title: Phase transition in salt-free catanionic surfactant mixtures induced by temperature.
abstract: Aggregate transitions in salt-free catanionic surfactant mixtures of tetradecyltrimethylammonium hydroxide (TTAOH)/fatty acid were investigated as a function of surfactant concentration and temperature. Lauric acid (LA), myristic acid (MA), and palmitic acid (PA) were chosen for the current study. The TTAOH/LA mixture exhibited rich phase behavior at room temperature. With increasing total surfactant concentration (c(T)), a bluish vesicular (L(alphav)) phase, an isotropic micellar (L(1)) phase, and a birefringent lamellar (L(alpha)) phase were observed. Between the L(alphav) phase and the L(1) phase, a narrow L(alpha)'/L(1) two-phase region was determined. With increasing temperature, a transition from the L(alpha) phase to the L(1) phase was induced at higher c(T) whereas at lower c(T) an opposite transition from the L(1) phase to the L(alphav) phase was noticed. Thus surprisingly, we observed bilayer-to-micelle and micelle-to-bilayer transitions in the same catanionic surfactant system, both induced by the temperature increase. Replacing LA by MA and PA caused a continuous increase in the average Krafft point of the mixture. The L(alphav)-phase region and phase-separated region become larger. Moreover, a single L(1)-phase region was absent within the investigated temperature range.
authors.affiliation: Department III, Institute of Physical Chemistry, Polish Academy of Sciences, Kasprzaka 44/52, 01-224 Warsaw, Poland.
authors.forename: Hongguang
authors.initials: H
authors.lastname: Li
authors.forename: Stefan A
authors.initials: SA
authors.lastname: Wieczorek
authors.forename: Xia
authors.initials: X
authors.lastname: Xin
authors.forename: Tomasz
authors.initials: T
authors.lastname: Kalwarczyk
authors.forename: Natalia
authors.initials: N
authors.lastname: Ziebacz
authors.forename: Tomasz
authors.initials: T
authors.lastname: Szymborski
authors.forename: Robert
authors.initials: R
authors.lastname: Hołyst
authors.forename: Jingcheng
authors.initials: J
authors.lastname: Hao
authors.forename: Ewa
authors.initials: E
authors.lastname: Gorecka
authors.forename: Damian
authors.initials: D
authors.lastname: Pociecha