Atomic Force Microscopy and Light Scattering Study of Onion-Type Micelles Formed by Polystyrene-block-poly(2-vinylpyridine) and Poly(2-vinylpyridine)-block-poly(ethylene oxide) Copolymers in Aqueous Solutions

Micellization of pH-stimulable poly(2-vinylpyridine)-b-poly(ethylene oxide) copolymers and their complexation with anionic surfactants

The micellization behavior was examined for a series of 3 pH-stimulable poly(2-vinylpyridine)-b-poly(ethylene oxide) (P2VP-b-PEO) copolymers, with a constant composition of 67.5±1.5wt% PEO and increasing molecular weight. The micellar characteristics were determined by dynamic, static and electrophoretic light scattering, fluorescence spectroscopy, as well as by (1)H NMR in the pH range of 2-7 and in the presence or in the absence of the anionic surfactant sodium dodecylsulfate (SDS). In the absence of SDS, two pH regimes were investigated. For the pH range below 5, the micellar characteristics, such as C.M.C., particle size and zeta potential, were determined. For the first time, it could be shown that the micellization range could be extended to low pH values for relatively high copolymer concentrations. Above pH 5, correlations between the molecular characteristics and the aggregation number as well as the hydrodynamic diameter were established. A fair agreement could be demonstrated with the theoretical predictions for star-like micelles having a P2VP core and a PEO corona. Another original aspect of these double hydrophilic copolymers is their complex formation by electrostatic interaction between the protonated P2VP and SDS. At low pH and low copolymer concentrations, where only protonated unimers are present, the SDS induces the micellization at a given neutralization degree (DN). The process of complex formation was analyzed as a function of DN and pH by DLS, fluorescence spectroscopy, zeta potential measurements and by (1)H NMR, this last technique providing information on the mobility of the P2VP/SDS micellar core. A model for the micelle formation mechanism was suggested.

Polyelectrolyte-surfactant complexes formed by poly[3,5-bis(trimethylammoniummethyl)4-hydroxystyrene iodide]-block-poly(ethylene oxide) and sodium dodecyl sulfate in aqueous solutions

Formation of polyelectrolyte-surfactant (PE-S) complexes of poly[3,5-bis(trimethylammoniummethyl)-4-hydroxystyrene iodide]-block-poly(ethylene oxide) (QNPHOS-PEO) and sodium dodecyl sulfate (SDS) in aqueous solution was studied by dynamic and electrophoretic light scattering, small-angle X-ray scattering (SAXS), atomic force microscopy, and fluorometry, using pyrene as a fluorescent probe. SAXS data from the QNPHOS-PEO/SDS solutions were fitted assuming contributions from free copolymer, PE-S aggregates described by a mass fractal model, and densely packed surfactant micelles inside the aggregates. It was found that, unlike other systems of a double hydrophilic block polyelectrolyte and an oppositely charged surfactant, PE-S aggregates of the QNPHOS-PEO/SDS system do not form core-shell particles and the PE-S complex precipitates before reaching the charge equivalence between dodecyl sulfate anions and QNPHOS polycationic blocks, most likely because of conformational rigidity of the QNPHOS blocks, which prevents the system from the corresponding rearrangement.

Interpolymer Complexes Based on the Core/Shell Micelles. Interaction of Polystyrene-block-poly(methacrylic acid) Micelles with Linear Poly(2-vinylpyridine) in 1,4-Dioxane Water Mixtures and in Aqueous Media

The size and structural changes of nanoparticles formed after the addition of poly(2-vinylpyridine), PVP, to block copolymer micelles of polystyrene-block-poly(methacrylic acid), PS-PMA, were studied by light scattering and atomic force microscopy. Due to the strong hydrogen bonding between PVP and PMA segments, complex structures based on the core/shell micelles form in mixed selective solvents. As proven by a combination of light scattering and atomic force microscopy, individual PS-PMA micelles are "glued" together by PVP chains. The dialysis against solvents with a high content of water results in transient increase in polydispersity and turbidity of originally clear solutions. However, the precipitated polymer material dissolves in basic buffers and stable soluble nanoparticles reform in aqueous media. The behavior of their solutions was studied in a broad pH range by light scattering, atomic force microscopy and capillary zone electrophoresis.