title: Binary and ternary phase behaviors of short double-chain quaternary ammonium amphiphiles: surface tension, polarized optical microscopy, and SAXS investigations.
abstract: A series of short chain dialkyldimethylammonium amphiphiles ([DiC(n)][X] and [DiC(n)]2[X] with n = 6, 8, or 10) has been investigated as a function of the nature of the counteranion [X] (Cl(-) and Br(-) as classical references and MoO4(2-) and WO4(2-) as catalytic anions). Critical aggregation concentrations (CACs) in water were determined by surface tension measurements, and the binary phase diagrams of the surfactant/water systems were established using polarized optical microscopy (POM) and small angle X-ray scattering (SAXS). The evolution of microstructures and lyotropic phases were discussed in terms of surfactant chain length and counterion effect. A cubic phase region was observed for the divalent counteranions associated with the intermediate chain length, i.e., [DiC8]2[MoO4] and [DiC8]2[WO4]. Finally, the fish diagrams reflecting the polyphasic microemulsion phase behavior of the water/amphiphile/oil ternary systems were established using the carbon number of mono- and dichlorinated n-alkanes as a scan variable. The amphiphile efficiency was also discussed according to the chain length and the nature of the counterions. The hydrophilic-lipophilic behavior of the amphiphiles was evaluated on the basis of the fish diagrams allowing their classification according to the Hofmeister anion sequence. The unusual behavior of [DiC8][Cl] and [DiC8]2[MO4] (M = W or Mo) is highlighted by all experiments: these compounds are clearly intermediates between hydrotropes, [DiC6] cation, and surfactants, [DiC10] cation.
authors.affiliation: Université Lille 1 and ENSCL , EA 4478 Chimie Moléculaire et Formulation, F-59655 Villeneuve d'Ascq Cedex, France.
authors.forename: Bing
authors.initials: B
authors.lastname: Hong
authors.forename: Jonathan
authors.initials: J
authors.lastname: Lai
authors.forename: Loïc
authors.initials: L
authors.lastname: Leclercq
authors.forename: Marion
authors.initials: M
authors.lastname: Collinet-Fressancourt
authors.forename: Jean-Marie
authors.initials: JM
authors.lastname: Aubry
authors.forename: Pierre
authors.initials: P
authors.lastname: Bauduin
authors.forename: Véronique
authors.initials: V
authors.lastname: Nardello-Rataj