STUDIES OF POLYELECTROLYTE SOLUTIONS .4. EFFECTS OF IONIC-STRENGTH ON THE EFFECTIVE POLYION CHARGE

Autor(en): NORDMEIER, E
Stichwörter: CONDENSATION; DILUTE-SOLUTIONS; DOUBLE-LAYER; DYNAMIC LIGHT-SCATTERING; EFFECTIVE POLYION CHARGE; ELECTROLYTES; FD-VIRUS; FILAMENTS; HYDRODYNAMIC RADIUS; POLY(STYRENE SULFONATE); Polymer Science; QUASI-ELASTIC LIGHT SCATTERING; SEMIDILUTE REGIMES; SPECTRUM; SUSPENSIONS; TRANSLATIONAL DIFFUSION COEFFICIENT
Erscheinungsdatum: 1993
Herausgeber: SOC POLYMER SCIENCE JAPAN
Journal: POLYMER JOURNAL
Volumen: 25
Ausgabe: 1
Startseite: 19
Seitenende: 30
Zusammenfassung: 
Quasi-Elastic light scattering experiments have been performed on aqueous solutions of sodium poly(styrene sulfonate) (M(w) = 3.5 x 10(5) g mol-1) in the ionic strength range of 0.005 to 2M at T = 20-degrees-C. The angular dependence of the apparent diffusion coefficient was analyzed within the framework of the Fujime-Maeda theory for semiflexible rods. At zero polyion concentration both the overall translational and the rotational diffusion coefficient increase with the ionic strength, while the difference between the translational diffusion coefficients perpendicular and parallel to the rod axis decreases. The molecular structure of a PSS-polyion is also quite well described by the model of a wormlike prolate ellipsoid, where the ratio of the minor to the major semiaxis rises from 0.29 at low ionic strength (I = 0.005 M) to 1 at the theta-state. By solving the Poisson-Boltzmann equation we have determined the effective polyion charge, Z(eff), that is not neutralized by the small ions at a distance r = d(h)/2 from the PSS-skeleton, where d(h) is the hydrodynamic diameter of the polyion. It is found: (1) Z(eff) is independent of the ionic strength; and (2) Z(eff) is much smaller than the corresponding Z-values obtained from dialysis equilibrium experiments. The reason for this discrepancy is clear. The dialysis technique yields the surface charge of the polyion, while transport techniques such as diffusion experiments yield the effective charge, Z(eff). The latter incorporate hydrodynamic and electrostatic coupling forces acting between the polyion and the associated ion cloud, while the former do not.
ISSN: 00323896
DOI: 10.1295/polymj.25.19

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