Dilatant, Dilatancy

In rheology, a fluid is called dilatant when its apparent viscosity increases with increasing shear rate. Such systems are also referred to as shear-thickening fluids. A commonly used model is the power law (Ostwald-de Waele model):

η = K · γ′ exp (n – 1)

• η: apparent viscosity
• γ′: shear rate
• K: consistency index
• n: flow index, in dilatant systems n > 1.

For n > 1, the shear stress increases disproportionately with the shear rate; the viscosity then increases with the shear rate.

When mixing solids, highly filled suspensions or pasty agglomerates can exhibit dilatant behavior. This leads to increasing drive torques and forces at higher mixing or conveying speeds and must be taken into account when designing drives and tool geometries.

In amixon® equipment, almost all material consistencies can be precisely homogenized. These include dilatant, shear-thinning, well-flowing and poorly flowing powders.