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61.
H. Lange 《Colloid and polymer science》1980,258(9):1077-1085
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.
Mit 10 Abbildungen und 2 Tabellen 相似文献
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.
Mit 10 Abbildungen und 2 Tabellen 相似文献
62.
A. Roukens de Lange 《International Journal of Multiphase Flow》1979,5(1):59-78
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, , are found to correlate significantly with the molecular diffusion coefficients of the tracers. Consistent values for an ion fractionation coefficient, , are also obtained. 相似文献
63.
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. 相似文献
64.
65.
Niels Olaf Østerberg Torben Smith Sørensen Jørgen Birger Jensen 《Journal of Electroanalytical Chemistry》1981,119(1):93-108
The emf of electrochemical cells containing various sorts of salt bridges between various concentrations has been measured. The net diffusion potential over a salt bridge has been treated theoretically. An expression to calculate the net diffusion potential has been derived and tested on values estimated from the emf measurements. A merit factor has been calculated for a saturated KCl bridge separating two HCl solutions and compared with the merit factor estimated from emf measurements on the cell:Pt|Ag|AgCl, HCl(c1)|KCl(sat)|HCl(c2), AgCl|Ag|Pt The practical performance of two commonly used reference electrodes with salt bridges has been tested on emf measurements on KBr solutions. 相似文献
66.
67.
Loutelier-Bourhis C Legros H Bonnet JJ Costentin J Lange CM 《Rapid communications in mass spectrometry : RCM》2004,18(5):571-576
The ex vivo identification of dopaminergic metabolites present in rat striata after (L-DOPA + benserazide) treatment is reported. The different metabolites have been identified as the trimethylsilyl derivatives in the striatal extracts by gas chromatography/mass spectrometry. 相似文献
68.
We report observation of the interaction between two coherent dissipative spatial solitons in a periodically patterned semiconductor optical amplifier with power levels of tens of milliwatts. The interactions are nonlocal and phase dependent and exhibit surprising features, such as soliton birth. The experimental results are in good agreement with the numerical simulations. 相似文献
69.
J.?Philip J.P.?Sprengers P.?Cacciani C.A.?de Lange W.?UbachsEmail author 《Applied physics. B, Lasers and optics》2004,78(6):737-743
Tunable narrowband extreme ultraviolet radiation in the range 91–95 nm is produced by sum-frequency mixing of the outputs of a visible pulsed dye amplifier (seeded by a ring dye laser) and of a seeded second-harmonic Nd:YAG laser and subsequent frequency tripling in a gas jet of xenon. The capability of this scheme to provide tunable narrowband extreme ultraviolet radiation is demonstrated in several spectroscopic studies. The bandwidth of this system (0.01 cm-1) is deduced from a recording of absorption spectra of the 4p5(2P1/2)6d, J=1 line in krypton. The applicability of the system for gas-phase molecular spectroscopic studies is demonstrated in recordings of the Werner bands (4,0) in H2 and (5,0) in D2 at unprecedented absolute accuracy. Line-broadening studies are performed on the b1u+,v=5 valence state in N2, yielding a lifetime of 210±25 ps. A singlet–triplet perturbation, giving rise to an accidental predissociation in an excited 1 Rydberg state in carbon monoxide at an excitation energy of 107680 cm-1, is analyzed in high resolution. PACS 42.65.Ky; 32.80.Rm; 33.20.Ni; 33.80.Gj; 42.60.By 相似文献