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Shear Thinning: Determination of Zero‐Shear Viscosities from Measurements in the Non‐Newtonian Region
Author(s) -
Wolf Bernhard A.
Publication year - 2020
Publication title -
macromolecular chemistry and physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.57
H-Index - 112
eISSN - 1521-3935
pISSN - 1022-1352
DOI - 10.1002/macp.202000130
Subject(s) - shear thinning , dimensionless quantity , shear (geology) , shear rate , thermodynamics , newtonian fluid , exponential function , shear stress , viscosity , materials science , non newtonian fluid , polymer , mechanics , chemistry , composite material , physics , mathematics , mathematical analysis
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.