Molecular Insights into Glass Transition in Condensed Core Asphaltenes
Glass transition in a condensed core asphaltene model was investigated using molecular dynamics simulations performed in the isobaric–isothermal ensemble. Glass transition temperature obtained from the discontinuities in the slope of specific volume versus temperature plots was in close agreement with experimental results reported in the literature. These discontinuities also correspond to those in isothermal compressibility versus temperature plots. In this paper, we separate the contributions of aliphatic and aromatic regions of the asphaltene molecule to the glass transition behavior. We demonstrate that the aliphatic chains contribute significantly to volumetric changes and impose restrictions to the molecular orientations. Glass transition is accompanied by breaking of π–π stacking of the asphaltene molecule. Therefore, the size of the fused aromatic region in the condensed core determines the strength of intermolecular interactions and the glass transition temperature Tg.