Search results for "VISCOSITY"
showing 10 items of 542 documents
Die molekularen Konstanten von Polycarbonaten in Lösung
1959
An einer Reihe von fraktionierten Polycarbonaten werden in zwei Losungsmitteln die Diffusions- und Sedimentationskonstanten, die Viskositatszahlen, die osmotischen Drucke sowic die Lichtstreuung gemessen. Daraus wird eine Eichkurve zur viskosimetrischen Molekulargewichtsbestimmung abgeleitet und aus einem Vergleich der verschidednen Mittelwerte des Molekulargewichts die Uneinheitlichkeit der Fraktionen abgeschatzt. Aus den Reibungs-und Lichtstreuungsdaten werden die Knauelabmessungen berchnot und mit Hilfe der gemessenen zweiten Virialkoeffizientin auf das indifferente Losunmittal reduziert. Die Volumbeanspruchung der Polycarbonatmolekule in Losung ist groser als die vergleichbarer Polyviny…
Vorschlag zur Unterscheidung der 2 Größen: „Grenzviskositätszahl” u. „konventionelle Viskositätszahl”
1954
Fur viskosimetrische Molekulargewichtsbestimmungen ist es nicht notig, die Viskositatszahl auf den Geschwindigkeitsgradienten 0 zu extrapolieren. Es wird empfohlen, die Viskositatszahl derart zu normieren, das zur Messung bestimmte Kapillarenradien verwendet werden. Dadurch wird jedem Losungsmittel ein bestimmter Gradient (i. A. zwischen 0,5 und 1,5.103 sec−1 zugeordnet, und damit ist auch fur jedes in diesem Losungsmittel gemessene Polymere die „konventionelle Viskositatszahl” eindeutig und reproduzierbar festgelegt. Eichkurven zur viskosimetrischen Molekulargewichtsbestimmung sollten auf die konventionelle Viskositatszahl bezogen werden. Diese weicht nur bei hohen Polymeren von der Grenzv…
Molekulargewichtsbestimmungen an verschieden scharf fraktionierten polymethacrylsäuremethylestern
1954
Aus drei Polymethacrylsauremethylestern, deren Molekulargewichte bei ungefahr 35 000, 500 000 und 8 000 000 lagen, wurden durch fortgesetzte Fraktionierung Praparate von sehr verschiedener Einheitlichkeit hergestellt. Das Molekulargewicht der einzelnen Fraktionen wurde in der Ultrazentrifuge gemessen, sowie die zugehorige Viskositatszahl in Benzol bestimmt. Es zeigt sich, das der Einflus der Einheitlichkeit fur die Beziehung zwischen Polymerisationsgrades und Viskositatszahl gering ist, falls man den Gewichtsdurchschnitt des Molekulargewichtes mist. Die bei diesen Versuchen gewonnenen Sedimentations- und Diffusionskurven werden im Hinblick auf die aus ihnen zu berechnenden Verteilungskurven…
Preliminary evaluation of durum wheat (Triticum Turgidum Subsp Durum) during malting process:
2018
Durum (T. turgidum subsp. durum) wheat production worldwide is substantially less than that of common wheat (Triticum aestivum) mainly due to the relatively limited end-users. In order to evaluate malting and brewing suitability, sixteen old durum wheat landraces were malted at micro scale. Results show malt quality parameters in the range 78.2–85.9% for the extract, 72.9–80.9% for the fermentability, 3–5 EBC units for the colour, 0.49–0.79% dm for water-extractable arabinoxylans and 0.043–0.059% dm for the β-glucans. Regarding wort viscosity (1.53–1.92 mPa s), we found negative correlation with endo-1,4-β-D-xylanase, positive correlation with endo-β-glucanases and soluble proteins, while n…
Rotation correlation time as a measure of microviscosity of excited state isomerization reactions of three cyanine dyes in n-alcohol solutions
1994
Abstract Rotation correlation times of three chemically similar cyanine dyes of different sizes in n -alcohol solutions have been recorded at several temperatures by using polarized picosecond spectroscopy. For all three dyes the linear temperature dependencies of τ or on η/ T were observed to be independent of solvent up to viscosities of about 60 cP. The rotational motion of the dyes proceeds at much slower rates than the excited state isomerization in viscous solutions of the same fluidity. Isomerization seems to depend on special solvent-induced changes of the force field of the reactant and clearly proceeds faster, especially for the two larger dyes, than predicted by Kramers' theory a…
