Dynamics of concentrated colloidal suspensions during drying --aging, rejuvenation and overaging
Laboratoire de Physico-chimie Macromoléculaire, CNRS UMR7615, ESPCI, 10 rue Vauquelin, 75231, Paris cedex 05, France
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We report on the slow dynamics of concentrated colloidal suspensions during drying and rewetting under conditions of reversible concentration changes without coalescence or aggregation. We used multispeckle diffusing-wave spectroscopy to monitor the slow dynamics of particles. We found that the relaxation of the suspensions exhibits successively slowing-down, acceleration and a stationary regime during drying at constant rates. Under rewetting conditions, we observed slowing-down and a stationary regime. The characteristic time of the stationary regime is inversely proportional to the rate of concentration change and identical for both drying and rewetting. We explain these regimes as aging (overaging), rejuvenation and plastic flow of the suspensions induced by a deviatoric stress (a combination of compressive and elongational stresses) which is induced by the uniaxial compressive strain generated by evaporation.
© EDP Sciences, Società Italiana di Fisica, and Springer-Verlag, 2004