Scission of flexible polymers in contraction flow: predicting the effects of multiple passages

TL;DR

This study investigates how polymer chains stretch and break during flow through a contraction, providing a predictive model for polymer scission based on flow measurements that are independent of molecular weight and concentration.

Contribution

The paper introduces a geometry-dependent relation to predict polymer scission during successive contractions, separating chain extension effects from scission phenomena.

Findings

Pressure-flux ratio peaks due to polymer extension and scission competition.

Flow rate relation at the maximum is geometry-dependent and molecular weight independent.

Model predicts polymer scission in successive passes through a contraction.

Abstract

When injected through a contraction, high molecular weight polymer solutions exhibit a sharp increase of apparent viscosity which originates from stretching polymer chains above a critical extension rate. This chain stretching can also induce polymer scission, which then decreases the extensional viscosity. In practice, the two phenomena are difficult to separate. Moreover, these phenomena are often observed in situation where flow instabilities appear. In order to disentangle the two effects we have measured the pressure-flux relation for polymer solutions passing through a hyperbolic contraction. The ratio of the pressure drop to that of the (Newtonian) solvent has a maximum due to the competition between polymer extension and scission. We find a geometry-dependent relation between the flow rates at which the maximum occurs for successive passages in a given contraction, which appears to be independent of molecular weight, concentration, solvent quality and viscosity, and can be used to predict the scission under successive passes.