title: Self-assembly of surfactant vesicles that transform into viscoelastic wormlike micelles upon heating.
abstract: Unilamellar vesicles are observed to form in aqueous solutions of the cationic surfactant, cetyl trimethylammonium bromide (CTAB), when 5-methyl salicylic acid (5mS) is added at slightly larger than equimolar concentrations. When these vesicles are heated above a critical temperature, they transform into long, flexible wormlike micelles. In this process, the solutions switch from low-viscosity, Newtonian fluids to viscoelastic, shear-thinning fluids having much larger zero-shear viscosities (e.g., 1000-fold higher). The onset temperature for this transition increases with the concentration of 5mS at a fixed CTAB content. Small-angle neutron scattering (SANS) measurements show that the phase transition from vesicles to micelles is a continuous one, with the vesicles and micelles coexisting over a narrow range of temperatures. The tunable vesicle-to-micelle transition and the concomitant viscosity increase upon heating may have utility in a range of areas, including microfluidics, controlled release, and tertiary oil recovery.
authors.affiliation: Department of Chemical & Biomolecular Engineering, University of Maryland, College Park, Maryland 20742-2111, USA.
authors.forename: Tanner S
authors.initials: TS
authors.lastname: Davies
authors.forename: Aimee M
authors.initials: AM
authors.lastname: Ketner
authors.forename: Srinivasa R
authors.initials: SR
authors.lastname: Raghavan
mesh_terms: D000077286:Cetrimonium; D002593:Cetrimonium Compounds / Q000737:chemistry*; D006358:Hot Temperature; D008823:Micelles; D033363:Neutron Diffraction; D044367:Phase Transition; D012212:Rheology; D012459:Salicylates / Q000737:chemistry*; D053838:Scattering, Small Angle; D053835:Unilamellar Liposomes / Q000737:chemistry*; D014783:Viscosity
chemical_list: D002593:Cetrimonium Compounds; D008823:Micelles; D012459:Salicylates; D053835:Unilamellar Liposomes; C520964:5-methylsalicylic acid; D000077286:Cetrimonium