Systematic study of the effect of silane coupling agent on the hydrothermal aging resistance of the underfill epoxy resin and silica interface via molecular dynamics simulation

Abstract

Molecular dynamics simulations are used to elucidate the mechanism by which silane coupling agents (SCAs) affect the hydrothermal aging resistance of the epoxy resin (EP)/silica interface, which is the main type of interface existed in/around the underfill adhesive (UF). A hybrid model is constructed based on the amorphous silica surface, and two types of reactive SCA (i.e. the epoxy-functionalized SCA 1 and the amine-functionalized SCA 2) are chemically introduced. In this study, microscopic interfacial structures and properties for unaged and aged conditions are evaluated and compared. We find that both SCAs can enhance the interfacial energies between EP and the silica surface, which consequently increases the stability at the interfaces under hydrothermal aging conditions. The covalent contribution in SCA 2 is significantly higher than in SCA 1, which is a principal factor contributing to the stabilization of the interface. Therefore, both SCA can be taken as effective “springs” that connect the EP and silica surface. Moreover, SCA 1 can be taken as longer but flexural “springs” with lower spring constant, which also reduces the interfacial density of EP and allow for greater water ingress; while SCA 2 can be taken as shorter but straight “springs” with higher spring constant, which significantly reinforce the interface. These findings provide us microscopic insights into the impact of SCA on the EP/silica surface, which could be helpful in the selection of more effective SCAs that improve the hydrothermal aging resistance of UF.