Small-angle neutron scattering study of onion-type micelles

Full Paper: Onion-type block copolymer micelles were prepared from polystyr ene-block-poly(2-vinylpyridine) (PS-b-PVP) inner micelles in an acidic solu tion by basifying in the presence of poly(2-vinylpyridine)-block-poly(ethyl ene oxide) (PVP-b-PEO). This has the effect of depositing the PVP-b-PEO ont o the collapsed corona of the PS-b-PVP micelle. These core PS-b-PVP micelle s, the small micelles formed by PVP-b-PEO, and the resulting onion micelles were studied by small angle neutron scattering (SANS) techniques. Two rece ntly developed evaluation techniques were employed: 1. Bare-core approximat ion, which utilizes the data at larger scattering angles and provided infor mation about the size and polydispersity of the micelle cores. 2. Applicati on of the Pedersen and Gerstenberg micelle model, which utilizes the whole scattering curve. Due to their polyelectrolyte nature, the core micelles ha d very extended coronas corresponding to rather large statistical segment l engths. The SANS data at large scattering angles for the solution of onion- type micelles revealed the presence of a significant number of the small PV P-b-PEO micelles.: The contribution of the small micelles to the total scat tering was subtracted and the properties and polydispersities of onion core s and stabilizing PEO coronas were obtained. [GRAPHICS]