Research on the phase structure of Styrene-Butadiene-Styrene modified asphalt based on molecular dynamics

Abstract

To study the phase structure of the SBS modified asphalt by considering the polymer characteristic of liner SBS molecular with different block ratios and concentrations on the molecular scale. A total of 18 molecular dynamics(MD) models were constructed by Gromacs. The phase phenomenon was analyzed by number density and density distribution map. The adsorption behavior of SARA components and SBS were analyzed by considering the SARA molecules' contact characteristics and the adsorption number of SARA molecules on the SBS surface. The result shows that SBS molecular will form the dispersed phase in low concentration (0–4%). With the concentration increasing, the phase will transfer from the dispersed phase to the continuous phase. After the critical concentration, the state of SBS molecule changes from the stable state to the dispersed phase. the SBS with S: B block ratio closer to the middle point is easier to form a continuous phase in different concentrations. The asphaltenes aggregation would also be attracted by SBS, and interact with SBS by branch chains. The saturates molecular is wrapped around the SBS molecules. Resins and aromatics molecules with higher degrees of freedom in space and easy to adjust their spatial structure are also more likely to adsorb around SBS molecules. The highest adsorbed molecules number and molecular weight of different SBS molecules are the Resins, followed by the aromatics. The amount of the adsorbed asphaltenes is nearly the same as that of the saturates. Due to the highest weight of asphaltene molecules in the SARA component, the asphaltene molecular weight absorbed by SBS is close to that of aromatics. The phase structure change may cause a dramatic change in the number of adsorbed molecules.