Molecular Insights into Structural, Dynamical, Thermomechanical, and Rheological Properties of Graphene-Reinforced...

Unraveling the subtle role of molecular interactions controlling the rheological and thermomechanical responses of graphene-reinforced asphalt binders using molecular dynamics (MD) simulations is a cornerstone problem in statistical thermodynamics because of its chemical heterogeneity, nonergodicity, and sluggish dynamics associated with viscoelastic relaxation. Herein, we emphasize devising generalized models of asphalt binders, resolving finite size effects and phase separation during thermodynamic equilibration of large-scale models, and quantitatively assessing diverse structural and dynamical properties including density, solubility parameter, diffusivity, viscosity, mechanical, and thermophysical properties of pristine asphalt and graphene-modified binders. This study provides a molecular framework for optimizing the thermodynamic compatibility between asphalt components and graphene nanofiller and enhancing thermomechanical properties by tailoring filler percentages. The uniaxial deformation simulations performed at different strain rates demonstrate that the yield stress and postyield softening can be improved just by adding 2 wt. % of graphene filler. The increased toughness in graphene-modified binders strongly correlates with the predicted higher noncovalent intermolecular forces, lower diffusivity of asphalt components, and increased zero-shear equilibrium viscosity compared to the pristine asphalt. The glass transition temperature of asphalt is enhanced by about 26 K for the 2 wt. % graphene-reinforced asphalt composite. Density functional theory (DFT), natural energy decomposition analysis (NEDA), noncovalent interaction (NCI) analysis, and steered molecular dynamics (SMD) simulations were employed to probe the molecular mechanisms governing graphene-asphalt interactions. The multiscale simulations reveal that the strong interfacial interactions between graphene and polar asphalt components, dominated by π-π stacking and dispersion forces, are responsible for the mechanical reinforcement of the asphalt matrix. The resemblance of predicted data with experimental results in many cases further substantiates the applicability of a theoretical framework for the rational design of graphene-modified asphalt binders with desired physicochemical properties.