Abstract
The ion-dependency of oscillatory wetting under a DC voltage, which had been reported previously, was studied in detail. The oil and water phases contained anionic and cationic surfactants, respectively. The contact line of the oil/water interface and the glass surface exhibited a successive pulsation under a DC voltage. This oscillatory wetting occurred for a Ba2+-containing system and was suppressed by Ca2+. The mechanism for the ion dependency was examined in detail. The frequency of the pulsation showed a sudden change at a threshold molar ratio of [Ca2+]/([Ca2+]+[Ba2+]). When water containing Ca2+ was injected into the Ba2+-containing interface, a significant time was required to stop the pulsation. The addition of Ba2+ into the Ca2+-containing interface instantaneously activated the pulsation even when Ca2+ had been dissolved in the water phase. The dynamic behavior was explained in terms of an interfacial chemical reaction with complex formation between the cations and the anionic surfactant.
