribution and by this the distribution of the chemical composition of the particles. The standard density gradient centrifugation needs for the same results more than 15 hours.The rapid method is based on adding a layer of a dispersion medium of low density to a chemically similar medium of high density (e. g. H₂O to D₂O or 3-butene-2-ol to ethylene glycol) and forming the density gradient by diffusion. The main field of application is the investigation of the chemical composition and heterogeneity of copolymer latices and latex mixtures and of the particle cross linking.

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Mit 10 Abbildungen und 2 Tabellen     

Dispersion in annular climbing film flow

The dispersion of a tracer injected as a pulse into a climbing liquid film is investigated for a series of water and air flow rates, and for a number of different electrolyte tracers. It is found that at all flow rates the observed concentration distribution depends on the nature of the tracer. This observation is explained in terms of two effects: molecular diffusion in a viscous sub-layer and ion fractionation associated with droplet formation at the gas-liquid interface. The overall dispersive characteristics of the system are described in terms of a mathematical model assuming dispersed plug flow in both the film and entrained droplets with interchange between these phases. This model is fitted to experimental tracer concentration distributions using a non-linear least-squares regression procedure. The parameter values obtained from the fitting procedure are studied to determine trends with flow rates and tracer properties. Values for a film dispersion parameter, $\text{P}{}_{\mathrm{f}}$, are found to correlate significantly with the molecular diffusion coefficients of the tracers. Consistent values for an ion fractionation coefficient, $\text{k}{}_{\mathrm{if}}$, are also obtained.     

A simple method of observing coherent ground state transients

It is shown that coherence between nondegenerate sublevels of an atomic ground state is efficiently induced by means of a short resonant light pulse. The free precession of the coherence causes beats in forward stattering of a probe beam, which can sensitively be detected by a polarization technique. Zeeman beats on the 4f⁶ 6s²⁷ F₁-4f⁶ 6s6p ⁷F₀ transition of samarium were observed. In sodium vapor transient ground state coherence was detected in a single-shot measurement.