Tricritical points in H2O-oil-amphiphile mixtures

M. Kahlweit, R. Strey, Makoto Aratono, G. Busse, J. Jen, K. V. Schubert

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Abstract

Quaternary mixtures of water (A), an oil (B), a nonionic amphiphile (C), and an appropriately chosen fourth component offer an opportunity for searching for tricritical points (tcp) at atmospheric pressure. It is shown thatfor reaching a tcp, one has to couple an A-B-C mixture that shows the phase sequence 2→3→2 with rising temperature, with a second ternary mixture that shows a 2→2 transition, the bar denoting in which of the two phases the amphiphile is mainly dissolved. With weakly structured solutions, that is, with short-chain amphiphiles as (C) this can be done by either adding an oil with a lower carbon number, or by adding a nonaqueous polar protic solvent such as formamide. With strongly structured solutions, that is, with long-chain amphiphiles, one has to add a short-chain amphiphile for destroying the structure as a prerequisite for reaching a tcp. Insofar, our earlier presumption that with long-chain amphiphiles, a tcp may also be reached, either by increasing their amphiphilicity or by lowering the carbon number of the oil, does not seem to apply. Experience shows that in A-B-C′ mixtures with sufficiently short-chain amphiphiles as C′ that separate into three phases: the amphiphile-rich middle phase always wets the A/B interface. If a short-chain amphiphile is added to an A-B-C mixture with a nonwetting middle phase one will, therefore, inevitably find a nonwetting→wetting transition as one approaches a tcp.

Original languageEnglish
Pages (from-to)2842-2853
Number of pages12
JournalThe Journal of Chemical Physics
Volume95
Issue number4
DOIs
Publication statusPublished - 1991
Externally publishedYes

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All Science Journal Classification (ASJC) codes

  • Physics and Astronomy(all)
  • Physical and Theoretical Chemistry

Cite this

Kahlweit, M., Strey, R., Aratono, M., Busse, G., Jen, J., & Schubert, K. V. (1991). Tricritical points in H2O-oil-amphiphile mixtures. The Journal of Chemical Physics, 95(4), 2842-2853. https://doi.org/10.1063/1.460937