Viscoelastic Phase Separation in Shear Flow

TL;DR

This paper uses numerical simulations to explore how viscoelastic phase separation in polymer solutions behaves under shear flow, revealing complex stress dynamics and domain structures.

Contribution

It introduces a coupled two-fluid model with a conformation tensor to study shear-induced phase separation and stress behavior in polymer solutions.

Findings

Steady two-phase states with domain size inversely proportional to shear stress

Enhanced heterogeneity in composition and viscoelasticity under shear

Transient negative normal stress differences observed

Abstract

We numerically investigate viscoelastic phase separation in polymer solutions under shear using a time-dependent Ginzburg-Landau model. The gross variables in our model are the polymer volume fraction and a conformation tensor. The latter represents chain deformations and relaxes slowly on the rheological time giving rise to a large viscoelastic stress. The polymer and the solvent obey two-fluid dynamics in which the viscoelastic stress acts asymmetrically on the polymer and, as a result, the stress and the diffusion are dynamically coupled. Below the coexistence curve, interfaces appear with increasing the quench depth and the solvent regions act as a lubricant. In these cases the composition heterogeneity causes more enhanced viscoelastic heterogeneity and the macroscopic stress is decreased at fixed applied shear rate. We find steady two-phase states composed of the polymer-rich and solvent-rich regions, where the characteristic domain size is inversely proportional to the average shear stress for various shear rates. The deviatoric stress components exhibit large temporal fluctuations. The normal stress difference can take negative values transiently at weak shear.