Different Molecular Structures at Polymer/Silane Interfaces Detected by SFG

Buried polymer/silane interfacial molecular structures were examined using sum frequency generation (SFG)vibrational spectroscopy. The silanes under investigation included n-octadecyltrichlorosilane (OTCS), n-octadecyltrimethoxysilane (OTMS), and (3-aminopropyl)trimethoxysilane (ATMS). Poly(methyl methacrylate)(PMMA)and polystyrene (PS)were among the polymers studied, and to avoid spectral confusion, deuterated polymers (d-PMMA and d-PS)were also employed. When OTCS or OTMS contacted a polymer surface, a stable and ordered interface immediately formed. It was found that the silane molecules could adopt different conformations at the interface, depending on the surface structure of the polymer. Such interfacial structures revealed evidence of interfacial molecular interactions at polymer/silane interfaces. Conversely, ATMS molecules tended to become disordered while interacting with the polymer surface, accompanied by the loss of polymer surface order. Through our SFG studies, we demonstrated that by varying the chemistries of both the silane and polymer molecules, the polymer/silane interfacial structures could be altered at the molecular level. Our observations of these different polymer/silane interfaces should further the understanding of the relationships between molecular interfacial structures and properties, such as adhesion.