The micellization of the triblock copolymer Pluronic P85 (poly(oxyethylene)27/poly(oxypropylene)39/poly(oxyethylene)27) in aqueous solution was followed vs temperature and addition of aliphatic alcohols, using the spin probe technique. Different types of probes properly chosen (spin-labeled (SL) poly(oxyethylene(4))nonylphenol, SL-Pluronic L62, TEMPO-laurate, TEMPO-hexanoate, CAT 4, CAT 8, CAT 11, CAT 16, and 5-, 7-, 10-, and 12-doxylstearic acids) provided information about the micellar structure (polarity, viscosity, and order degree) at different radial locations. Micellization was found to be low at room temperature, even for 10% aqueous solutions, but strongly increasing with temperature increase to about 323 K. Hydration of the poly(oxyethylene) (PEO) chains in the shell was found to diminish toward the interior and with increasing temperature. At an intermediate region of the shell, a hydration number ([H2O]/EO unit) close to 3 was found at 293 K, which decreased to ∼1 at 323 K. No hydration was found in a region corresponding to 4−6 EO units from the core. At the PPO/PEO interface, a further decrease in polarity occurred in the 323−373 K temperature range, probably due to an extension of the hydrophobic core with increasing temperature, with prevalence of the nonpolar conformations of the PPO and PEO chains. At 323 K, the order degree of the PEO chains decreased rapidly toward the interior of the shell. Addition of medium chain aliphatic alcohols to the aqueous solution of the polymer substantially enhanced micellization at room temperature. The effect increased with the alcohol chain lenght in the C4−C6 series. The addition of alcohols (C5, C6) was found to have similar effects with temperature increase, i.e., to promote micellization and to reduce the hydration and the order degree in the shell. In both cases the effects are due to an increased hydrophobe character of the core.

A series of Au nanoparticles functionalised with nitroxide spin labels has been prepared and studied by EPR spectroscopy. Samples with low coverage of the spin label were used to investigate the dynamics of the surface-attached labels at different distances from the Au surface. The rotational correlation times of spin labels vary from 10(-10) s to more than 3 x 10(-9) s, depending on the chain length of the label and the surrounding ligand. The samples with higher coverage of the spin label show an increasing contribution of the exchange interaction between nitroxides adsorbed in a close proximity to each other on the same nanoparticle. Quantitative analysis of the EPR spectra of these samples suggests the presence of non-equivalent binding sites on the surface of Au nanoparticles. Additionally, EPR signals of isolated radical pairs were observed at intermediate coverage.

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The rheological properties of wormlike micellar solutions formed by the pseudo-ternary system sodium dodecyl sulfate (SDS)−Al(NO3)3−H2O have been studied at a fixed molar ratio Al(NO3)3:SDS = 5.92:1 as a function of surfactant concentration. The linear data show that solutions behave as a Maxwell fluid and there are two well-defined domains characterized by scaling laws for surfactant concentration, with a maximum in the viscosity−surfactant concentration curve. Prior to the maximum, the system consists of linear micelles, and η0 (zero-shear rate viscosity) and τR (relaxation time) are found to scale with surfactant concentration with exponents higher than those predicted by the theory of Cates. The results in the second domain are not reflected by the dynamic behavior of entangled wormlike micelles, and they are interpreted in terms of formation of connected micelles. The nonlinear rheology is governed by the shear banding effect occurring for viscous entangled wormlike micellar solutions and branched micelles, and the properties identified by reduced stress σp/G 0 and the Weissenberg number, γ̇cτR, are compared to the values predicted on the basis of the theoretical model.