Interfacial Stability and Confined Structures for Graphene/SiO₂ Composites in Water Media

Isolated monolayer graphene can be coupled with silica (SiO₂) as graphene-based nanoelectronic devices. The fabricated heterojunction composites in moist environments have been involved in environmental monitoring, optical detection, and health sensors. However, the corresponding interfacial stability and structures between graphene and silica substrates remain unexplored. Herein, molecular simulations were applied to investigate the adhesion of graphene/SiO₂ composite interfaces in water media. Different SiO₂ surface types and varied SiO₂ hydrophilicity degrees were considered. The thermodynamic free energy was simulated to characterize the interfacial interaction. The required energetic barriers associated with the graphene detachment can be determined. SiO₂ substrates possess differential surface affinity toward graphene. The connection between the adhesion strength and the substrate types was established. Under higher hydrophilic conditions, the attached graphene sheet can easily be separated from the silica substrates. This behavior cannot be observed in dry conditions, which is attributed to competitive actions between the interfacial hydration force and the substrate interaction. The morphologic transformations and hydration structures of the graphene-silica interface with intervening water layers were also characterized, which is critical in modulating the interface stability. Our simulation results provide new microscopic insights into the interfacial states and structures of graphene-SiO₂ systems in an aqueous environment.