Spontaneous Interfacial Tension Changes at the Interface of Metal Chloride Nitrobenzene Solution and Aqueous Stearyltrimethylammonium Chloride Solution: the Role of Metal Ions

Abstract

The authors examine the roles of chemical compounds that can generate spontaneous interface motion, especially in the Nakache and Dupeyrat system, which normally uses a stearyltrimethylammonium chloride (STA-Cl) aqueous solution and a KI + I2 nitrobenzene solution. The authors observed spontaneous behavior at the interface of a system comprising the STA-Cl aqueous solution and a nitrobenzene solution of ZnCl2 or FeCl3. To investigate the role of metal ions, in-situ electrochemical measurements of systems of various metal halides, such as KCl, CaCl2, AlCl3, ZnCl2, and FeCl3, were conducted and discussed regarding the relationship of the spontaneous interface motion with the consideration of standard Gibbs energy of surfactant adsorption, solubility into the oil phase, and hydration enthalpy. The importance of electric potential dependence of surfactant adsorption–desorption at the oil/water interface is suggested and supported using an FeCl3 chlorobenzene solution. A material design with the consideration of a potential barrier of surfactant desorption would enable us to obtain a spontaneous motion system not utilizing toxic substances.