Intermolecular Forces between Nanolayers of Crystalline Calcium-Silicate-Hydrates in Aqueous Medium

Calcium-silicate-hydrate (C–S–H) is the major binding phase responsible for strength and durability of cementitious materials. The cohesive properties of C–S–H are directly related to the intermolecular forces between its layers at the nanoscale. Here, we employ free energy perturbation theory (FEP) to calculate intermolecular forces between crystalline C–S–H layers solvated in aqueous medium along face-to-face (FTF) and sliding reaction coordinates. Contrary to mean-field theories, we find that our counterion-only system exhibits an oscillatory behavior in FTF interaction. We correlate these oscillations with the characteristic length scale comparable to the distance between interfacial water layers at the hydrophilic surface of crystalline C–S–H. We attribute the sliding intermolecular forces to the atomic level roughness of crystalline C–S–H layers stemming from the local arrangement of nanoscale structural motifs. These intermolecular forces provide a direct access to the key mechanical properties, such as surface energy, cohesive pressure and elastic properties. The simulation results are in close agreement with the available experimental measurements. Furthermore, we present these intermolecular forces in a mathematical framework to facilitate coarse-grain modeling of crystalline C–S–H layers. These results provide a novel route that paves the way for developing realistic mesoscale models to explore the origins of chemophysical properties of crystalline C–S–H.