Anomalous dynamical light scattering in soft glassy gels |
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Authors: | J-P Bouchaud E Pitard |
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Institution: | (1) Service de Physique de l'état Condensé, Centre d'études de Saclay, Orme des Merisiers, 91191 Gif-sur-Yvette Cedex, France, FR;(2) Laboratoire de Physique Mathématique et Théorique, Université Montpellier II, UMR 5825, France, FR |
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Abstract: | We compute the dynamical structure factor S(q,τ) 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 θ. In an early time regime, the logarithm of the structure factor behaves as (qτ)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 (qτ)5/4 behaviour. Finally, the asymptotic long-time regime is found to behave as q
3/2τ. 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 t
w
4/5 with logarithmic corrections.
Received 15 April 2002 |
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Keywords: | PACS 82 70 Gg Gels and sols – 81 40 Cd Solid solution hardening precipitation hardening and dispersion hardening aging |
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