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Ghimici L.,Petru Poni Institute of Macromolecular Chemistry | Nichifor M.,Petru Poni Institute of Macromolecular Chemistry | Eich A.,WEE Solve GmbH | Wolf B.A.,Johannes Gutenberg University Mainz
Carbohydrate Polymers | Year: 2012

Viscosities of dilute polymer solutions were measured in capillary viscometers for samples varying in their fraction f of charged units from 0.00 to 0.90. The dependence of the logarithm of the relative viscosity on polymer concentration c is in all cases reproduced quantitatively by three characteristic parameters: [η], the intrinsic viscosity; B, a viscometric interaction parameter (related to the Huggins constant); [η], a parameter required only for polyelectrolytes at low concentrations of extra salt. In pure water [η] increases more than 80 times as the fraction f rises from zero to 0.90 and [η] starts from zero and goes up to ≈71 mL/g. Upon the addition of NaCl [η] decreases by at least one order of magnitude (depending on the value of f). The observed dependences of log [η] on log csalt can be modeled quantitatively by Boltzmann sigmoids. © 2011 Elsevier Ltd. All Rights Reserved. Source


Bercea M.,Petru Poni Institute of Macromolecular Chemistry | Nichifor M.,Petru Poni Institute of Macromolecular Chemistry | Eckelt J.,WEE Solve GmbH | Wolf B.A.,Johannes Gutenberg University Mainz
Macromolecular Chemistry and Physics | Year: 2011

The central and unexpected conclusion that can be drawn from the present work is the absence of any fundamental qualitative differences in the solution behavior of charged and uncharged polymers. For both types of systems, it is possible tomodelthethermodynamicbehaviorbythesame approach, accounting explicitly for chain connectivity and conformational relaxation. Unless very special interactions are involved (as in the case of block copolymers[14]), only three system-specific parameters are required, where it is, inmostcases, possible to eliminate one of thembymeans of the interrelation shown in Figure 15. © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim. Source


Morariu S.,Petru Poni Institute of Macromolecular Chemistry | Eckelt J.,WEE Solve GmbH | Wolf B.A.,Johannes Gutenberg University Mainz
Macromolecular Chemistry and Physics | Year: 2011

Dextran and random dextran-based copolymers containing different molar fractions f of charged units are studied in aqueous solution and in the pure state. The specific volumes of the solutions decrease linearly with increasing weight fraction of the polymer. Extrapolation to the pure state yields information on the hypothetical liquid polymers, exhibiting a pronounced minimum at f-0.1. A similar dependence is also observed for the pure solid polymers; however, the specific volumes at low f are considerably larger and at high f are slightly smaller. These differences are discussed in terms of the non-equilibrium structures formed during sample preparation. The thermal expansivities of the solutions pass through a maximum at f-0.1. Light scattering shows that the thermodynamic quality of water has a minimum at f-0.1. © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim. Source


Wolf B.A.,Johannes Gutenberg University Mainz | Wolf B.A.,WEE Solve GmbH
Industrial and Engineering Chemistry Research | Year: 2013

The thermodynamic description of the systems specified in the title requires in general dissimilar theories. This contribution presents an approach that is capable of modeling all of them with a maximum of three adjustable parameters. The Ansatz starts from the Flory-Huggins theory and extends it in a 2-fold manner: The number of segments assigned to the solvent is no longer one but treated as an adjustable parameter to account for the differences in the molecular geometries and in the free volumes of the components. Furthermore, the modeling allows for effects resulting from ternary contacts of the solvent/polymer/polymer type. Examination of the acquired thermodynamic expressions by means of literature data (composition-dependent chemical potentials of the solvents) demonstrates their validity. Solutions of proteins and of linear or branched chainlike macromolecules require two adjustable parameters for the quantitative thermodynamic modeling; polyelectrolyte solutions necessitate a third one. © 2013 American Chemical Society. Source


Bercea M.,Petru Poni Institute of Macromolecular Chemistry | Nita L.-E.,Petru Poni Institute of Macromolecular Chemistry | Eckelt J.,WEE Solve GmbH | Wolf B.A.,Johannes Gutenberg University Mainz
Macromolecular Chemistry and Physics | Year: 2012

In contrast to all earlier work on that subject, measurements are performed at high dilution up to total polymer concentrations wpol of 0.5 wt%. Aqueous solutions of poly(2-vinylpyrid-inium-Br) and of poly(styrene sulfonate-Na) are only fully miscible if wpol < 0.02 wt%. Decomposition into two liquid phases is observed upon an increase in wpol, where the extension of the miscibility gap is considerably larger at 60 than at 25 °C. Viscosity measurements demonstrate that the formation of the polyelectrolyte complexes may take hours. The intrinsic viscosity of the polyanion turns out to be 20 times larger than that of the polycation and to be much more sensitive toward the addition of extra salt. The [η] values of the blend pass a minimum as a function of its composition. © 2012 WILEY-VCH Verlag GmbH & Co. KGaA. Source

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