"Volume preserving" rheological models for polymer melts and solutions using the GENERIC formalism

A constrained theological model for polymer solutions and melts is develope d using the GENERIC formulation. The constraint, det c = constant, where c is a conformation tensor, is introduced in the general formulation using a modified mobility tenser, Lambda(1), and a Helmholtz free-energy function e xpressed in terms of the scaled invariants of the conformation tenser. The predictions of this family of' "volume-preserving" models are illustrated f or a modified Hookean energy function and several expressions of the modifi ed mobility tenser. The predictions are compared to experimental data taken from the literature for polymer melts and polymer solutions. The sensitivi ty of the predictions to model parameters (a maximum of four fdr this parti cular case) shows that in steady and transient shear flows, it is possible to cover a wide range of theological behaviors generally observed for polym er melts and solutions.;Comparison with experimental results for polymer me lts and solutions shows that the model predicts very well the steady shear viscosity and first normal stress coefficient behavior for an extended rang e of shear rates. Model predictions for material functions in shear start-u p experiments compare fairly well with the experimental data. The modified Hookean energy function proposed to illustrate the approach is found to giv e larger overshoots than those observed experimentally in sheer start-up ex periments. Predictions for shear stress relaxation failed to compare with t he set of experimental data for which this property is available. It is bel ieved that these drawbacks with this particular choice of the Helmholtz fre e-energy function can be overcome using multiple conformation variables. Th is can be easily done in this formulation. (C) 1999 The Society of Rheology . [S0148-6055(99)00801-9].