Analyzing properties of model asphalts using molecular simulation

Molecular simulations have been used to estimate the properties of three-component mixtures whose constituents were chosen to represent the chemical families found in paving asphalts. Naphthene aromatics and saturates were represented by 1,7-dimethylnaphthalene and n-C-22, respectively. Two different asphaltene model structures were considered. The first has a large aromatic core with a few short side chains; the second contains a moderate size aromatic core with larger branches. Both types have been proposed in the recent literature based on experimental characterizations of asphaltene fractions. Properties calculated from atomistic molecular simulations of the mixtures include density and isothermal compressibility (inverse of bulk modulus). The thermodynamic properties suggest a high-frequency glass transition above 25 degrees C for both model mixtures. The mixture based on the more aromatic asphaltene shows a more pronounced transition and has a higher bulk modulus. For a polymer-modified model asphalt, the calculations are consistent with increases in the bulk modulus.