title: Effect of the nature of the spacer on the aggregation properties of gemini surfactants in an aqueous solution.
abstract: The aggregation properties of three dicationic quaternary ammonium gemini surfactants with the same structure, except the spacer group, diethyl ether, six methylene, and p-xylyl, have been studied using electrical conductivity and fluorescence. The critical micelle concentration (cmc) and the micelle aggregation number (N) were determined, and the micropolarity and the microviscosity of the micelle were characterized. The micelle ionization degree (alpha) was obtained by a combination of the electrical conductivity data and the micelle aggregation number. Furthermore, the Gibbs free energy of micellization (deltaGmic) was studied. These results have shown that the nature of the spacer has an important effect on the aggregation properties of gemini surfactants in an aqueous solution. A hydrophilic, flexible spacer prompts micelle formation, which leads to a smaller cmc, smaller alpha, larger N, and more negative deltaGmic. Meanwhile, the microviscosity study indicates that the gemini surfactant with a hydrophilic, flexible spacer forms a more closely packed micelle structure than the one with a hydrophobic, rigid spacer.
authors.affiliation: Key Laboratory of Colloid and Interface Science, Center for Molecular Science, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100080, People's Republic of China.
authors.forename: Xiaoyong
authors.initials: X
authors.lastname: Wang
authors.forename: Jinben
authors.initials: J
authors.lastname: Wang
authors.forename: Yilin
authors.initials: Y
authors.lastname: Wang
authors.forename: Haike
authors.initials: H
authors.lastname: Yan
authors.forename: Peixun
authors.initials: P
authors.lastname: Li
authors.forename: Robert K
authors.initials: RK
authors.lastname: Thomas
mesh_terms: D004553:Electric Conductivity; D005454:Fluorescence Polarization / Q000379:methods; D008823:Micelles; D000644:Quaternary Ammonium Compounds / Q000737:chemistry*; D012996:Solutions / Q000737:chemistry; D013499:Surface Properties; D013501:Surface-Active Agents / Q000737:chemistry*; D013816:Thermodynamics; D014783:Viscosity; D014867:Water / Q000737:chemistry
chemical_list: D008823:Micelles; D000644:Quaternary Ammonium Compounds; D012996:Solutions; D013501:Surface-Active Agents; D014867:Water