Molecular Modeling of Capillary Transport in the Nanometer Pore of Nanocomposite of Cement Hydrate and Graphene/GO

The excellent impermeable nature of graphene-based nanomaterial makes it a potential membrane to repel detrimental ion invasion. To evaluate the ion-resisting properties by different graphene materials, molecular dynamics is utilized to investigate the water and ion transport in a nanometer channel of the calcium silicate hydrate (C-S-H) substrate impregnated with a single-layer graphene sheet and graphene oxide (GO) sheet functionalized by hydroxyl and carboxyl (GO-OH, GO-COOH). The transport rate and diffusivity of fluid is greatly dependent on the types of functional groups in the coating sheet. The van der Waals interaction between graphene sheet and C-S-H gel is weakened dramatically by the invading of ions and water molecules, resulting in the dissociation of graphene sheet from the C-S-H surface. The detached graphene sheet contributes little to repelling water and ions. On the other hand, the hydroxyl and carboxyl groups in the GO sheets provide plenty of oxygen sites to accept the H-bonds and to associate with the neighboring sodium ions, which immobilizes the water molecules and ions on the GO surface. The GO-COOH sheets, deeply rooted on the C-S-H, further block the transport channel connectivity and "cage" the water and ions in the entrance region of gel pore. Hopefully, this study can provide valuable insights into the design of the GO membrane to enhance water resistance for sustainable cementitious composites.