Analytical Sciences

Chemical Oscillation with Periodic Adsorption and Desorption of Surfactant Ions at a Water/Nitrobenzene Interface

Yasuhiro IKEZOE,*¹ Sadahiro ISHIZAKI,*¹ Hiroharu YUI,*^1,*² Masanori FUJINAMI,*^1,*³ and Tsuguo SAWADA*^2,*⁴

*1 Department of Advanced Materials Science, Graduate School of Frontier Sciences, The University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa, Chiba 277-8561, Japan
*2 Core Research for Evolutional Science and Technology (CREST), Japan Science and Technology Agency (JST), 5-1-5 Kashiwanoha, Kashiwa, Chiba 277-8561, Japan
*3 Department of Applied Chemistry & Biotechnology, Chiba University, 1-33 Yayoi, Inage, Chiba 263-8522, Japan
*4 Department of Chemical Engineering, Tokyo University of Agriculture and Technology, 2-24-16 Naka-cho, Koganei-city, Tokyo 184-8588, Japan

Chemical oscillations with periodic adsorption and desorption of surfactant ions, alkyl sulfate ions, at a water/nitrobenzene interface have been investigated. The interfacial tension was measured with a quasi elastic laser scattering (QELS) method and the interfacial electrical potential was obtained. We found that this oscillation consists of a series of abrupt adsorptions of ions, followed by a gradual desorption. In addition, we observed that each abrupt adsorption was always accompanied by a small waving motion of the liquid interface. From the analysis of the video images of the liquid interface or bulk phase, we could conclude that each abrupt adsorption is caused by nonlinear amplification of mass transfer of ions from the bulk phase to the liquid interface by a Marangoni convection, which was generated due to local adsorption of the surfactant ions at the liquid interface that resulted in the heterogeneity of the interfacial tension. In the present paper, we describe the mechanism of the chemical oscillation in terms of the hydrodynamic effect on the ion adsorption processes, and we also show the interfacial chemical reaction with ion exchange during the ion desorption process.

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