Electrocapillary phenomena at oil-water interfaces

Summary The electrocapillary phenomena at oil-water interfaces, i. e. the change in the interfacial tension with an applied potential difference, take place over a moderate polarization range of ca. 20 to –20 V, when the systems have sufficiently high electric conductance and contain surface active agents. Experiments were carried out in the presence of potassium chloride in the aqueous phase and ionic surface active agents in the oil phase, respectively. It was found that the interfacial tension was suppressed over the cathodic or anodic polarization range, depending on whether the surface active agent used was cationic or anionic, respectively. Here the sign of polarization was conventionally taken as that of the water phase with respect to the oil phase. It was then concluded by the use of theLippmann-Helmholtz equation that the water side of the interface is charged positively or negatively in the respective case mentioned above. It appears that this charge is due to the counter ion layer which is formed corresponding to the adsorption of ionic surface active agents on the oil side.

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Zusammenfassung Die Elektrokapillarität von Öl-Wasser-Grenzflächen mit Kaliumchlorid in den wässerigen und grenzflächenaktiven Ionen in der Ölphase wurde bei geringer Polarisation im Bereich von +20 V bis –20 V untersucht. Dabei wurde beobachtet, daß die Grenzflächenspannung durch kationische bzw. anionische Polarisation erniedrigt wurde, je nachdem, ob die grenzflächenaktiven Stoffe kationisch oder anionisch waren. Die Ergebnisse wurden mit Hilfe derLippmann-Helmholtz-Gleichung gedeutet. Es bildet sich eine elektrische Doppelschicht mit den grenzflächenaktiven Ionen an der Ölschicht und den anorganischen Gegenionen an der wässerigen Seite der Grenzfläche.

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With 10 figures and 2 tables     

The coalescence of mercury droplets in aqueous solutions in the presence of surface active materials

Colloid and Polymer Science - The range of the electrical potential of coalescence of mercury droplets in solutions of surface active materials was measured by using the twin dropping mercury...     

Electrocapillary phenomena at oil-water interfaces

Summary The interfacial tension, between the oil phase containing an ionic surface active agent and the aqueous phase containing an inorganic electrolyte, is a function of the potential difference applied to the two phases from an outer circuit. This phenomenon, the electrocapillarity at oil-water interfaces, was used by the present authors to study the structure of electrical double layers and the interaction between surface active agent ions and counterions. In the present study an amphoteric material, the lecithin, was used as the surface active agent, and its adsorption and dissociation behaviours as well as its interaction with counterions were examined. It was found that the lecithin dissolved in the oil phase behaved as the cationic or anionic surface active agent according as the p_H of the aqueous phase was acidic or alkaline. This showed that the ionic groups of the lecithin molecule are immersed into the aqueous side of the interface. Since the interfacial tension was independent of the applied potential at the interfacial isoelectric point, this point could be measured with a high sensitivity. The ionic species of the inorganic electrolyte in the aqueous phase had a marked influence on the isoelectric point. The reversal of charge spectra thus obtained were found to agree fairly well with that obtained by other authors using electrophoretic measurement.With 12 figures