title: Microemulsions of Record Low Amphiphile Concentrations Are Affected by the Ambient Gravitational Field.
abstract: It is shown that the ternary system heavy water-heptane-hexadecyl hexaethylene oxide (C16E6) has a stable bicontinuous microemulsion phase down to an exceptionally low concentration at the balanced temperature of 26.8 °C. It is further demonstrated that the ambient gravitational field has an influence on the observed phase equilibria for typical sample sizes (∼1 cm). Direct measurements using a nuclear magnetic resonance imaging technique demonstrate that sample compositions vary with the height in the vials. It is furthermore found that some samples show four phases at equilibrium in apparent violation of Gibbs' phase rule. It is pointed out that Gibbs' phase rule strictly applies only when effects of gravity are negligible. A further consequence of the ambient gravitational field is that, for the system studied, the microemulsion one-phase samples are not observed, when using standard size vials, that is, sample heights on the order of a centimeter. Quantitative determinations of concentration profiles can be used to determine parameters of the free-energy density for the system.
authors.affiliation: Physical Chemistry, Lund University , Box 124, SE-221 00 Lund, Sweden.|Kao Cooperation , 2-1-3 Bunka, Sumida-ku, Tokyo 131-8501, Japan.
authors.forename: Kazuhiro
authors.initials: K
authors.lastname: Ishikawa
authors.affiliation: Physical Chemistry, Lund University , Box 124, SE-221 00 Lund, Sweden.
authors.forename: Manja
authors.initials: M
authors.lastname: Behrens
authors.affiliation: Physical Chemistry, Lund University , Box 124, SE-221 00 Lund, Sweden.
authors.forename: Stefanie
authors.initials: S
authors.lastname: Eriksson
authors.affiliation: Physical Chemistry, Lund University , Box 124, SE-221 00 Lund, Sweden.
authors.forename: Daniel
authors.initials: D
authors.lastname: Topgaard
authors.affiliation: Physical Chemistry, Lund University , Box 124, SE-221 00 Lund, Sweden.
authors.forename: Ulf
authors.initials: U
authors.lastname: Olsson
authors.affiliation: Physical Chemistry, Lund University , Box 124, SE-221 00 Lund, Sweden.
authors.forename: Håkan
authors.initials: H
authors.lastname: Wennerström