Dynamic viscoelastic properties of silica alkoxide during the sol-gel transition
Laboratoire de Biorhéologie et d’Hydrodynamique Physico-chimique UMR 7057 et Fédération de Recherche Matiéres et Systémes Complexes FR 2438, Université Paris 7 Denis Diderot, case 7056, 2 place, Jussieu, 75251, Paris, Cedex 05, France
2 Département Systéme Energétique et Environnement, Ecole des Mines de Nantes, 4 rue Alfred Kastler, BP 20722, 44307, Nantes Cedex 03, France
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The viscoelastic properties of silica alkoxide gel during the sol-gel transition (SGT) are analysed using an extended shear relaxation modulus expression with a functional form based on a product of power law and Debye-Maxwell relaxation kernels. The dynamic properties are probed by small-amplitude oscillatory shear measurements in three viscoelastic domains (pre-SGT, SGT, post-SGT). Using analytical expressions for the storage and loss moduli in these three domains, it is shown that the divergence of the mean characteristic relaxation time in the pre-SGT domain can be successfully described by a percolation with bond fluctuation dynamics. It is also shown that the equilibrium shear modulus in the post-SGT domain can be successfully described by a percolation model based on an analogy with an electrical network. The amplitude and the critical exponent of the power law relaxation at the gelation time first introduced by Winter and Chambon are estimated in the pre- and post-SGT domains.
© EDP Sciences, Società Italiana di Fisica, and Springer-Verlag, 2003