title: Study on Colloid Vibration Current in Aqueous Solution of Binary Surfactant Mixtures: Effects of Counterions and Hydrophobic Chains.
abstract: In order to elucidate an electroacoustic phenomenon of mixed micelles in an aqueous solution, we measured the colloid vibration current (CVI) in aqueous solutions of binary surfactant mixtures. Based on the thermodynamic treatment of critical micelle concentration (cmc) values determined by conductivity measurements, it was expected that dodecyltrimethylammonium bromide (DTAB) and dodecyltrimethylammonium chloride (DTAC) molecules would mix ideally in the micelle. However, the micelle composition as evaluated from the CVI measurement, based on the linear dependence of the CVI value on the micelle composition, differed from the aforementioned ideality. Considering these observations, we concluded that the CVI measurement was more sensitive to the counterion distribution near the micelle surface, whereas the thermodynamically determined micelle composition included the counterions more loosely bound in the diffuse double layer due to the electroneutrality condition included in its assumption. On the other hand, the phase diagram illustrating micelle formation in the lithium dodecyl sulfate (LiDS) - lithium perfluorooctane sulfonate (LiFOS) mixture system showed a heteroazeotropic point arising from the stronger interactions between homologous surfactants than between heterologous ones. Although the concentration dependence of CVI values was expected to drastically change at a heteroazeotropic point due to the enormous variation in the density of the micelle core, the results showed a monotonous change, which suggests that the density of the micelle core varies continuously. By taking the partial molar volume of fluorocarbon compounds in the hydrocarbon compounds into account, the density of the micelle core was affected by the size of the micelle as well as its constituents.
authors.affiliation: Department of Chemical and Biological Engineering, National Institute of Technology, Ube College.
authors.forename: Youichi
authors.initials: Y
authors.lastname: Takata
authors.forename: Atsushi
authors.initials: A
authors.lastname: Hyono
authors.forename: Hiroyuki
authors.initials: H
authors.lastname: Ohshima
mesh_terms: D017738:Alkanesulfonic Acids / Q000737:chemistry; D000838:Anions; D003102:Colloids; D004553:Electric Conductivity; D005466:Fluorocarbons / Q000737:chemistry; D057927:Hydrophobic and Hydrophilic Interactions; D008823:Micelles; D015394:Molecular Structure; D000644:Quaternary Ammonium Compounds / Q000737:chemistry*; D012967:Sodium Dodecyl Sulfate / Q000737:chemistry; D013501:Surface-Active Agents / Q000737:chemistry*; D013816:Thermodynamics; D000069453:Ultrasonic Waves; D014867:Water / Q000737:chemistry
chemical_list: D017738:Alkanesulfonic Acids; D000838:Anions; D003102:Colloids; D005466:Fluorocarbons; D008823:Micelles; D000644:Quaternary Ammonium Compounds; D013501:Surface-Active Agents; D014867:Water; D012967:Sodium Dodecyl Sulfate; C076994:perfluorooctane sulfonic acid; C028913:dodecyl sulfate; C022806:dodecyltrimethylammonium