In the present study, different series of high-density polyethylene (HDPE) nanocomposites were prepared by melt mixing on a Haake-Buchler Reomixer, containing 2.5 wt % of multiwall carbon nanotubes, pristine and modified montmorillonite, surface-treated anduntreated SiO 2 nanoparticles. From transmission electron micrographs, it was found that beyond a fine dispersion of nanoparticles into HDPE matrix, there are also some aggregates easily discriminated. As a result, there was a decrease in the tensile and impact strength of most of nanocomposites except Young's modulus, which was increased. Storage modulus as recorded from dynamic mechanical analysis was also increased in all nanocomposites, because HDPE becomes stiffer due to the incorporation of nanoparticles. The nucleation behavior of nanoparticles during crystallization was found to have no obvious effect on melting and crystallization temperature of HDPE. However, a small decrease in the heat of fusion in all nanocomposites was evidenced. Gas permeability of HDPE matrix in O 2 , N 2 , and CO 2 was reduced in all nanocomposites compared with neat polymer. Thermal stability of HDPE was also enhanced due to the incorporation of different nanoparticles. From the kinetic analysis of thermal decomposition of HDPE, it was concluded that to describe the thermal degradation of HDPE and the studied nanocomposites, two consecutive mechanisms of nth-order autocatalysis have to be considered.

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Co-based nanostructures ranging from core/shell to hollow nanoparticles were prepared by varying the reaction time and the chemical environment during the thermal decomposition of Co 2 (CO) 8 . Both structural characterization and kinetic model simulation illustrate that the diffusivities of cobalt and oxygen determine the growth ratio and the final morphology of the nanoparticles. Exchange coupling between Co and Co-oxide in core/shell nanoparticles induced a shift of field-cooled hysteresis loops that is proportional to the shell thickness, as verified by numerical studies. The increasing nanocomplexity, when passing from core/shell to hollow particles, also leads to the appearance of hysteresis above 300 K due to an enhancement of the surface anisotropy resulting from the additional spin-disordered surfaces.

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