The phase behavior of a low molecular weight (M W = 4000) diblock copolymer of polystyrene and poly(ethylene oxide), PS−PEO, in the bulk as well in aqueous, D2O, solutions has been studied using small-angle neutron-scattering, dynamic and static light-scattering, and rheological methods. At low temperature the pure block copolymer forms a lamellar mesophase driven by the crystallization of PEO. The melting point of PEO, T ≈ 64 °C, is correspondingly accompanied by an order-to-disorder transition. The melt is typified by single-exponential depolarized correlation functions in the dynamic light-scattering spectra, observed in the temperature range 60 to 100 °C. Neutron scattering fails to show concentration fluctuations in the amorphous, disordered phase due to lack of contrast. In aqueous solutions up to roughly 20% polymer concentration, PS−PEO self-associates into spherical micelles with a core size of R c ≈ 56 Å and an interaction radius R hs ≈ 115 Å, corresponding to an aggregation number of 470. The hydrodynamic radius R h = 140 Å obtained from dynamic light scattering is close to but somewhat larger than the interaction radius, as expected. Extended clusters, displaying a small but significant anisotropy, form at above C = 10% and coexist with the single spherical micelles. These clusters may be due to association of spherical micelles or micelles of different form attributed to residual aggregates of PS moities.

Micellization in water of two homologous series of AB-type diblock copolymers, composed of polystyrene (PS) as the A block and poly(ethy1ene oxide) (PEO) as the B block, were investigated by small-angle X-ray scattering (SAXS) and dynamic light scattering (DLS). The copolymers have molecular weights &, in the range 2000-34800, and have in a given series, the same number of repeating units of the PS block, (Nps = 10 and 38), and a variable number of repeating units of the PEO block (NpEo values in the range 23-704).In order to avoid secondary association of micelles, a dialysis technique was used to prepare the micellar systems, in the case of copolymers having high I @ , , values of the PS block. The experimental micelle properties such as the core radius R, and the aggregation number N of non-equilibrium structures, so called "frozen micelles", obtained by dialysis, were found to be independent of the copolymer characteristics. However, for equilibrium structures, obtained by direct solubilization of the copolymers (Nps = 10) in water, R, and N were found to decrease with increasing NpEo for the homologous series.

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A small-angle X-ray scattering (SAXS) study of micelles formed by a symmetric block copolymer consisting of poly(styrene) and poly(ethylene oxide) (molecular weight of each block:  1000 g/mol; concentration up to 15.4 wt %) is given. The contrast of the micelles toward water was changed by adding glycerol to the solution. The analysis of the SAXS data shows that the addition of glycerol does not change the structure of the micelles. With the aid of contrast variation, SAXS allows determination of the following integral parameters:  (i) the mean electron density of the particle ρ together with the particle volume V p, (ii) the radius of gyration at infinite contrast R g, ∞ together with the inhomogeneity parameter α, and (ii) the volume V c related to the shape of the particles as well as parameters characterizing the internal density fluctuation of the particles. Furthermore the correlation length l c has been determined as a function of concentration and contrast. A comparison of these parameters and of the scattering intensities at various contrast with concentric models of the radial electron density shows the following:  The micelles have an overall spherical shape and a narrow size distribution (weight-average aggregation number = 400; standard deviation of the size distribution 10.9%). The unpolar component poly(styrene) together with a fraction of the polar poly(ethylene) blocks is located in the core.

a b s t r a c t Keywords: Palygorskite TiO 2 Photocatalysis Inorganic-inorganic nanocomposites Orange G pollutantThis study deals with the synthesis of TiO 2 supported Moroccan palygorskite fibers and their use as photocatalyst for the removal of Orange G pollutant from wastewater. The TiO 2 -palygorskite nanocomposite synthesis was accomplished according to a colloidal route involving a cationic surfactant as template (hexadecyltrimethylammonium bromide) assuring hence organophilic environment for the formation of TiO 2 nanoparticles. The clay minerals samples were characterized before and after functionalization with TiO 2 . Anatase crystallizes above ca. 450°C and remarkably remains stable up to 900°C. In contrast, pure TiO 2 xerogel obtained from titanium tetraisopropoxide (TTIP) showed before calcination a nanocrystalline structure of anatase. By increasing the temperature, anatase readily transforms into rutile beyond 600°C. The remarkable stability at high temperature of anatase particles immobilized onto palygorskite microfibers was due to the hindrance of particles growth by sintering. Homogeneous monodisperse distribution of anatase particles with an average size of 8 nm was found by TEM and XRD onto palygorskite fibers. This anatase particle size remains below the nucleus critical size (ca. 11 nm) required for anatase-rutile transition. The TiO 2 supported palygorskite sample annealed in air at 600°C for 1 h exhibits the highest photocatalytic activity towards the degradation of Orange G compared to nanocomposite samples prepared under different conditions as well as pure TiO 2 powders obtained from the xerogel route or commercially available as Degussa P25.

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