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

• Tipo: Capítulo ou Parte de Livro
• Data: 2012

Autores

Bruno F B Silva (Autor) Outra; Eduardo F Marques (Autor) FCUP; Ulf Olsson (Autor) Outra

Livro

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

Páginas: 69-84

Indexação

ISI Web of Knowledge - 0 Citações

Classificação Científica

FOS: Ciências exactas e naturais > Química

Outras Informações

ID Authenticus: 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.

Idioma: Inglês

Tipo (Avaliação Docente): Científica