shearthickening

Shear thickening, also known as shear-thickening behavior, is a non-Newtonian rheological phenomenon in which the viscosity of a suspension increases with the rate of shear. It is most commonly observed in concentrated suspensions of rigid particles in a liquid, such as corn starch in water, and can cause the material to behave more like a solid at high strain rates.

There are two main regimes: continuous shear thickening (CST) where viscosity rises gradually with shear rate, and discontinuous shear thickening (DST) where the viscosity increases abruptly over a small range of shear rates. In practice, suspensions may show a mix or transition between the regimes depending on conditions.

Two leading explanations are hydroclustering and frictional contact networks. Under increased shear, particles may form transient clusters that hinder flow, or frictional contacts and force chains develop in the crowded suspension, effectively jamming portions of the material. Dilatancy, the tendency of densely packed particles to expand in volume when sheared, can force liquid out of lubrication layers and promote solid-like behavior. The exact mechanism can depend on particle size, shape, roughness, surface chemistry, and particle concentration.

Onset and magnitude depend on particle volume fraction, size distribution, particle shape, and interparticle interactions (steric, electrostatic, van der Waals). Higher concentrations and rougher particles generally promote thicker thickening and earlier onset.

Applications include protective gear, damping systems, and impact-resistant materials that stiffen upon sudden loading. In processing, shear thickening can complicate mixing and pumping, but with proper formulation it can be exploited for tunable rheology. Rheological tests measure viscosity as a function of shear rate or stress; DST appears as a steep jump, CST as a smooth, upward curve.