CHLOROPHYLL a AGGREGATES IN HYDROCARBON SOLUTION, A PICOSECOND SPECTROSCOPY AND MOLECULAR MODELING STUDY
1993
Chlorophyll a aggregates in 3-methylpentane solution have been studied by using picosecond absorption and fluorescence spectroscopy and molecular modeling. Chlorophyll a aggregates give rise to reversible temperature changes in the absorption and fluorescence spectra. Time-dependent anisotropies were used to estimate rotational correlation times of the aggregates. These were indicative of the sizes of the aggregates. The rotational diffusion of the monomer and the two identified aggregates was hydrodynamic over the viscosity range studied (0.29–1.8 cP). Molecular mechanics calculations were used to predict the minimum energy structures of several chlorophyll a dimers suggested earlier in th…
Behavior of Flavor Compounds in Model Food Systems: a Thermodynamic Study
2003
Physicochemical parameters, such as hydrophobicity, water solubility, and volatility, of four flavor compounds (ethyl acetate, ethyl butyrate, ethyl hexanoate, and 2-pentanone) were determined. The amount of flavor compounds released from different model matrices (mineral water, purified triolein, an oil-in-water emulsion, a carbohydrate matrix, and a complex matrix containing lipids and carbohydrates) into the gaseous phase was determined at thermodynamic equilibrium, at 37 degrees C, by static headspace gas chromatography. The degree of interaction between the flavor compounds and the matrix components was shown by measuring the percentage retention using the water matrix as the reference…
Densities, Viscosities, and Refractive Indices of Some Binary Liquid Systems of Methanol + Isomers of Hexanol at 298.15 K
1996
Viscosities, densities, and refractive indices of eight binary liquid systems containing ethanol + some isomers of hexanol have been determined at 298.15 K. The excess property values were fitted to the Redlich-Kister equation to estimate the binary coefficients and the standard deviations.
Influence of impregnation solution viscosity and osmolarity on solute uptake during vacuum impregnation of apple cubes (var. Granny Smith)
2008
Vacuum-assisted impregnation of pectinmethylesterase (PME) solution has been recognized as an efficient pretreatment to improve the firmness of heat-treated fruit. In order to improve the control of solute infusion into fruit pieces, the effect of the osmolarity and viscosity of vacuum impregnation solution on solute penetration and distribution was studied in 1.5 cm apple cubes, using model PME-based solutions containing sodium chloride and/or sodium alginate. While vacuum impregnation of either a viscous hypotonic or a non-viscous hypertonic solution infused solutes homogeneously into fruit pieces, the penetration of viscous hypertonic solutions was much lower, and PME or chloride infusio…
Preferential solvation of a dicyanate ester monomer and poly(sulfone) in different organic solvents by size-exclusion chromatography.
2002
Preferential solvation parameters A in the ternary systems solvent (1) -monomer (2) -polymer (3) were determined as a tool to measure the compatibility between the cyanate ester monomer Arocy B10 and poly(sulfone), PSF, in the presence of three organic solvents: tetrahydrofuran, dimethylformamide and dicloromethane. The A parameter was measured by size-exclusion chromatography at different monomer-to-polymer ratios. The quantitative evaluation was rigorously made at polymer-diluted conditions. PSF was found to be preferentially solvated by the monomer. Concerning the solvent used, systems containing tetrahydrofuran showed the strongest solvation, the lowest A values being those obtained in …