Molecular dynamics simulation and experimental study on the influence of hydrophilic group on the adsorption of dodecyl anionic emulsifier on SiO₂ surface

In the process of emulsified asphalt demulsification, the hydrophilic group of the emulsifier molecule is adsorbed on the surface of the aggregate, and the lipophilic group pulls the asphalt droplets to aggregate on the surface of the aggregate to achieve complete demulsification. Therefore, in order to explore the influence of hydrophilic groups of emulsifier on demulsification process of emulsified asphalt, the adsorption of five kinds of anionic emulsifiers with different hydrophobic groups of dodecyl carbon chain and hydrophilic groups on the surface of the main chemical component (SiO₂) of basalt was explored by molecular dynamics and electrical conductivity experiments. The simulation results show that the K⁺ in the hydrophilic group can enhance the van der Waals interaction between the dodecyl anionic emulsifier and water molecules more than Na⁺, and promote the aggregation and adsorption of the dodecyl anionic emulsifier on the SiO₂ surface. The introduction of phenyl functional group into the hydrophilic group can improve the van der Waals interaction between dodecyl anion emulsifier and water molecules and the adsorption capacity of dodecyl anion emulsifier on the surface of SiO₂. The higher the introduction rate of phenyl functional groups, the stronger the van der Waals interaction between the dodecyl anionic emulsifier and water molecules and the stronger the adsorption capacity of the dodecyl anionic emulsifier on the SiO₂ surface. Because of the action of Coulomb force, the diffusion behavior of C atom at the tail end of hydrophobic group and S atom at the polar head of hydrophilic group on the surface of SiO₂ is weaker than that of the five dodecyl anionic emulsifiers. The experimental results show that the adsorption capacity of five kinds of dodecyl anionic emulsifiers on SiO₂ surface increases with the increase of emulsifier concentration and solid/liquid ratio. The order of the adsorption amount of the five anionic emulsifiers on the SiO₂ surface is consistent with the results in molecular dynamics, which verifies the reliability of the conclusion.