Interface instabilities and chaotic rheological responses in binary polymer mixtures under shear flow

Abstract

A unified model by combining the Rolie–Poly constitutive model and the Flory–Huggins mixing free energy functional through a two fluid approach is presented for studying flow-induced phase separation in polymer mixtures. It is numerically solved in two-dimensional flow with monotonic and non-monotonic constitutive behaviour. The results are analyzed and show that this model can capture the essential dynamic features of viscoelastic phase separation reported in literature. The steady-state shear-banding and interface instabilities are reproduced. In the case with a non-monotonic constitutive behaviour, It is observed that the band structures are strongly unstable both in time and in space. The correlations between the microstructure evolution and chaotic rheological responses have been identified. A vortex structure emerges within the central band. Numerical results obtained from this study suggest that the dynamic features of rheochaos can be captured by the proposed model without introducing extra parameters.