2018 Impact factor 1.686
Soft Matter and Biological Physics
Eur. Phys. J. E 9, 287-291 (2002)
DOI: 10.1140/epje/i2002-10075-3

Anomalous dynamical light scattering in soft glassy gels

J.-P. Bouchaud1 and E. Pitard2

1  Service de Physique de l'État Condensé, Centre d'études de Saclay, Orme des Merisiers, 91191 Gif-sur-Yvette Cedex, France
2  Laboratoire de Physique Mathématique et Théorique, Université Montpellier II, UMR 5825, France

bouchau@spec.saclay.cea.fr

(Received 15 April 2002 / Published online: 23 December 2002)

Abstract
We compute the dynamical structure factor $S(q,\tau)$ of an elastic medium where force dipoles appear at random in space and in time, due to "micro-collapses" of the structure. Various regimes are found, depending on the wave vector q and the collapse time $\theta$. In an early time regime, the logarithm of the structure factor behaves as $(q\tau)^{3/2}$, as predicted in (L. Cipelletti et al., Phys. Rev Lett. 84, 2275 (2000)) using heuristic arguments. However, in an intermediate-time regime we rather obtain a $(q
\tau)^{5/4}$ behaviour. Finally, the asymptotic long-time regime is found to behave as $q^{3/2} \tau$. We also give a plausible scenario for aging, in terms of a strain-dependent energy barrier for micro-collapses. The relaxation time is found to grow with the age tw, quasi-exponentially at first, and then as tw4/5 with logarithmic corrections.

PACS
82.70.Gg - Gels and sols.
81.40.Cd - Solid solution hardening, precipitation hardening, and dispersion hardening; aging.

© EDP Sciences, Società Italiana di Fisica, Springer-Verlag 2002