Molecular dynamics modeling of the interface between surface functionalized graphitic structures and calcium-silicate-hydrate: interaction energies, structure, and dynamics.

Molecular dynamics simulations were performed to study the molecular-scale energetic, structural, and dynamic properties of the interface between surface functionalized graphitic structures and calcium-silicate-hydrate (C-S-H). The 9 A tobermorite structure was used as a model for C-S-H, the main building block ("the glue") that hold a cementitious matrix together. Six types of carbon surface structures were investigated: a pristine graphite plane and five graphite planes functionalized with hydroxyl (OH), carboxyl (COOH), carboxylate (COO(-), deprotonated carboxyl), carbonyl (CO), and amine (NH(2)) groups. Results demonstrated the dominant role of electrostatic forces in the interfacial interactions and indicated that the polarity of the functional group can be used as an indicator of affinity to C-S-H. MD simulations revealed that an optimal number of polar oxygen containing groups may exist for efficient graphitic structure/cement interaction and emphasized the mediating role of Ca(2+) counterions in the interfacial interactions.