Aging effects of precipitated silica in poly(dimethylsiloxane)

e report the transformation from gels to viscous fluids within a time period of 101–103 h in ixtures of precipitated silica in silicone oil. Scaling behavior in elastic and viscous moduli versus requency, similar to that reported by Trappe and Weitz Phys. Rev. Lett. 85, 449–452 2000 , has een observed for suspensions of different ages, silica volume fractions, and silicone oil molecular eights; this shows self-similarity in the stress-bearing silica network in these samples. The elastic lateau modulus, extracted from the scaling of the moduli for each suspension, decays xponentially with time, but the initial plateau modulus depends only on the silica volume fraction nd is independent of the properties of the base fluids. The aging time constant is larger if thinner ilicone oil or a higher silica volume fraction is used. The aging rate is slower for silica in ethyl-terminated silicone oil than that in hydroxyl-terminated silicone oil by about an order of agnitude. We attribute the aging effects to the adsorption of poly dimethylsiloxane on silica and se a model based on the “poisons” model by Cohen-Addad and de Gennes C. R. Ocad. Sci. aris, Série II 319, 25–3