Non-linear viscoelastic behavior of fumed silica suspensions

Suspensions of fumed silica exhibit a wide range of rheological properties depending on the nature and magnitude of the interparticle forces. In a non -polar fluid, the particles interact through hydrogen bonding and can form a three-dimensional network. The microstructure formation is responsible fo r the non-linear viscoelastic behavior of fumed silica suspensions, even at very small strain. These non-linear rheological properties have been studi ed in small amplitude oscillatory experiments as a function of particle siz e, surface treatment of particles, suspending medium polarity and solids co ncentration. The non-linear viscoelastic behavior is characterized by a non -sinusoidal waveform of the signal response. For suspensions in a non-polar fluid, both the elastic and the loss moduli are shown to be sensitive to t he strain amplitude: the elastic modulus is decreasing with increasing stra in whereas the loss moduli is initially increasing with strain. We have cho sen to examine the dissipated energy which is clearly related to the breaku p of the suspension structure. A comparison of model predictions and the ex perimental data shows the limitations of these models, recently proposed in the literature to describe the behavior of colloidal suspensions.