Atomistic study on silica-based superhydrophobic material interaction with calcium ion in concrete industry

The interaction between calcium ions and hydrophobic silica-based material plays a critical role in understanding the durability and interfacial properties of protective coatings within concrete. In this study, Density Functional Theory (DFT) computations are utilized to investigate the interaction between calcium ions and model compounds within a silica-based hydrophobic material. These model compounds include 3-aminopropyltriethoxysilane (APTES), triethoxy(octyl)silane, Bisphenol A, and silicon dioxide. Geometry optimizations and electronic structure computations are carried out for these model compounds. The DFT computations are performed with the B3LYP/6-311++G(d,p) method with Grimme’s D3 correction. Molecular Electrostatic Potential (MEP), Reduced Density Gradient (RDG), and Non-Covalent Interaction (NCI) analyses are performed to investigate the charge distribution and intermolecular interactions. The results obtained from DFT computations show that calcium ion stabilization increases progressively from isolated organic modifiers to a complex silica-based material. While APTES, Bisphenol A, and triethoxy(octyl)silane make a contribution to calcium ion stabilization by weak to moderate intermolecular interactions, silicon dioxide shows the strongest interaction with calcium ions. Silicon dioxide seems to be the major contributor to calcium ion stabilization. However, the strong interaction between calcium ions and water points to hydration as a major competing effect.