NemNewtoniás

nemNewtoniás is a term used to describe materials whose flow behavior does not follow Newton's law of viscosity. In contrast to Newtonian fluids, which have a constant viscosity independent of shear rate, nemNewtoniás exhibit a viscosity that changes with shear rate, time, or both. This makes their flow response more complex and often dependent on the history of applied stress.

The core distinction lies in the relationship between shear stress and shear rate. For Newtonian fluids, shear stress is proportional to shear rate with a single constant viscosity. NemNewtoniás may display non-linear stress–shear rate relationships, time-dependent changes, or the presence of a yield stress that must be exceeded before flow begins. These behaviors can be observed under different conditions and are commonly categorized by time independence or time dependence.

Time-independent nemNewtoniás include shear-thinning (pseudoplastic) fluids, where viscosity decreases with increasing shear rate; shear-thickening (dilatant) fluids, where viscosity increases with shear rate; and yield-stress fluids (Bingham plastics) that require a finite stress to initiate flow. Time-dependent nemNewtoniás exhibit viscosity changes over time under constant shear, such as thixotropic fluids that become less viscous with time, and rheopectic fluids that become more viscous. Many nemNewtoniás also show viscoelastic behavior, combining viscous flow with elastic response.

Common examples range from ketchup and paint to toothpaste, shampoos, and cornstarch–water mixtures (oobleck). NemNewtoniás are widely studied in rheology and have diverse applications in food, cosmetics, materials science, and petroleum engineering. Measuring their properties typically involves rheometers that assess viscosity as a function of shear rate and time.