Molecular Dynamic Simulations for Determining Change in Thermodynamic Properties of Asphaltene and Resin Because of Aging

摘要

In this study, a molecular dynamic (MD) simulation is employed to determine the thermodynamic properties of asphalt binder components, namely, asphaltene and resin, before and after oxidative aging. For oxidative aging of asphaltenes, the percentage of oxygen considered in MD simulations is 0.1,1,12, 23, and 46.5% of asphaltenes. For oxidative aging of resins, the percentage of oxygen used in MD simulations is 5,15, and 25% of resins. Using few oxygen, asphaltene, and resin molecules as input, MD simulations are run on a system at a fixed number of molecules and pressure to predict internal energy, structure, and density as function of the temperature. Simulation outputs are analyzed to determine density, glass-transition temperature, and potential and kinetic energies of the system.- Results show that density has an inverse relationship with the temperature for both asphaltene and resin systems. At high temperatures, asphaltene and resin molecules gain high thermal energy that makes the molecules mobile and capable of breaking molecular association. The density decreases with the increasing temperature because the free volume expands, with or without the association of molecules. The percentage of oxygen affects the glass-transition temperature. At low oxidation levels (<20%). asphaltene shows a constant glass-transition temperature of-5 ℃. At high oxidation levels (>20%), the value of the glass-transition temperature of asphaltene decreases. In resin, no definite relationship between the glass-transition temperature and the oxidation level could be established through the approach used in this study. Finally, changes in potential and kinetic energies of asphaltene and resin because of oxidative aging are discussed.