title: Effects of alkyl chain length on synergetic adsorption and micelle formation in homologous cationic surfactant mixtures.
abstract: The surface tensions (gamma) of the aqueous solutions of tetradecyltrimethylammonium bromide (TTAB) and dodecyltrimethylammonium bromide (DTAB) were measured as a function of the total molality of surfactants (m) and the relative proportion (composition) of DTAB (X(2)) at 298.15 +/- 0.05 K under atmospheric pressure. The effect of the difference in the hydrophobic chain length between hexadecyltrimethylammonium bromide (HTAB) and DTAB on the synergism was examined. This synergism was observed in the miscibility at the surface of a mixture of these two compounds. The excess Gibbs energy of adsorption of the TTAB-DTAB system was positive in contrast to the HTAB-DTAB system. This indicates that there are certain restrictions on the difference in the hydrophobic chain length for the synergism to be brought about in homologous cationic surfactant mixtures. This mechanism was explained by the theory of a staggered structure formation at the air/water interface. A similar argument successfully applied to the hexadecyltrimethylammonium chloride (HTAC)-dodecyltrimethylammonium chloride (DTAC) and tetradecyltrimethylammonium chloride (TTAC)-DTAC mixtures also.
authors.affiliation: Department of Chemistry, Faculty of Science, Kyushu University, Fukuoka 812-8581, Japan. h.matsubara@mbox.nc.kyushu.ac.jp
authors.forename: Hiroki
authors.initials: H
authors.lastname: Matsubara
authors.forename: Takayuki
authors.initials: T
authors.lastname: Nakano
authors.forename: Takashi
authors.initials: T
authors.lastname: Matsuda
authors.forename: Takanori
authors.initials: T
authors.lastname: Takiue
authors.forename: Makoto
authors.initials: M
authors.lastname: Aratono