title: Coacervation and aggregate transitions of a cationic ammonium gemini surfactant with sodium benzoate in aqueous solution.
abstract: Coacervation in an aqueous solution of cationic ammonium gemini surfactant hexamethylene-1,6-bis(dodecyldimethylammonium bromide) (C12C6C12Br2) with sodium benzoate (NaBz) has been investigated at 25 °C by turbidity titration, light microscopy, dynamic light scattering, cryogenic temperature transmission electron microscopy (Cryo-TEM), scanning electron microscopy (SEM), isothermal titration calorimetry, ζ potential and (1)H NMR measurements. There is a critical NaBz concentration of 0.10 M, only above which coacervation can take place. However, if the NaBz concentration is too large, coacervation also becomes difficult. Coacervation takes place at a very low concentration of C12C6C12Br2 and exists in a very wide concentration region of C12C6C12Br2. The phase behavior in the NaBz concentration from 0.15 to 0.50 M includes spherical micelles, threadlike micelles, coacervation, and precipitation. With increasing NaBz concentration, the phase boundaries of coacervation shift to higher C12C6C12Br2 concentration. Moreover, the C12C6C12Br2-NaBz aggregates in the coacervate are found to be close to charge neutralized. The Cryo-TEM and SEM images of the coacervate shows a layer-layer stacking structure consisting of a three-dimensional network formed by the assembly of threadlike micelles. Long, dense and almost uncharged threadlike micelles are the precursors of coacervation in the system.
authors.affiliation: Key Laboratory of Colloid and Interface Science, Beijing National Laboratory for Molecular Sciences (BNLMS), Institute of Chemistry, Chinese Academy of Sciences, Beijing, China. yilinwang@iccas.ac.cn.
authors.forename: Ruijuan
authors.initials: R
authors.lastname: Wang
authors.forename: Maozhang
authors.initials: M
authors.lastname: Tian
authors.forename: Yilin
authors.initials: Y
authors.lastname: Wang
mesh_terms: D064751:Ammonium Compounds / Q000737:chemistry*; D001965:Bromides / Q000737:chemistry; D002151:Calorimetry; D008823:Micelles; D046529:Microscopy, Electron, Transmission; D020160:Sodium Benzoate / Q000737:chemistry; D014867:Water / Q000737:chemistry*
chemical_list: D064751:Ammonium Compounds; D001965:Bromides; D008823:Micelles; D014867:Water; D020160:Sodium Benzoate