Apparent Fracture in Polymeric Fluids under Step Shear

TL;DR

This paper explains a fracture-like instability observed in entangled polymeric liquids under step shear, attributing it to elastic instability amplified by spatial fluctuations, with a theoretical model matching experimental results.

Contribution

The study applies a modern Doi-Edwards model to quantitatively explain the fracture phenomenon in polymeric fluids, highlighting a distinct elastic instability mechanism.

Findings

Quantitative agreement between theory and experiments

Identification of elastic instability as the cause of fracture

Distinct mechanism from glassy or suspension fractures

Abstract

Recent step strain experiments in well-entangled polymeric liquids demonstrated a bulk fracture-like phenomenon. We have studied this instability using a modern version of the Doi-Edwards theory for entangled polymers, and we find close quantitative agreement with the experiments. The phenomenon occurs because the viscoelastic liquid is sheared into a rubbery state that possesses an elastic constitutive instability (Marrucci and Grizzuti, 1983). The fracture is a transient manifestation of this instability, which relies on the amplification of spatially inhomogeneous fluctuations. This mechanism differs from fracture in glassy materials and dense suspensions.