Energy & Fuels 2008, 22, 3363–3375
3363
Effects of Polymer Modification on Properties and Microstructure of Model Asphalt Systems Liqun Zhang and Michael L. Greenfield* Department of Chemical Engineering, UniVersity of Rhode Island, Kingston, Rhode Island 02881 ReceiVed NoVember 21, 2007. ReVised Manuscript ReceiVed April 18, 2008
Physical properties and microstructures of computational model asphalts were investigated using molecular dynamics simulations in an all-atom framework. A new model asphalt is proposed that is targeted toward core asphalt AAA-1 of the Strategic Highway Research Program (SHRP) based on elemental composition and speciation. Individual compounds were chosen from the literature to represent asphaltene, polar aromatic, naphthene aromatic, and saturate, with interactions ranked using Hansen solubility parameters. The density and thermal expansion coefficient agreed better with experimental data than had predictions using earlier model asphalts. In addition, one polystyrene molecule with 50 repeat units was added into a ternary model asphalt from earlier work and the new six-component AAA-1 model system to analyze polymer modification effects. The expansion coefficient, isothermal compressibility, and their temperature dependence decreased with one polymer chain present, while density increased. Self-diffusion coefficients of each component in both model asphalts decreased upon including the polymer. To assess microstructure, radial distribution functions g(r) of asphaltene and simplified resin molecules were calculated at different temperatures. Asphaltene results changed with temperature and upon including one polymer; artifacts of initial configuration were found at lower temperatures. Radial distribution functions for pairs of resin-like molecules (dimethylnaphthalene, benzoquinoline, and ethylbenzothiophene) and for asphaltene-resin pairs retained similar shapes and first peak positions at different temperatures and when including the polymer. Results for unlike molecules indicated a depletion of resin [g(r)
