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Polymers 2017, 9(6), 205; doi:10.3390/polym9060205

Two Ways to Examine Differential Constitutive Equations: Initiated on Steady or Initiated on Unsteady (LAOS) Shear Characteristics

Institute of Hydrodynamics, Academy of Sciences of Czech Republic, Prague 16000, Czech Republic
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Academic Editor: Patrick Underhill
Received: 21 April 2017 / Revised: 29 May 2017 / Accepted: 1 June 2017 / Published: 3 June 2017
(This article belongs to the Special Issue Complex Fluid Rheology)
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Abstract

The exponential Phan–Tien and Tanner (PTT), Giesekus, Leonov, and modified extended Pom–Pom (mXPP) differential constitutive models are evaluated in two ways: with regard to steady shear characteristics and with regard to large amplitude oscillatory shear characteristics of a solution of poly(ethylene oxide) in dimethyl sulfoxide. Efficiency of the models with nonlinear parameters optimized with respect to steady shear measurements is evaluated by their ability to describe large amplitude oscillatory shear (LAOS) characteristics. The reciprocal problem is also analyzed: The nonlinear parameters are optimized with respect to the LAOS measurements, and the models are confronted with the steady shear characteristics. In this case, optimization is based on the LAOS measurements and equal emphasis is placed on both real and imaginary parts of the stress amplitude. The results show that the chosen models are not adequately able to fit the LAOS characteristics if the optimization of nonlinear parameters is based on steady shear measurements. It follows that the optimization of nonlinear parameters is much more responsible if it is carried out with respect to the LAOS data. In this case, when the optimized parameters are used for a description of steady shear characteristics, efficiency of the individual models as documented differs. View Full-Text
Keywords: LAOS; Fourier-Transform rheology; exponential Phan–Tien and Tanner (PTT) model; Giesekus model; Leonov model; modified extended Pom–Pom (mXPP) model; poly(ethylene oxide) LAOS; Fourier-Transform rheology; exponential Phan–Tien and Tanner (PTT) model; Giesekus model; Leonov model; modified extended Pom–Pom (mXPP) model; poly(ethylene oxide)
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Zelenkova, J.; Pivokonsky, R.; Filip, P. Two Ways to Examine Differential Constitutive Equations: Initiated on Steady or Initiated on Unsteady (LAOS) Shear Characteristics. Polymers 2017, 9, 205.

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