ABSTRACT:In the present study two series of isotactic polypropylene (iPP)/SiO 2 nanocomposites containing 1, 2.5, 5, 7.5, and 10 wt % SiO 2 nanoparticles were prepared by melt-mixing on a twin-screw corotating extruder. In the first series untreated fumed silica nanoparticles were used, whereas in the second nanoparticles were surface-treated with dimethyldichlorosilane. In both cases, the average size of the primary nanoparticles was 12 nm. Tensile and impact strength were found to increase and to be affected mainly by the type and content of silica nanoparticles. A maximum was observed, corresponding to samples containing 2.5 wt % SiO 2 . These findings are discussed in light of the SEM and TEM observations. By increasing the amount of nanoparticles, large aggregates of fumed silica could be formed, which may explain the reduction of mechanical properties with higher concentrations of SiO 2 . However, it was found that surface-treated nanoparticles produced larger aggregates than did those derived from untreated nanoparticles, despite the increased adhesion of the iPP matrix, as was postulated from yield strength. This behavior negatively affected mechanical properties. In addition, an effort was made to determine if toughening theories, mainly the critical interparticle distance for rubber toughening or composites, also might be applicable in nanocomposites. From DSC measurements it was demonstrated that silica nanoparticles acted as effective nucleating agents, increasing the crystallization rate and the degree of crystallinity of iPP.

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Pt m – Ni n multilayers were grown by e-beam evaporation under ultrahigh vacuum; m and n will depict the number of atomic planes of the corresponding constituents in one modulation period and, in this work, they were varied between 1 and 14. X-ray diffraction and conventional electron microscopy experiments revealed a fcc polycrystalline structure with excellent modulation. Magneto-optic properties, studied at room temperature between 1.5 and 5.2 eV, were found to depend strongly on both m and n. Perpendicular anisotropy was exhibited for samples with thin Ni layers and, unexpectedly, for thicker Ni layers when Pt layers became considerably thin (m∼2). Comparison of the magneto-optic features of two similar samples grown on glass and polyimide revealed that the choice between glass and polyimide does not affect magneto-optic properties.

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