Unusual Phase Behavior in a Two-Component System Catanionic Surfactant-Water: From Lamellar-Lamellar to Vesicle-Micelle Coexistence

• Type: Chapter or Part of a Book
• Date: 2012

Authors

Bruno F B Silva (Author) Other; Eduardo F Marques (Author) FCUP; Ulf Olsson (Author) Other

Book

Title: Recent Trends in Surface and Colloid Science vol. 12

Pages: 69-84

Indexing

ISI Web of Knowledge - 0 Citations

Scientific classification

FOS: Natural sciences > Chemical sciences

Other information

Authenticus ID: P-005-KG9

DOI: 10.1142/9789814299428_0006

Abstract (EN): Salt-free catanionic surfactants form in water binary systems, thus differing from pseudo-ternary equimolar catanionic mixtures, where salt is present. A miscibility gap, an unusual phenomenon in binary systems, is observed for the lamellar phase of the catanionic surfactant hexadecyltrimethylammonium octylsulfonate. Experimental data show the coexistence of a swollen and a collapsed lamellar phase in a wide two-phase region, while linear swelling is observed for each phase. This phase behavior is suggested to stem mainly from a concentration dependence of the charge density of catanionic bilayer, driven by the much higher solubility of the short chain ionic counterpart (octylsulfonate). Thus, a theoretical cell model based on combined DLVO and short range repulsive potentials is presented in order to provide physical insight into the miscibility gap. Furthermore, the surfactant forms at high dilution a solution phase and exhibits a very low critical micelle concentration (0.0035 wt%). The dilute lamellar phase is in equilibrium with the isotropic solution, and small vesicles can also be observed, apparently as a dispersion of the swollen lamellae in the solution. Upon temperature increase, a vesicle-to-micelle transition occurs. These unusual equilibria can also be qualitatively rationalized by the short chain solubility model.

Language: English

Type (Professor's evaluation): Scientific