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Rheological behavior of nanosized silica suspensions

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Most materials behave in such a way that they have a combination of viscous and elastic response under stress or deformation. Materials behave in linear manner, as described by Hooke or Newton, on in a small scale. Among real liquids the Newtonian and non-Newtonian fluids can be distinguished. Viscosity is one of the rheological parameters which can characterize the liquids. By measurements of the viscosity versus share rate one can classify the liquid into a particular group. If the viscosity is decreasing vs. shear rate the liquid has shear thinning properties, when the viscosity is rapidly increasing the shear thickening effect or dilatancy is observed. The rheological classification of liquids is presented in Figure 1 [1]. Shear thickening effect appears in suspensions having various concentration and morphology of solid phase. The shear thickening of fluids can be explained by a few theories. The most popular is the clustering theory. According to its main assumption the particles, at low shear rates, are prevented from aggregation by steric repulsive and Brownian forces. Under increasing shear rate the hydrodynamic forces also increase and the particles form chains, blocking the flow of the fluid. The next potential explanation of the dilatancy phenomenon, is Order-Disorder Transition (ODT) theory, which claims that t[...]

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