Solid state NMR investigation of γ-irradiated composite siloxanes: Probing the silica/polysiloxane interface

We employ silicon-proton (29Si{1H}) cross polarization magic-angle spinning (CP-MAS) to probe directly the interface of a silica-filled polysiloxane elastomer subjected to gamma radiation. Using a traditional spin-lock CP experiment in conjunction with a silicon-edited proton rotating-frame longitudinal relaxation sequence, the full suite of CP build-up parameters are extracted for six resolvable silicon chemical shifts. The data, represented by three parameters, THX, T1ρH, and M∞, are interpreted by means of a model where the simultaneous effects of silica surface hydroxyl modification, interfacial water content, and radiation-induced chemistries are considered responsible for the observed macroscopic behavior of these engineering materials.