title: Hexadecyltrimethylammonium bromide (CTA-Br) and 1-butyl-3-methylimidazolium tetrafluoroborate (bmim-BF4) in aqueous solution: An ephemeral binary system.
abstract: OBJECTIVE
  Mixtures of the cationic surfactant hexadecyltrimethylammonium bromide (CTA-Br) and the ionic liquid 1-butyl-3-methylimidazolium tetrafluoroborate (bmim-BF4) in aqueous solutions are expected to behave as typical binary cationic surfactant system taking into account the surface activity displayed by the ionic liquid, instead of considering the IL as a water cosolvent.
  
  
  METHODS
  Surface tension and conductivity measurements have been conducted as a function of the total concentration of the mixtures at different surfactant mole fraction (αCTA-Br) to investigate the surface active properties.
  
  
  RESULTS
  Turbidity immediately appearing when the compounds are mixed in water suggests the spontaneous formation of the low soluble compound hexadecyltrimethylammonium tetrafluoroborate (CTA-BF4), together with the salt formed by the respective counterions bmim+and Br-in solution. For αCTA-Br≠0.5, furthermore of the mentioned compounds, the spare bmim-BF4(for αCTA-Br<0.5) or CTA-Br (for αCTA-Br>0.5), are also present in the aqueous solution. Systems containing excess of bmim-BF4show a low critical aggregate concentration (cac), but an unexpected high surface tension at cac (γcac≈53-56mN/m), as pure CTA-BF4. For systems containing excess of CTA-Br, cac increases but γcacdecreases up to 36mN/m. Mixtures of pure CTA-BF4and bmim-BF4or CTA-Br behave as typical binary surfactant systems.
authors.affiliation: Department of Chemical and Surfactants Technology, Institute of Advanced Chemistry of Catalonia (IQAC-CSIC), Barcelona, Spain. Electronic address: fcffte@cid.csic.es.
authors.forename: Francesc
authors.initials: F
authors.lastname: Comelles
authors.affiliation: Department of Chemical and Surfactants Technology, Institute of Advanced Chemistry of Catalonia (IQAC-CSIC), Barcelona, Spain. Electronic address: irfbet@cid.csic.es.
authors.forename: Isabel
authors.initials: I
authors.lastname: Ribosa
authors.affiliation: Department of Chemical and Surfactants Technology, Institute of Advanced Chemistry of Catalonia (IQAC-CSIC), Barcelona, Spain. Electronic address: juanj.g@gmail.com.
authors.forename: Juan José
authors.initials: JJ
authors.lastname: Gonzalez
authors.affiliation: Department of Chemical and Surfactants Technology, Institute of Advanced Chemistry of Catalonia (IQAC-CSIC), Barcelona, Spain. Electronic address: teresa.garcia@iqac.csic.es.
authors.forename: M Teresa
authors.initials: MT
authors.lastname: Garcia
keywords: Binary systems; CTA-BF(4); CTAB; Cationic surfactant; Conductivity; Ionic liquid; Surface tension; Synergism; bmim-BF(4); cac