Issue
EPL
Volume 77, Number 1, January 2007
Article Number 18007
Number of page(s) 5
Section Interdisciplinary Physics and Related Areas of Science and Technology
DOI http://dx.doi.org/10.1209/0295-5075/77/18007
Published online 10 January 2007
EPL, 77 (2007) 18007
DOI: 10.1209/0295-5075/77/18007

Superdiffusion of concentration in wormlike-micelle solutions

R. Ganapathy, A. K. Sood and S. Ramaswamy

Department of Physics, Indian Institute of Science - Bangalore, 560012, India


received 19 June 2006; accepted in final form 9 November 2006; published January 2007
published online 10 January 2007

Abstract
Our dynamic light scattering studies of viscoelastic wormlike-micelle solutions of surfactant cetyltrimethylammonium tosylate (CTAT) show superdiffusive relaxation of concentration fluctuations: relaxation rate $\sim q^{z}$ at wavenumber q, with z < 2, at concentrations just past overlap. Linear rheology experiments show that the micellar recombination kinetics in this system is diffusion-controlled (micelles break and recombine with their original partners). Addition of 10 mM to 100 mM of sodium chloride (NaCl), takes the system from the diffusion-controlled (DC) regime to mean-field recombination kinetics regime where micellar ends combine with ends belonging to other micelles. In the mean-field regime, the concentration fluctuations decay in a purely diffusive manner. We suggest a qualitative explanation for the observed superdiffusive behaviour in the DC regime.

PACS
82.70.Uv - Surfactants, micellar solutions, vesicles, lamellae, amphiphillic systems (hydrophilic and hydrophobic interaction).
05.40.Fb - Random walks and Levy flights.
82.70.Gg - Gels and sols.

© Europhysics Letters Association 2007