Initial Stages of Interdiffusion between Asymmetrical Polymeric Layers: Glassy Polycarbonate and Melt Poly(methyl methacrylate) Interface Studied by Neutron Reflectometry

Interfacial evolution of deuterated polycarbonate (dPC) and poly(methyl methacrylate) (PMMA) bilayer films supported on silicon substrates was examined by neutron reflectometry. The dPC was in the glassy state and the PMMA was in the melt state when the samples were annealed at temperatures (from 400 to 415 K) between the bulk glass transition temperature (Tg) of dPC (Tg ∼ 418 K) and PMMA (Tg ∼ 390 K). Asymmetric concentration profiles were observed as a result of composition dependence of the mobility. Once the slow moving dPC molecules leave the dPC-rich side (which was glassy) and enter the PMMA side, the dPC molecules become fast moving and diffuse freely in a viscous melt environment, while the fast moving PMMA molecules become slow as PMMA enter the glassy dPC matrix. Slight change in molecular mass of dPC gives rise to remarkable difference in concentration profile, indicating that mutual diffusion is very sensitive to molecular friction and entanglement of medium. With the penetration of PMMA into...