Unraveling the influencing mechanism of water ingress on the adhesion behavior of poly(dimethylsiloxane)-silica interface: a molecular dynamic study

Water ingress in nanofiller reinforced polymer nanocomposite is usually considered as one of the causes for the interfacial failure between nanofiller and nanocomposite. However, the molecular mechanism for the effects of water on the interfacial adhesion behavior has rarely been studied. In this work, atomic scale interfacial adhesion behavior of silica nanoparticles reinforced poly(dimethylsiloxane) (PDMS) matrix was studied by using molecular dynamics (MD) simulations. Moreover, the influences of silica wettability and terminal groups of PDMS molecules on their interfacial adhesion behavior were also investigated. The results show that the hydrophilic silica has stronger interfacial adhesion force in PDMS matrix with hydroxyl terminated PDMS molecules due to the strong interfacial van der Waals, electrostatic and hydrogen bonds interactions. After water ingress, the invaded water can be adsorbed at the interface and weaken the adhesion strength, especially for the hydroxyl modified silica system. As for the PDMS system with hydroxyl terminated groups, the invaded water molecules are inclined to transport in the PDMS matrix instead of adsorb at the interface. This work provides a new method to investigate the interfacial adhesion behavior of nanofillers in resin matrix at molecular level by using MD simulations, and also proposes some principles to obtain stronger adhesion strength of nanofillers in polymer matrix by tuning their hydrophilicity according to the application environment.