On the mechanism of the flow of polymers

TL;DR

This paper proposes a modified mechanism for polymer melt flow that incorporates conformational changes of polymer chains, explaining non-Newtonian viscosity behavior through elastic and entropic effects.

Contribution

It introduces a new model accounting for polymer chain conformational changes and elasticity, extending the classical Eyring formula for non-Newtonian polymer flow.

Findings

Activation energy decreases with shear stress due to chain elasticity.

Conformational changes significantly influence polymer flow behavior.

The model aligns with observed non-Newtonian viscosity characteristics.

Abstract

A non-Newtonian flow of a polymer melt is discussed. The description of the exponential decrease of the apparent viscosity by the well-known Eyring formula with an activation energy reduction proportional to the shear stress does not take into account specific features of the polymeric structure. We propose to modify the description of the macromolecular flow mechanism by including conformational changes of the polymeric chains. The elasticity of a strained polymeric chain, having an entropy origin, can be the reason of the reduction of the activation energy for the transition of a molecular-kinetic unit of the chain into a new equilibrium state in the flow direction during the thermal fluctuation. In that case, the activation energy of the transition should decrease by a value proportional to the reversible high-elastic component of the shear deformation caused by the flow of the polymer.