Search results for "Virial coefficient"
showing 10 items of 44 documents
Lösungseigenschaften von äthylcellulose. Vergleichende bestimmungen von molekulargewichten und zweiten virialkoeffizienten mittels osmose, lichtstreu…
1973
Es wurden osmotische und Lichtstreuungsmessungen an Athylcellulose in Aceton, Athylacetat, Butanol-(2), n-Butylchlorid und Benzol (nur Osmose) ausgefuhrt und die Ergebnisse in einigen Fallen mit Hilfe der Sedimentation/Diffusion kontrolliert. Durch Vergleich der verschiedenen Mesmethoden konnten die von Gelen unbeeinflusten Mesergebnisse gegen die durch Gele verfalschten Werte abgegrenzt werden. Die osmotisch und hydrodynamisch bestimmten A2-Werte sind hoch im Vergleich zu denen von Vinylpolymeren. Im Gegensatz dazu steht der niedrige Exponent e der Tragheitsradius-Molekulargewichtsbeziehung der sich fur negative Exponenten e nur durch Geleinflus deuten last. fur die zweiten Virialkoeffizie…
Hydrodynamische eigenschaften von methylcellulosen in lösung
1961
Technische Methylcellulose wurde fraktioniert und auf ihr Viskositats-, Sedimentations und Diffusionsverhalten in wasriger Losung untersucht. Die Viskositats-Molekularge-wichts-Beziehung fur Methylcellulosen von etwa 28% Methoxylgehalt ergab sich zu Der Exponent 0,63 besagt, das Kette relativ eng geknauelt ist. Ihr Verhalten last sich durch die Theorien der Viskositat gut deuten. So ergibt sich nach DEBYE-BUECHE-PETERLIN fur die Knaueldimension (R = Tragheitsradius in A) was eine nur schwache Abweichung vom GAUSSschen Knauel mit M1,00 bedeutet. Das Verhalten der gelosten Methylcellulose wird zusammen mit Messungen an Athylhydroxyathylcellulosen und Cellulosenitraten betrachtet, bei denen st…
Expansionskoeffizient (α) und zweiter virialkoeffizient (A2) der lösungen von cellulosetrinitraten in aceton
1968
Durch Streulichtmessungen werden an Acetonlosungen von zwei Reihen fraktionierter Cellulosetrinitrate (CTN 13,9 und CTN 12,9 entsprechend dem %-Gehalt N) Molekulargewicht, Tragheitsradius r und 2. osmotischer Virialkoeffizient A2 gemessen. Der Expansionskoeffizient gehorcht der Gleichung α5 − α3 = 2,6 z. Sowohl z wie α sind niedrig. Thermodynamisch gibt die, h(z)-Funktion von CASASSA die Versuchsresultate am besten wieder. Die Unterschiede zwischen Losungen von Cellulosenitraten und Vinylpolymeren beruchen auf der Verschiedenheit des einzigen Parameters K0 = r/M, der bei CTN 13,9 um den Faktor 12 hoher liegt als z. B. bei Polystyrol (Tab. 8). Dadurch sind unter vergleichbaren Bedingungen in…
Interdependence of enthalpic and entropic contributions to the second osmotic virial coefficient
1972
The interdependence of the enthalpic contribution A2, H and the entropic contribution A2, s to the second osmotic virial coefficient for a given polymer-solvent system has been investigated from the experimental and the theoretical point of view. Experimentally, the following common facts were observed for various systems at temperatures and pressures below the critical values for the solvent. Both the isobaric and isothermal dependences can be approximated over relatively wide ranges of A2, H by linear relations with a slope deviating only slightly, but in a characteristic manner from a value of −1. When the temperature is increased at constant pressure one moves along an isobar towards hi…
Linear versus Three-Arm Star Polybutadiene: Effects of Polymer Architecture on the Thermodynamic Solution Behavior
2012
The interaction of linear and of three-arm star polybutadiene (PB) with THF was studied in the temperature range between 25 and 55 °C. Information for dilute solution rests on light scattering experiments; Flory–Huggins interaction parameter χ stem from vapor pressure measurements as a function of φ, the volume fraction of polymer. Despite the minute divergence in the architecture, the second osmotic virial coefficients of the two PBs differ noticeably. The present work demonstrates that these disparities become much more pronounced as φ increases and that they depend strongly on temperature. These findings are interpreted on the basis of an approach accounting for the effects of chain conn…
