Non-Newtonian behavior and molecular structure of Cooee bitumen under shear flow: a non-equilibrium molecular dynamics study

TL;DR

This study uses non-equilibrium molecular dynamics to analyze the non-Newtonian shear-thinning behavior and molecular structure of Cooee bitumen, revealing nanoaggregate dynamics and alignment effects under shear at various temperatures.

Contribution

It demonstrates how nanoaggregate size and molecular alignment influence shear viscosity and rheology in a model bitumen, connecting microscopic structure to macroscopic flow behavior.

Findings

Bitumen exhibits shear-thinning at all temperatures.

Nanoaggregate size decreases with increasing shear rate.

Molecular alignment correlates with viscosity changes.

Abstract

The rheology and molecular structure of a model bitumen (Cooee bitumen) under shear are investigated in the non-Newtonian regime using non-equilibrium molecular dynamics simulations. The shear viscosity, normal stress differences and pressure of the bitumen mixture are computed at different shear rates and different temperatures. The model bitumen is shown to be a shear-thinning fluid at all temperatures. In addition, the Cooee model is able to reproduce experimental results showing the formation of nanoaggregates composed of stacks of flat aromatic molecules in bitumen. These nanoaggregates are immersed in a solvent of saturated hydrocarbon molecules. At a fixed temperature, the shear-shinning behavior is related to the inter- and intramolecular alignment of the solvent molecules, but also to the decrease of the average size of the nanoaggregates at high shear rates. The variation of the viscosity with temperature at different shear rates is also related to the size and relative composition of the nanoaggregates. The slight anisotropy of the whole sample due to the nanoaggregates is considered and quantified. Finally, the position of bitumen mixtures in the broad literature of complex systems such as colloidal suspensions, polymer solutions and associating polymer networks is discussed.