epäNewtonian

EpäNewtonian is a Finnish adjective used in scientific contexts to denote materials or fluids that do not follow Newton’s law of viscosity. In English the equivalent term is "non-Newtonian." The label is most commonly applied in rheology to describe fluids whose viscosity changes with applied shear rate or shear history, or that exhibit both viscous and elastic behavior.

Characteristics of epäNewtonian fluids include shear thinning (pseudoplasticity), shear thickening (dilatancy), viscoelasticity, thixotropy (time-dependent decrease in viscosity under shear), and rheopexy (time-dependent increase). Common examples are ketchup and paint (shear-thinning), cornstarch suspensions like oobleck (shear-thickening), blood and polymers (viscoelastic), and certain gels and clays (thixotropic).

EpäNewtonian behavior is modeled with constitutive equations such as power-law, Bingham plastic, Herschel–Bulkley, and viscoelastic models (Maxwell, Kelvin–Voigt). Practical identification and characterization use rheometers that measure stress–strain relationships across varying shear rates and histories.

Applications and considerations span food science, materials processing, pharmaceuticals, cosmetics, and civil engineering, where flow control, stability, and mixing depend on non-Newtonian properties. The term combines the Finnish prefix epä- ("non-" or "un-") with the eponym Newton, referencing the deviation from the simple linear viscous behavior described by Isaac Newton.