Use of functionalized nanosilica to improve thermo-mechanical properties of epoxy adhesive joint bonding aluminium substrates.

The present work is concerned with the improvement of thermal properties and mechanical strength of adhesive joints consisting of an epoxy adhesive layer bonding aluminium substrates by grafted nanosilica. Epoxy resin/silica nanocomposites were prepared by using functionalized silica. Silica was functionalized by amine group (SiO2-NH2). It was identified by Raman and Fourier Transform Infrared (FTIR). Effects of silica on viscoelastic properties for epoxy resin and its assemblies with aluminium substrates were studied by Dynamical Mechanical Analysis (DMA). Particles distribution was characterized by Scanning Electron Microscope (SEM). Our experimental results showed that functionalized silica presents a better distribution in the matrix than the pure silica. Our results also showed that grafting of functionalized silica improves the glass transition temperature (Tg) and the ultimate strength of aluminium/epoxy/aluminium assembly.

The beta-spherulite morphology of isotactic polypropylene investigated by Raman spectroscopy.

Raman spectroscopy is used to investigate the alpha- and beta-crystalline polymorphs of isotactic polypropylene. Raman spectra of the polymorphs show some minor differences, in particular the wavenumber shifting of certain scattering bands, which reflect the environment of an isolated macromolecular chain within the packing unit cell of the different crystal forms. For example, the shifting of the 842 cm(-1) scattering band, which is the most susceptible band to cause intermolecular interactions, is used to generate a structural map of one beta-spherulite among alpha-spherulites with a well-defined resolution. Anisotropy of the crystalline phase orientation within a beta-spherulite is also investigated by performing polarized Raman spectroscopy measurements. Differences in the polarized spectra are then finely exploited to map the radial lamellae orientation distribution within one beta-spherulite.

Accurate determination of the anisotropy factors and the phase differences of Raman polarizabilities in some uniaxial crystals: the case of lithium niobate.

The present study highlights self-consistently helpful improvements dedicated to overcoming the difficulty resulting from the fitting procedure of integrated Raman intensities recorded according to the rotation crystal method described earlier. To this end, the anisotropy factors of Raman polarizabilities and the corresponding relative phases are determined within the framework of the exact mathematical derivation of the phase factors. These are the relevant parameters of the Raman efficiency relations which are numerically difficult to obtain from the fitting of the integrated areas. The present theoretical approach is then applied to the modes of the A(1) and Ey symmetry species of the lithium niobate (LN) crystal point group. All the expressions of the Raman absolute intensities of the A(1) and Ey irreducible representations initially imply three parameters to be determined from the fitting computations. However, from the derived analytical expressions of the phase differences, the number of parameters involved in the fitting procedure is reduced from 3 to 2, thus improving the statistics of the numerical treatment.