Zero-shear rate viscosity from creep compliance

Strain from a creep experiment with constant applied stress a for a viscoelastic solid (lower curve) and a viscoelastic liquid (upper curve). The slope at long times is the steady shear rate 7, from which the viscosity is calculated as = cr/7 (the viscosity of any solid is infinite, corresponding to zero slope). The extrapolation of this straight line to zero time (dotted line) gives the elastic part of the strain, from which the recoverable compliance is determined. 

Two quantities that play important roles in flow behavior of polymeric liquids are the steady-state viscosity at zero shear rate, rto, and the steady-state recoverable shear compliance, J°. Both are obtained quite directly from creep results, from (To and the shear rate fss in the steady-state region of the creep phase and J° from the total recoil strain (yr) in the recovery phase ... 

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