Exploration of molecular dynamics for the adsorption of anionic emulsifier on the main chemical composition surface of aggregate

Abstract

In this study, we conducted molecular simulation and conductivity experiments to systematically explore the adsorption of five anionic emulsifiers on the main chemical composition surface of the aggregate (calcium carbonate: CaCO3, silica: SiO2), which have the same hydrophobic group and different hydrophilic groups. Simulation results and experimental conclusions indicated that the adsorption of the five anionic emulsifiers on the SiO2 surface was stronger than that on the CaCO3 surface. The order of adsorption of the hydrophilic group of the anionic emulsifier on the CaCO3 surface was: benzene sulfonate group (▪) > sulphate group (-OSO3-) > sulfonate group (-SO3-) > diphenyl ether disulfonate group (▪), and that on the SiO2 surface is ▪>-OSO3->-SO3-. These sequences show that the structure of the hydrophilic group of the anionic emulsifier and the degree of branching have an influence on the adsorption of the emulsifier on the CaCO3 and SiO2 surThe adsorption of five anionic emulsifiers on the SiO2 surface is better than faces. The adsorption of anionic emulsifiers on the SiO2 surface is enhanced whereas that on the CaCO3 surface declines with the increase in number of phenyl functional groups. Additionally, the same adsorption characteristics are observed when the branching degree of the hydrophilic group increases. The experimental results fully verified the accuracy of the simulation conclusions. The binding ability of the hydrophilic group of anionic emulsifiers and metal cations is strengthened with an increase in the oxidation of metal cations. Therefore, to avoid early demulsification of emulsified asphalt, it is necessary to prevent the solution from containing a large amount of strong oxidising metal cations under high-mineralization construction conditions. Molecular level micro-information provided by molecular dynamics (MD) can provide guidance for the demulsification of emulsified asphalt and the structural design of the hydrophilic group of the emulsifier.