By the use of small angle neutron scattering, the chain conformation in a polymer nanocomposite was studied as a function of the nanoparticle fraction for two different molecular weights. A repulsive system was realized in mixing poly(ethylene-propylene) and hydrophobically modified silica. All nanocomposite SANS data exhibit a pronounced scattering peak at intermediate momentum transfers, which is closely connected with the particle structure. Even under contrast matching conditions, the hydrophobic surface layer of the nanoparticles was found to contribute significantly to the scattering signal. In particular, in the short chain matrix the peak origin is exclusively related to direct particle scattering. In the long chain matrix, an additional peak contribution is present. Possible origins include void correlation scattering or polymer correlation scattering. We show unambiguously that the conformation of short chains with a molecular weight of 3000 g/mol is not visibly disturbed by the presence of the nanoparticles. In contrast to that a polymer matrix with 50 000 g/mol chains is affected by the particle presence. The chain radius of gyration R g decreases.

The magnetic 2D to 3D crossover behavior of well-ordered arrays of monodomain γ-Fe(2)O(3) spherical nanoparticles with different thicknesses has been investigated by magnetometry and Monte Carlo (MC) simulations. Using the structural information of the arrays obtained from grazing incidence small-angle X-ray scattering and scanning electron microscopy together with the experimentally determined values for the saturation magnetization and magnetic anisotropy of the nanoparticles, we show that MC simulations can reproduce the thickness-dependent magnetic behavior. The magnetic dipolar particle interactions induce a ferromagnetic coupling that increases in strength with decreasing thickness of the array. The 2D to 3D transition in the magnetic properties is mainly driven by a change in the orientation of the magnetic vortex states with increasing thickness, becoming more isotropic as the thickness of the array increases. Magnetic anisotropy prevents long-range ferromagnetic order from being established at low temperature and the nanoparticle magnetic moments instead freeze along directions defined by the distribution of easy magnetization directions.

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Thermoresponsive hydrogels were prepared upon radiation-induced copolymerization of aqueous micellar solutions containing N-isopropylacrylamide (NiPAAm) and a cationic surfactant monomer (surfmer), and of microemulsions containing NiPAAm, surfmer, and styrene. Three surfmer compounds were used: (11-(acryloyloxy)undecyl)trimethylammonium bromide (AUTMAB), (11-(methacryloyloxy)undecyl)trimethylammonium bromide (MUTMAB), and (2-(methacryloyloxy)ethyl)dodecyldimethylammonium bromide (MEDDAB). Comonomer solutions were studied on their phase behavior and structure using small-angle neutron scattering (SANS). The presence of surfmers increased the solubility of NiPAAm in the aqueous phase. SANS studies indicate that the surfmers form spherical micelles, which in the presence of styrene are increased and in the presence of NiPAAm are decreased in size. Styrene is incorporated in the core, and NiPAAm is incorporated in the shell of the micelles. If styrene and NiPAAm are present, the effects of both compensate each other, the micelle size remains unchanged, and only small amounts of styrene are solubilized. Evaluation of scattering curves indicated remarkable changes in headgroup dissociation of surfmers in the presence of NiPAAm in the micellar solutions. If exposed to (60)Co-gamma irradiation (dose: 80 kGy), stable, transparent, and thermoresponsive hydrogels were directly obtained. The lower critical solution temperature (LCST) of gels containing surfmer in low concentration was higher than that for pure NiPAAm gels, whereas in gels with high surfmer concentration it was lower. The lowest LCST was observed if MEDDAB was present in the gel. 1 % (w/w) was already sufficient to lower the LCST from 33.2 to 28.5 degrees C. Gels with low surfmer concentration (< or = 1 wt %) exhibited a strong, rapid swelling in water at 20 degrees C and a rapid and reversible shrinking at 50 degrees C. For a gel containing 1% AUTMAB, the swelling ratio was 2.4 times higher (MUTMAB, 2.8; MEDDAB, 1.5) than that for a pure NiPAAm gel. Copolymer gels containing more than 1 wt % surfmer exhibited a strong and rapid swelling below and above the LCST, because the copolymerized ionic surfmer induced an osmotic pressure in the gel. The effects of a variation of NiPAAm and surfmer concentration were studied, and the origins of the thermoresponsive properties are discussed.

We report a new "grafting to" technique for the functionalization of silica particles with anionically produced polymers. It is based on a two-step procedure. In the first step the silica nanoparticles were modified with multifunctional chlorosilanes. This procedure allows replacing the original Si-OH surface groups by Si-Cl groups. In the second step the anionically synthesized polymers were linked to the Si-Cl functionalized nanoparticle surface. Both the chlorosilane functionalization of the nanoparticles and the subsequent reaction with living polymer can be carried out without irreversible particle aggregation. This was proved by examining the reaction products with static and dynamic light scattering as well as small-angle X-ray scattering. The polymer linking event is accompanied by termination reactions, most likely due to residual Si-OH groups. Therefore, the raw products were purified by a simple fractionation procedure. The examination of the products by size exclusion chromatography showed that this procedure allowed removing the free polymer quantitatively. The new anionic based method offers the possibility for grafting densities up to 1 chain per nm 2 of particle surface, which is significantly higher than reported in the past for other "grafting to" approaches. The now obtained grafting densities are similar to the ones reported for "grafting from" techniques which are mainly based on controlled radical polymerization. Our new approach offers the possibility to obtain hybrid materials containing polymers which are not accessible via controlled radical techniques like polydienes. In addition, the new technique allows grafting polymers having molecular weights up to 500 000 g/mol and still narrow molecular weight distributions.