# Molecular Dynamics-Based Study of Graphene/Asphal Mechanism of Interaction
## 1 Introduction  
With the development of nanotechnology, nanomaterial-modified asphalt is increasingly being widely used in road construction. Researchers have tried to add a variety of nanomaterials such as nano-zno, nano-clay, nano-TiO\({}_{2}\), nano-CaCO\({}_{3}\), nano-SiO\({}_{2}\), graphene, and graphene oxide to the asphalt and mix to strengthen the mechanical properties of the pavement, aging resistance, fatigue resistance, adhesion properties, etc. [1; 2; 3; 4; 5]. Compared with other nanomaterials, graphene has a large specific surface area, excellent physical properties (mechanical, thermal, optical), and stable chemical structure [6; 7; 8] while having significant \"small size effects\", \"quantum size effects\", and \"surface and boundary effects\" [9; 10; 11]. It has been proved that the binder's mechanical strength, aging resistance, and high-temperature stability can be significantly improved by introducing graphene nanosheets into asphalt material. In particular, using graphene composite rubber powder as a new modifier has attracted extensive attention to improving the storage stability, high-temperature rutting performance, and aging performance of asphalt adhesives [12; 13]. On the other hand, graphene tends to agglomerate and accumulate, which is not conduciveto its large-scale application [8], and the interaction mechanism between graphene and asphalt binders is still unclear. In recent years, molecular dynamics simulation methods have been widely used to explore the mechanism of asphalt-aggregate interface interaction [14], asphalt aging [15], and asphalt self-healing [16] and have made breakthrough progress. Molecular dynamics (MD) simulation, as a kind of computerized virtual simulation test, can break through the limitations of traditional testing instruments, effectively make up for the shortcomings of macroscopic tests, and reveal the microscopic mechanisms of the macroscopic properties of asphalt from the molecular or even atomic scale [17; 18]. [PERSON] et al. [17] explored the adhesion properties and interaction behavior between graphene and asphalt four components (SARA) and aggregate with the help of the molecular dynamics (MD) simulation method; the simulation results showed that the adhesion work between asphaltene and aromatic fractions and GNPs was 30% higher than that of colloidal and saturated fractions. However, adding GNPs did not significantly affect the adhesion enhancement between asphalt and aggregate. [PERSON] et al. [19] used molecular dynamics to comparatively evaluate the adhesion behaviors between CNTs, GNPs with aggregates, and SARA, and the simulation results showed that the interfacial strength and adhesion work between GNPs and SARA was higher than that between CNTs and SARA, where the CNTs-SARA interfacial interactions were mainly achieved through van der Waals forces. [PERSON] et al. [11] found through MD simulations that hydrogen binding plays a vital role in the reinforcement of asphalt nanocomposites; significantly modified graphene (hydroxylated and epoxy-modified) can form more robust interactions with the polar components of asphalt, which improves the shear resistance. [PERSON] [20] further verified the binding relationship between the four elements of asphalt and the GOs based on density-functional theory (DFT) calculations, and the results showed that the gums were most stabilized with the GOs. In addition, GOs can effectively hinder the movement of saturated fractions and enhance the high-temperature stability and thermal aging resistance of asphalt; GOs are uniformly and stably dispersed in the asphalt matrix mainly through non-chemical binding. With the help of molecular dynamics simulation, [PERSON] et al. [18] found that GOs have the potential to enhance the performance of SBS-modified asphalt by reducing the diffusion coefficient of the molecules, enhancing the strength of the three-dimensional network structure of SBS-modified asphalt, and thus improving its ability to resist permanent deformation.