Fluids non-Newtonian time-dependent

Basic Protocol 2 is for time-dependent non-Newtonian fluids. This type of test is typically only compatible with rheometers that have steady-state conditions built into the control software. This test is known as an equilibrium flow test and may be performed as a function of shear rate or shear stress. If controlled shear stress is used, the zero-shear viscosity may be seen as a clear plateau in the data. If controlled shear rate is used, this zone may not be clearly delineated. Logarithmic plots of viscosity versus shear rate are typically presented, and the Cross or Carreau-Yasuda models are used to fit the data. If a partial flow curve is generated, then subset models such as the Williamson, Sisko, or Power Law models are used (unithi.i). 

Fluids that do not obey Newton s law of viscosity can be broadly grouped into time-independent and time-dependent non-Newtonian fluids. Subclassifications for each group are convenient (3). 

Time-Dependent Non-Newtonian Fluids. Time-dependent non-Newtonian fluids are characterized by the property that their viscosities are a function of both shear rate and shear history. 

Time dependent non-Newtonian fluids show a change in viscosity with time under constant shear rate. They are further classified as thixotropic, showing decrease in viscosity with time, and as rheopectic, showing an increase in viscosity with time at constant shear rate. 

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