Profiling Pvp/Ps Homopolymer Interfaces Using Core-Loss Electron Energy-Loss Spectroscopy

Despite the physical and technological significance of polymer interfaces (1), they have not been extensively studied using techniques based on electron scattering. Spontak et al. (2) used digital analysis of bright-field images to study Os-stained polystyrene-polydiene block copolymer interfaces, but work in this area has been lacking largely because of difficulties with staining or uncertainties in the distribution of stain at the nanometer length scales relevant to interfaces. Studies of polymer interfaces are now largely done by neutron scattering (3) This research explores the application of spatially-resolved electron energyloss spectroscopy to measure compositional widths of polymer-polymer interfaces. These first studies focus on blends of poly(2-vinyl pyridine) (PVP) dispersed in poly(styrene) (PS) to establish the various electron-optical, electron-scattering, and specimen-dependent limitations (4) to resolving such an interfacial width. The uncompatibilized PS/PVP interface should be relatively sharp. Blends of PS (M.W. 190,000) and PVP (M.W. 200,000) were made using a 5wt% solution of polymer in THF with a PS/PVP ratio of 7/3. The solution was cast into methanol. The resulting solid precipitate was removed and annealed under vacuum at 120°C for 36 hours.