Effects of self-generated electric and magnetic fields in laser-generated fast electron propagation in solid materials: Electric inhibition and beam pinching

We present some experimental results which demonstrate the presence of electric inhibition in the propagation of relativistic electrons generated by intense laser pulses, depending on target conductivity. The use of transparent targets and shadowgraphic techniques has made it possible to evidence electron jets moving at the speed of light, an indication of the presence of self-generated strong magnetic fields

Fast electron transport and heating in solid-density matter

Two experiments have been performed to investigate heating by high-intensity laser-generated electrons, in the context of studies of the fast ignitor approach to inertial confinement fusion (ICF). A new spectrometer and layered targets have been used to detect Kα emission from aluminum heated by a fast electron beam. Results show that a temperature of about 40 eV is reached in solid density aluminum up to a depth of about 100 μm

Polypropylene/clay nanocomposites revisited

This thesis is devoted to the optimization of polypropylene (PP)/clay nanocomposites preparation by trying to resolve or find alternatives to the actual limitations of producing PP/clay nanocomposites which restrain their industrial development. A large part of this work is focused on the study and optimization of functionalized polypropylenes as compatibilizers and an optimized PP-graft-maleic anhydride (PP-g-MA), having significantly higher graft content than classic PP-g-MAs, was selected. The synthesis and characterization of carboxylate clays is fully investigated in view to examine alternatives to alkylammonium clays for the preparation of PP/clay nanocomposites. Carboxylate clays are more thermally stable than a classic alkylammonium clay and do not degrade at extrusion temperature. The elaboration of PP/(organo)clay nanocomposites is also investigated through a water-assisted extrusion process. The use of water injection during the production of nanocomposites showed a remarkable effect in increasing the clay dispersion. At last, the traditional elaboration of PP/clay nanocomposites is revisited by using the knowledge developed in this work. PP/clay nanocomposites were processed through a one-step water-assisted extrusion method using optimized PP-g-MA compatibilizers, carboxylate salts and native clay.(CHIM 3) -- UCL, 201

Polypropylene/clay nanocomposites: An innovative one-pot process

This work discloses a novel one-pot preparation method of polypropylene (PP)/clay nanocomposites with high degree of clay delamination and improved thermal, mechanical and rheological properties. The in situ simultaneous synthesis of carboxylate clay from native clay and ionomer of PP-graft maleic anhydride (PP-g-MA) through trihydrate sodium acetate addition, combined with water injection in the extrusion process, appears to be a valuable alternative to the use of organoclay for producing PP/PP-g-MA/clay nanocomposites. The influence of PP-g-MA graft content, and of its ionomer form, onto the clay dispersion has been especially investigated. PP-g-MA of low graft content is compared to a home-made highly grafted PP-g-MA synthesized in the presence of N-bromosuccinimide (NBS). The nanocomposites prepared by combining the use of NBS-mediated PP-g-MA, trihydrate sodium acetate and water injection exhibit the highest clay dispersion. Thermal, rheological, and mechanical properties of the nanocomposites have been measured

Tuning the functionalization chemistry of polypropylene for polypropylene/clay nanocomposites

New polypropylene (PP)-graft-maleic anhydride (PP-g-MA) samples have been successfully synthesized by adding N-bromosuccinimide (NBS) during the reactive extrusion process. These NBS-mediated PP-g-MAs possess higher graft content than classic PP-g-MAs (i.e. without NBS) while they keep acceptable molar masses. NBS-mediated PP-g-MAs were used as matrices in model PP-g-MA/organoclay nanocomposites and compared with commercial and home-made classic PP-g-MAs in order to evaluate their ability to disperse the clay. Significantly better degrees of clay delamination and dispersion were reached using NBS-mediated PP-g-MAs than with classic PP-g-MAs. As expected, PP-g-MAs having high graft content showed the best clay dispersion. Within the examined range of molar masses, the PP-g-MA molar mass had no influence on the clay dispersion. However PP-g-MAs exhibiting important reduction of crystallinity lead to poor clay dispersion whatever the graft content. The PP-g-MA/organoclay nanocomposite prepared using the selected "optimized" NBS-mediated PP-g-MA exhibited the best improvement of thermal properties and one of the best clay dispersions. PP/PP-g-MA blends were prepared to evaluate the miscibility between PP and selected PP-g-MAs. No problem of miscibility between the selected NBS-mediated PP-g-MA and PP was noticed. Finally the PP/organoclay prepared using the selected NBS-mediated PP-g-MA as compatibilizer showed much better clay dispersion and thermal stability than the one prepared with the corresponding classic PP-g-MA, thus establishing the interest to use such new NBS-mediated PP-g-MAs as compatibilizers. © 2011 Elsevier Ltd. All rights reserved

Carboxylate clays: A model study for polypropylene/clay nanocomposites

Sodium-montmorillonite was intercalated by carboxylate salts to prepare carboxylate clays. The intercalation of sodium acetate doubles the clay basal spacing and no degradation of the carboxylate clay is noticed in the extrusion temperature range. These carboxylate clays were used to synthesize polypropylene-graft-maleic anhydride (PP-g-MA)/clay nanocomposites. Nanocomposites were also produced by a one-pot process using in situ prepared carboxylate clay. The carboxylate salts within the clay layers partially neutralize the maleic anhydride groups of the PP-g-MA matrix, in situ during the melt compounding. The ionic groups of the partially neutralized polymer offer favourable interactions with the clay, hence reinforcing the interfacial bond between the polymer and the clay and improving the composite properties. The use of carboxylate clay clearly improves the clay dispersion into the PP-g-MA matrix and improves the nanocomposite's thermal and rheological properties

An original combined method for electrical conductivity measurement of polymer composites under extensional deformation

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High Impact Polystyrene/CNT nanocomposites: Application of volume segregation strategy and behavior under extensional deformation

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High Impact Polystyrene/CNT nanocomposites: Application of volume segregation strategy and behavior under extensional deformation

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A model for the electrical conductivity variation of molten polymer filled with carbon nanotubes under extensional deformation

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