Molecular dynamics study on ultra-confined NaCl solution in the silane coupling agent modified rubber calcium silicate hydrate nano-pore

Abstract

The corrosive ions in the coastal environment invade the rubber concrete structure through capillary adsorption, which greatly limits the reuse of waste rubber. Silane coupling agent (SCA) modified rubber concrete gradually enters people's field of vision due to the improvement of its mechanical properties, and at the same time, it helps to improve the durability of the material. However, the interaction mechanism of action of ions with SCA and rubber is still unclear. Based on molecular dynamics theory, this study simulates the NaCl solution in the pores of C-S-H gel and rubber before and after SCA modification. Through the analysis of the local structure and dynamic performance of water molecules and ions, it is found that the direction of the distribution of water molecules at the rubber interface is opposite to that of C-S-H. The order of water molecules on the silane interface is enhanced, and it has a richer hydrogen bond network. The hydrophobicity of rubber has been confirmed on a microscopic scale, while silane has a duality to water molecules. The silanol group close to the C-S-H substrate is hydrophilic and can form hydrogen bonds with water molecules, while the tail alkane group is highly hydrophobic. Moreover, rubber and silane are not conducive to the adsorption of Na+ and Cl- and will change the coordination of ions at the interface. Although there are many kinds of hydrogen bonds between silane and water molecules, the stability is poor. The addition of silane will slow down the movement speed of water molecules in the pores, thereby indirectly improving the resistance of the SCA modified rubber cement-based material to corrosion by chloride ions.