Effect of anionic charge quantity on adsorption properties of PCE molecules on ettringite surface: a molecular dynamic simulation method

The adsorption mechanism of superplasticizer molecules on the surface of ettringite was analyzed by molecular dynamic (MD) simulation, and the reasons for the inhibition of ettringite crystal growth by comb-shaped polycarboxylate ether-based (PCE) molecules were revealed. Three methacrylate (MPEG)-based PCEs with different anionic charge amounts were examined in vacuum and solution, respectively. The simulation results of different PCE models were compared, and it was found that there were differences in adsorption conformation, adsorption stability, water density at the interface, migration capacity of water molecules near the surface, and stability of water molecules in PCE membranes. The study found that the interaction between PCEs and ettringite depends on the amount of anion charge. Adding an appropriate amount of anion charge can enhance the interfacial binding energy and make the adsorption of PCEs on the surface of ettringite more compact. However, excessive negative anionic charge at high salt concentrations in solution simulations can change the polymer conformation of the group. By calculating the interfacial density distribution parameters of water molecules, the distance function of PCE molecules and the adsorption on the surface of the model, the MSD and diffusion coefficient of water molecules between layers, and the self-diffusion coefficient and surface adsorption strength of PCEs, it is found that the presence of PCEs not only disturbs the dense water layer above the surface of ettringite, reduces the water density, but also weakens the fluidity of water molecules on the surface of ettringite, slows down the ion exchange rate in the system, and thus inhibits the growth of ettringite crystals.