Investigation of blend miscibility of a ternary PS/PCHMA/PMMA system using SIMS and mean-field theory

Poly(cyclohexyl methacrylate) (PCHMA) and polystyrene (PS) are miscible with each other, but each is highly immiscible with PMMA. Identifiable by the asymmetries in the binary mean-field interaction parameters χ, PS preferentially segregates to the PCHMA/PMMA interface. Secondary ion mass spectrometry was used to provide real-space depth profiles of deuterated PS (dPS) in a miscible blend with PCHMA. The initial dPS concentration was varied from 5 to 20% (v/v), and the blend film was annealed at 150°C on a film of PMMA for 42 h. X-ray reflectometry was used to determine the interfacial width between PCHMA and PMMA at 150°C. Using self-consistent mean-field theory, good agreement was found between the experimental and theoretical interfacial excess Z* of dPS at each concentration. Because of their similar glass transition temperatures (∼100°C for PS and PCHMA) and the ability of PS and PCHMA to be controllably synthesized with low polydispersities, we anticipate this blend to be a model system for future investigations of such phenomena as diffusion in miscible blends and diffusion near surfaces and interfaces.