Effect of temperature on NaCl migration properties within nano-channels of graphene, graphene oxide, and nano-silica modified cementitious composites: A molecular dynamics study

Organic coatings at different temperatures exhibit different diffusion behaviors under the attack of salt solutions. The present study investigates the transport processes and erosion mechanisms of NaCl solutions within the channels of calcium silicate hydrated (C-S-H), C-S-H branched graphene (Gr), functionalized graphene oxide (GO-O, GO-OH and GO-COOH) and 2D-silica (NS) at different temperatures (250 K–400 K) by molecular dynamics. The results obtained demonstrate that the NaCl solution exhibits a half-crescent shape transport in the C-S-H channels and that the solution can pass through the nano-channels at a faster rate as the temperature increases. Elevated temperature increases diffusion, which weakens the bonding strength between the nanomaterials and C-S-H. Gr exhibits a strong repulsion of water and ions. GO-O gradually separates from the C-S-H surface with increasing temperature, proving that its interaction with C-S-H is slowly weakened. Aggregation of NS occurs, forming larger particles to reduce fluidity, and increasing temperature helps to increase diffusion. Oxygen in GO-OH and GO-COOH readily accepts hydrogen bonds and binds to sodium ions, thus immobilizing ions and water molecules on the GO surface. As the temperature increases, the distance of hydrogen bonding increases, but the RDF peak increases, showing that the intermolecular interactions remain strong, which enhances the hydrophilicity of the material. Density Functional Theory (DFT) studies have shown that the adsorption of Ca²⁺, Na⁺, H₂O and Cl⁻ by Gr, GO and NS are Ca²⁺>Na⁺>H₂O > Cl⁻.The rate of diffusion of water shows a different order with temperature in various materials, especially at high temperatures where certain materials have better diffusion properties. The dissociation of water molecules and Ca²⁺ increases with increasing temperature, leading to a decrease in the binding strength between C-S-H and the nanomaterials. The study in this paper will help to reveal the subtle mechanisms of capillary transport in C-S-H nanopores at different temperatures, thus providing a more scientific basis for the design and optimization of cementitious materials. With a better understanding of these mechanisms, we can further promote the development of advanced cementitious materials and enhance their performance and durability in engineering applications.