Polymer Enhancement Mechanisms in Cementitious Materials: Insights from Atomistic Simulation

The mechanical properties of organic/inorganic composites at a macroscopic level are largely determined by the interaction mechanisms at the interface. However, there have been limited microscopic studies on these interactions. To address this knowledge gap, this study used molecular dynamics (MD) simulation to examine the interfacial structures, kinetics, and energetics between calcium silicate hydrate (CSH) and polymers. The purpose of this investigation is to shed light on the factors contributing to the variations in mechanical properties of the materials and to provide atomic-level guidance for nanocomposite toughening studies. Three polymers, polyacrylamide (PAM), sodium polyacrylate (PAAS), and polymethacrylic acid sodium sulfonate (PAMAS), were incorporated into the nanochannels of CSH sheets to create polymer/calcium silicate hydrated composites. Our simulations revealed that calcium atoms at the CSH surface act as intermediaries bridging polymers and the CSH through Ob─ Casur─ Op and metal atoms in polymer functional groups through Ob─ M─ Op. Furthermore, hydrogen bonds between the interface water molecules and the polymer and CSH matrix were observed through Op─ Casur─ H2O─ Ob and Op─ M─ H2O─ Ob bonds. Uniaxial tensile simulations were carried out to assess the mechanical behavior of composites, with results indicating that all three materials failed at their interfaces. Analysis of chemical bonding at the point of failure revealed that PAM/CSH exhibits the highest number and stability of chemical bonds and thus the best mechanical properties, followed by PAAS/CSH, with the worst being PAMAS/CSH. Our study provides fundamental atomic-level insights into the differences in interaction mechanisms and macroscopic mechanical properties of composites through molecular dynamics simulation, offering a theoretical basis for polymer modification of CSH and the genetic improvement of cementitious materials.