Cooee bitumen II: Stability of linear asphaltene nanoaggregates

TL;DR

This study uses molecular dynamics simulations and statistical models to analyze the stability and size distribution of linear asphaltene nanoaggregates in bitumen, shedding light on aging-related viscosity changes.

Contribution

It introduces a combined simulation and theoretical approach to quantify nanoaggregate size probabilities, focusing on simplified and complex cases of aromatic molecule aggregation.

Findings

Linear asphaltene nanoaggregates behave as rigid chains.

All aromatic molecules in aggregates behave as flexible chains.

Nanoaggregate size influences bitumen viscosity and aging.

Abstract

Asphaltene and smaller aromatic molecules tend to form linear nanoaggregates in bitumen.Over the years bitumen undergoes chemical aging and during this process, the size of the nanoaggregate increases. This increase is associated with an increase in viscosity and brittleness of the bitumen, eventually leading to road deterioration. This paper focuses on understanding the mechanisms behind nanoaggregate size and stability. We used molecular dynamics simulations to quantify the probability of having a nanoaggregate of a given size in the stationary regime. To model this complicated behavior, we chose first to consider the simple case where only asphaltene molecules are counted in a nanoaggregate. We used a master equation approach and a related statistical mechanics model. The linear asphaltene nanoaggregates behave as a rigid linear chain. The most complicated case where all aromatic molecules are counted in a nanoaggregate is then discussed. The linear aggregates where all aromatic molecules are counted seem to behave as a flexible linear chain.