안혜진  장갑식  송기원

54권  4호, pp. 253-267, 8월  2017
10.12772/TSE.2017.54.253

viscoelastic polymer liquid large amplitude oscillatory shear (LAOS) Doi-Edwards constitutive equation Wagner model Lissajous pattern (stress-strain rate hysteresis loop) nonlinear viscoelastic function

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The present study has been designed to predict the nonlinear viscoelastic behavior of concentrated polymer systems in large amplitude oscillatory shear (LAOS) flow fields by means of the Doi-Edwards constitutive equation. Using an Advanced Rheometric Expansion System (ARES), the dynamic viscoelastic behavior of aqueous poly (ethylene oxide) (PEO) solutions with various molecular weights and different concentrations has been investigated with a various combination of several fixed strain amplitudes and constant angular frequencies. The linear dynamic data (storage modulus and loss modulus) over a wide range of angular frequencies were also obtained to determine the relaxation spectrum parameters. The experimentally obtained Lissajous patterns (stress-strain rate hysteresis loops) were compared with the Doi-Edwards model predictions over a wide range of strain amplitudes and angular frequencies for all polymer solutions prepared in this work. The nonlinear viscoelastic functions were analyzed by the aid of 3D plots and predicted over a wide range of strain amplitudes to evaluate the overall predictability of the Doi-Edwards model. The main findings obtained from this study are summarized as follows: (1) The Lissajous patterns predicted by the Doi-Edwards model represent a good agreement with the experimentally obtained stress-strain rate hysteresis loops both in linear and nonlinear viscoelastic regions. (2) The predictions of the Doi-Edwards model are closely coincident with the experimental results in the linear viscoelastic region. As the strain amplitude is increased, the predicted nonlinear viscoelastic functions are somewhat larger than that of the experimental data. Nevertheless, all trends of the nonlinear viscoelastic behavior are qualitatively in good agreement with the experimental results. (3) The Doi-Edwards model gives a very good prediction for the first harmonic storage modulus and loss modulus up to the nonlinear viscoelastic region. The third and fifth harmonic storage and loss moduli exhibit an overshoot or an undershoot at large strain amplitudes. This constitutive equation can describe well such excessive behavioral changes in a qualitative sense. (4) The Doi-Edwards model has a slightly better ability than the Wagner model to predict the LAOS flow behavior of concentrated polymer systems.