Spontaneous Emulsification Produced by Diffusion — A Review
Abstract
Some observations of and possible explanations for spontaneous emulsification are reviewed. Emphasis is on situations where diffusion produces regions of local supersaturation and consequently nucleation of emulsion drops. In surfactant systems swelling of the lamellar liquid crystalline phase in the form of myelinic figures and vesicular structures can also lead to spontaneous formation of dispersions. The importance of knowledge of system phase behavior in understanding the origin of emulsification is stressed, especially in surfactant systems where various micellar solutions, microemulsions, and lyotropic liquid crystals may occur. It is possible that lack of such knowledge may have led to oversimplified explanations of emulsification in some systems in the past.
References (33)
- W.J. Benton et al.
J. Colloid Interface Sci.
(1986) - S.E. Friberg et al.
Sep. Sci. Technol.
(1985) - N. Gains et al.
J. Membr. Sci.
(1985) - S. Kislalioglu et al.
- A. Kotidou et al.
J. Colloid Interface Sci.
(1983) - C.A. Miller et al.
J. Colloid Interface Sci.
(1970) - C.A. Miller et al.
J. Colloid Interface Sci.
(1970) - K.H. Raney et al.
J. Colloid Interface Sci.
(1987) - I. Sakurai et al.
Biochem. Biophys. Acta
(1984) - A. Saupe
J. Colloid Interface Sci.
(1977)
J. Am. Oil. Chem. Soc.
J. Disp. Sci. Tech.
Proc. Int. Congr. Surf. Act. 2nd
Trans. Faraday Soc.
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