Eur. Phys. J. E 11, 7-20 (2003)
DOI: 10.1140/epje/i2002-10124-y

Synergistic effects in mixed wormlike micelles of dimeric and single-chain cationic surfactants at high ionic strength

C. Oelschlaeger¹, E. Buhler², G. Waton¹ and S.J. Candau<sup>1

1</sup>  Laboratoire de Dynamique des Fluides Complexes, U.M.R. n° 7506, Université Louis Pasteur, C.N.R.S., 4 rue Blaise Pascal, 67070 Strasbourg Cedex, France
²  Groupe de Dynamique des Phases Condensées, U.M.R. n° 5581, Université Montpellier 2, cc 26, 34095 Montpellier, Cedex 5, France

candau@fresnel.u-strasbg.fr

(Received 18 November 2002 and Received in final form 18 March 2003 / Published online: 27 May 2003)

Abstract
The mixed micellization between the cationic gemini surfactant [ ( ) ₂N ⁺( ) N ⁺ ( ) ₂ ] and the cationic cetyltrimethylammonium bromide (CTAB) in 150 mM KBr solutions has been investigated. The variation of the cmc of the mixtures, measured by surface tension experiments, with composition revealed synergism in micelle formation. T-Jump and light scattering experiments performed in the vicinity of the crossover volume fraction showed the existence of two micellar populations, possibly linear and toroidal micelles. Rheological and dynamic light scattering experiments allowed to fully characterize the linear viscoelasticity of the mixtures. These measurements revealed synergistic gains in viscoelastic properties with a maximum of the stress-relaxation time around the equimolar composition. These effects are ascribed to a progressive intermicellar crosslinking resulting from a continuous increase of the end-cap energy with the 12-2-12 content in the mixture.

PACS
82.70.Uv - Surfactants, micellar solutions, vesicles, lamellae, amphiphilic systems, (hydrophilic and hydrophobic interactions).
61.25.Hq - Macromolecular and polymer solutions; polymer melts; swelling.
83.60.Bc - Linear viscoelasticity.

© EDP Sciences, Società Italiana di Fisica, Springer-Verlag 2003