Interfacial Thermal Transport and Phonon Scattering of Graphene and Graphene Oxide Embedded in Calcium Silicate Hydrate: A Molecular Dynamics Study

Graphene and graphene oxide (GO) are promising nanofillers for improving thermal transport in cementitious materials, but their performance is strongly affected by interactions with calcium silicate hydrate (C-S-H). Understanding how these fillers retain or lose their heat-transport capability after incorporation into the cement hydrate matrix is therefore important for rational nanocomposite design. Reverse non-equilibrium molecular dynamics simulations were conducted to compare isolated graphene/GO sheets with the corresponding sheets embedded in C-S-H. The extrapolated thermal conductivity of pristine graphene decreased from 1854.6 to 1264.2 W/(m·K) after embedding, giving a retention ratio of 0.68. Increasing the oxidation degree reduced the intrinsic conductivity of GO through defect-induced phonon scattering, while the additional reduction caused by C-S-H progressively weakened. At an oxidation degree of 20%, GO retained more than 90% of its isolated-sheet conductivity. Atomic heat-flux analysis showed that C-S-H markedly broadened the transport-direction distribution of graphene but produced only limited additional disturbance in GO. Interfacial binding energy increased with oxidation degree, and radial distribution function analysis identified short-range Ca-O coordination and hydrogen bonding at the GO/C-S-H interface. Phonon density of states analysis further revealed pronounced substrate-induced phonon softening in graphene, whereas the vibrational spectrum of GO remained comparatively stable. These results clarify the trade-off between intrinsic conductivity and matrix-induced thermal stability in graphene-based cementitious nanocomposites.