Stability, Phase Equilibria, and Interfacial Free Energy in Microemulsions

  • E. Ruckenstein

Abstract

The stability of emulsions is examined from the points of view of thermodynamics as well as dynamics. First a statistical thermodynamical treatment is developed, which demonstrates that, in contrast to usual emulsions, microemulsions can be stable from a thermodynamic point of view. The expression established for the free energy of formation of microemulsions predicts phase inversion from one type of microemulsion to the other one as well as phase separation. Several basic types of multiphase systems are found theoretically:
  1. (1)

    microemulsion in equilibrium with another (in particular dilute) microemulsion of oil-in-water;

     
  2. (2)

    microemulsion in equilibrium with another (in particular dilute) microemulsion of water-in-oil, and

     
  3. (3)

    a dilute microemulsion of water-in-oil in equilibrium with a dilute microemulsion of oil-in-water. Similar multiphase systems have been previously identified experimentally by Winsor and by Healy et al. The present expressions also explain the low values of the interfacial free energy between two microemulsion phases in equilibrium. Second, a transport equation is established for a concentrated colloidal system. Based on this equation conditions are identified when the system is stable or unstable to small perturbations and information about its time evolution obtained. This dynamic approach provides a time scale for significant changes to occur in an unstable system.

     

Keywords

Entropy Surfactant Convection Assure Flocculation 

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Copyright information

© Plenum Press, New York 1977

Authors and Affiliations

  • E. Ruckenstein
    • 1
  1. 1.Faculty of Engineering and Applied SciencesState University of New York at BuffaloBuffaloUSA

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