Nano-adhesion behavior and failure mechanisms of polymer cement-based materials at high temperature

Molecular dynamics simulations were performed to investigate the interfacial adhesion behavior between polymers and cement-based material substrates. Three kinds of polymers were constructed and validated based on literature reviews, ethylene-vinyl acetate (EVA), styrene-acrylate (SAE), and styrene-butadiene (SB) copolymers, respectively. The molecular modeling of the cement-based materials was constructed by means of its two main components, calcium silicate hydrate (C-S-H) and silicon dioxide (SiO₂). C-S-H-polymer-C-S-H and C-S-H-polymer-SiO₂ composite structures under uniaxial tension were simulated at ambient temperature of 300 K, 350 K, and 400 K, respectively. The results reveal that the polar functional groups in EVA and SAE polymers form coordination bonds and H-bonds with C-S-H/SiO₂, thereby enhancing the adhesion of these two polymers to the substrate. As for the SB polymer without polar functional groups, the C_(CC) atoms form weak electrostatic interactions with the Ca atoms on the surface of C-S-H. In addition, with increasing temperature, (i) the number and the stability of the coordination and H-bonds formed between EVA and C-S-H/SiO₂ decreased, leading to a decrease in adhesion, (ii) the electrostatic interaction between SB and C-S-H weakened, which also led to a decrease in adhesion, and (iii) the COO^- group was gradually formed through hydrolysis of SAE, thereby improving the adhesion performance.