For systems showing non-Newtonian behaviour when measured in steady simple shear, a coefficient η equal to σ D at a given value of the shear rate D, where σ is the stress; η 0 is the limiting viscosity at zero shear rate, and η ∞ the limiting viscosity at infinite shear rate; [η0] is the limit of intrinsic viscosity at zero shear.
Source:
PAC, 1979, 51, 1213. 'Terminology and Symbols in Colloid and Surface Chemistry Part 1.13. Definitions, Terminology and Symbols for Rheological Properties' on page 1217 (https://doi.org/10.1351/pac197951051213)