▎ 摘　　要

In this study, a novel graphene oxide (GO) and epoxy (EP) composite coating was proposed to prevent the ingress of the water and ions in the nanometer channel of calcium silicate hydrate (C-S-H) gel. To evaluate the water resisting properties of the GO-EP composite coating, the local structure, dynamic properties and water transport mechanism have been studied by molecular dynamic method. As compared with single coating with graphene oxide, the migration of water and ions is significantly inhibited in the C-S-H gel pore impregnated with GO and hydrophobic epoxy composite. The GO plays critical role in bridging the C-S-H gel and epoxy composite. The functional groups in the GO sheets associate with the interfacial calcium atoms in the interior surface of C-S-H gel and provide oxygen sites to accept the H-bonds from the silicate tetrahedron. On the other hand, the H-bonds donated by the hydroxyl in the GO sheets to epoxy help strengthen the connection between the GO sheets and epoxy molecules. During the capillary transport process, the water molecules are firstly dragged by the hydroxyl groups on the GO sheets, accept or donate their H-bonds to functional groups and diffuse in the vacancy region between epoxy molecules and GO sheet. The hydrophobic epoxy molecules, blocking the C-S-H gel pore, inhibit the solution invasion. With the coating percentage of epoxy molecules from 21.8% to 87.2%, the gyration radium of molecule increase from 10.42 to 10.52 and the penetration depth of water molecules is dramatically slowed down by 71.58%. While the penetrated solution results in the reduction of adhesive energy by 66.38% between GO sheets and epoxy group, the adhesive energy between GO and C-S-H remains constant. The incorporation of GO sheet between C-S-H and epoxy can contribute to the stability of the composite coating. Furthermore, the mobility of Na and Cl ions is reduced due to the presence of the GO-EP composite coating, which immobilizes the penetrated Na and Cl ions in the entrance region and separates the ions from the water solution. Hopefully, the novel hydrophilc-hydrophobic composite coating provides valuable insights on the design of waterproof material.