Chain Connectivity and Conformational Variability of Polymers: Clues to an Adequate Thermodynamic Description of Their Solutions, 1
2003
This is the first of two parts investigating the Flory-Huggins interaction parameter, χ, as a function of composition and chain length. Part 1 encompasses experimental and theorical work. The former comprise the synthesis of poly(dimethylsiloxane)s with different molar mass and the measurements of their second second osmotic virial coefficients, A 2 , in solvents of diverse quality as a function of M via light scattering and osmotic pressures. The theorical analysis is performed by subdividing the dilution process into two clearly separable steps. It yields the following expression for χ ο , the χ value in range of pair interaction : χ ο = α - ζ λ. The parameter α measures the effect of con…
Thermodiffusion anisotropy under a magnetic field in ionic liquid-based ferrofluids
2021
International audience; Ferrofluids based on maghemite nanoparticles (NPs), typically 10 nm in diameter, are dispersed in an ionic liquid (1-ethyl 3-methylimidazolium bistriflimide - EMIM-TFSI). The average interparticle interaction is found to be repulsive by small angle scattering of X-rays and of neutrons, with a second virial coefficient A2 = 7.3. A moderately concentrated sample at Φ = 5.95 vol% is probed by forced Rayleigh scattering under an applied magnetic field (up to H = 100 kA m-1) from room temperature up to T = 460 K. Irrespective of the values of H and T, the NPs in this study are always found to migrate towards the cold region. The in-field anisotropy of the mass diffusion c…
Beiträge zur polymerisation von 2-isopropenylnaphthalin, 3. Anionische homopolymerisation von 2-isopropenylnaphthalin
1981
The anionic homopolymerization of 2-isoprenylnaphthalene with butyllithium in tetrahydrofuran at –78°C is described. The refractive index increment amounts to dn/dc = 0,2084 ml/g for these polymers in toluene at 25°C and wavelength λ = 436 nm. Determination of the molecular weights by light scattering yielded values between 13 000 and 270 000. The second virial coefficients also determined by light scattering measurements are comparable with the corresponding data of poly(α-methylstyrene). A calibration curve is given for gel permeation chromatography of the poly(2-isoprenylnaphthalene)s, whose polymolecularity indexes Mw/Mn lie between 1,06 and 1,2. Their intrinsic viscosity/molecular weig…
Third virial coefficient for 4-arm and 6-arm star polymers
2008
We discuss the computation of the third virial coefficient in polymer systems, focusing on an additional contribution absent in the case of monoatomic fluids. We determine the interpenetration ratio and several quantities that involve the third virial coefficient for star polymers with 4 and 6 arms in the good-solvent regime, in the limit of a large degree of polymerization.
Association Equilibria Theory for Polymers in Mixed Solvents with Specific Interactions
2004
Hydrogen bonding plays an important role in determining the physical and thermodynamic properties of polar fluids. Theoretical and experimental aspects of polymers, in mixed solvents with hydrogen-bonding-specific interactions, are investigated using a simple association model based on the theory of association equilibria developed by Pouchly et al. The thermodynamic non-idealities are accounted for using a modified Flory-Huggins theory with effective g ij parameters. The entropic term of the above formalism has been formulated taking into account the pplymer segment-solvent as well as the solvent-solvent hydrogen-bond formation. Four equilibrium constants are introduced to make a realistic…