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Synergetics pp 156-160 | Cite as

Sur l’origine d’instabilités chimiques et hydrodynamiques observées à l’interface huile-eau

  • M. Dupeyrat
  • E. Nakache
Conference paper
  • 226 Downloads
Part of the Springer Series in Synergetics book series (SSSYN, volume 3)

Abstract

The instabilities at various oil-water interfaces we have studied appear as an interfacial turbulence related to local variation of the interfacial tension; they belong to Narangoni effects. The motion observed occurs between two immiscible solutions’ containing charged species, one of which is surface active. It can only be observed when two ionic compounds are present, one in each phase, in concentrations far from equilibrium, for instance hexadecyltrimethylammonium chloride (C16Cl), a compound which is hydrophobic, dissolved in water, and picric acid (HPi), a hydro-philic substance, dissolved in nitro ethane.

The motion appears under two different forms, as shall be shown in a film, according as the interface is in contact or not with a glass wall. In the first case, a motion of the interface arises along the wall, as a wave about 1 cm. amplitude, first deforming the meniscus, then stirring the whole interface. In the second case, local contractions or expansions in the interface plane can be observed. This latter Kind of motion which involves less complex processes will be only studied.

Recent experiments have shown that the determining factor of the motion seems to be neither the mass transfer, nor the heat transfer. A chemical reaction seems to be necessary. Now a very simple acido-basic reaction, involving HPi and C16Cl for instance should be sufficient to start the motion.

SANFELD et al. studying theoretically the hydrodynamical stability of a plane interface where interfacial chemical reactions and matter transfer take place, showed that when an interfacial reaction involves one fluctuating species only, an instable reaction is a necessary but not sufficient condition to deform the interface.

We propose a mechanism of transfer involving a chemical oscillating reaction, which could explain the phenomenon observed. The interpretation is supported by two experimental observations.
  • The variation of the interfacial tension γ whith time is an oscillating process. The measurement of γ during an oscillation observed for a system evolving slowly, is a linear function of the square root of time. Furthermore in another series of experiments on similar systems, we have shown that the adsorption-desorption process is faster than the- diffusion one. Therefore we assume, contrarily to SANFELD, that the diffusion process is determining.

  • We show that the interfacial tension essentially depends on the density of \(C_{16}^ +\) ions at the interface, whatever be the bounded counter ion. This density will depend only on the C16Pi or C16Cl concentration in the two little zones of the bulk adjacent to the interface. Inside of them a chemical oscillating reaction would take place which would make the concentrations of the two species vary with time. From these hypothesis we are now studying the coupling between the chemical reaction and hydrodynamics in collaboration with hydrodynamicists.

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Bibliographie

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Copyright information

© Springer-Verlag Berlin Heidelberg 1979

Authors and Affiliations

  • M. Dupeyrat
  • E. Nakache

There are no affiliations available

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