title: Origin of the sphere-to-rod transition in cationic micelles with aromatic counterions: specific ion hydration in the interfacial region matters.
abstract: Sphere-to-rod transitions of cetyltrimethylammonium (CTA+) micelles with dichlorobenzoate counterions are remarkably substituent dependent. Simultaneous estimates of the interfacial molarities of H2O, MeOH, and Cl- and 2,6- and 3,5-dichlorobenzoate (2,6OBz and 3,5OBz) counterions were obtained by the chemical trapping method in mixed micelles of CTACl/CTA3,5OBz and CTACl/CTA2,6OBz without added salt. Increasing the CTA3,5OBz mole fraction produces a marked concurrent increase in interfacial 3,5OBz- and a decrease in interfacial H2O concentrations through the sphere-to-rod transition. No abrupt concentration changes are observed with increasing CTA2,6OBz mole fraction. Counterion-specific changes in the interfacial water concentration may be a major contributor to the delicate balance of forces governing micellar morphology.
authors.affiliation: Department of Chemical and Biomolecular Engineering, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA.
authors.forename: Yan
authors.initials: Y
authors.lastname: Geng
authors.forename: Laurence S
authors.initials: LS
authors.lastname: Romsted
authors.forename: Sandro
authors.initials: S
authors.lastname: Froehner
authors.forename: Dino
authors.initials: D
authors.lastname: Zanette
authors.forename: Linda J
authors.initials: LJ
authors.lastname: Magid
authors.forename: Iolanda M
authors.initials: IM
authors.lastname: Cuccovia
authors.forename: Hernan
authors.initials: H
authors.lastname: Chaimovich