Shear thinning : determination of zero-shear viscosities from measurements in the non-Newtonian region
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Experimental information on the viscosities, η, of polymer solutions and of polymer melts as a function of shear rate is modeled by means of an approach that describes the diminution of ln η as a function of shear stress, τ, in terms of an exponential decay. The approach uses the following three adjustable parameters: the zero-shear viscosity of the system, a characteristic shear stress, quantifying its susceptibility toward shear thinning, and a dimensionless parameter stating the magnitude of the effect. This procedure gives access to the Newtonian behavior also in cases where direct measurements are impractical or impossible; it discloses two phenomena not reported so far: a qualitative change in the efficacy of τ at a characteristic concentration and indicates the occurrence of two different disentanglement mechanisms in thermodynamically unfavorable solvents.
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Macromolecular chemistry and physics, 221, 14, Wiley-VCH, Weinheim, 2020, https://doi.org/10.1002/macp.202000130