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Effect of adsorption, ionic strength and pH on the potential of the diffuse electric layer

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Zusammenfassung

Das Potentialϕ 0 der diffusen elektrischen Doppelschicht wurde nach der Methode des flüssigen Gleichgewichtfilms in Schäumen (1) bestimmt. Die Dicke der Filme wurde interferometrisch (7, 8) gemessen.

Es wurde die Abhängigkeit desϕ 0-Potentials von der KonzentrationC S des grenzflächenaktiven Stoffes (Schaumfilmstabilisator) untersucht. Dieϕ 0 (C S)-Kurve hat am Anfang ein kleines Plateau, danach folgt ein Anstieg bis zu einem Sättigungswert. Dieser Sättigungswertϕ 0∞ ist für die verschiedenen Tenside unterschiedlich. Nichtionogene Tenside besitzen ein geringesϕ 0∞, die ionogenen Tenside geben höhere Werte.

Es wurde weiterhin der Einfluß der Elektrolytkonzentration auf dasϕ 0-Potential untersucht. Eine spezifische Wirkung der Elektrolyte wurde nicht gefunden. Dagegen wurde ein starker Einfluß des pH-Wertes auf dasϕ 0-Potential festgestellt. Bei einem bestimmten pH-Wert fälltϕ 0 bis zu Null ab, d. h. ein isoelektrischer Punkt tritt auf. Die an Schaumfilmen gemessenenϕ 0-Werte wurden mit denϕ 0-Werten an der Oberfläche derselben Lösung verglichen.

Summary

The potential,ϕ 0, of the diffuse electric layer was determined by the equilibrium liquid film method (1). The method is based on calculating theϕ 0-potential by means of the DLVO theory of the electrostatic disjoining pressure at known concentration,C el of the solution forming the microscopic liquid film and at known thickness,h r of the film. The thickness of the film was measured by the microinterferometric method (7, 8). The calculation of the potential was carrried out by means of the more general eqs. [2] and [3], valid for a wide range ofC el andϕ 0. The dependence of the potential of the diffuse electric layer on the concentration of surface activ agent (surfactant) stabilizing the liquid film was found. It was established that ionogenic SAS show a higher potential than the non-ionogenic ones. The potential of SAS-free solutions was determined — ca. 30 mV.

The dependence of the potential of the diffuse electric layer on concentration and kind of electrolyte was also found.

A strong effect of pH onϕ 0-potential was observed and the isoelectric points were found. An analysis is made of theϕ 0-potential values obtained by the method of equilibrium liquid film with respect to their similarity to those on the boundary of the bulk liquid.

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  1. D. Exerowa

    Present address: Bulgarian Academy of Sciences, Institute of Physical Chemistry, Sofia, Bulgaria

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    Exerowa, D. Effect of adsorption, ionic strength and pH on the potential of the diffuse electric layer. Kolloid-Z.u.Z.Polymere 232, 703–710 (1969). https://doi.org/10.1007/BF01500168

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