Radial collapse of carbon nanotubes for conductivity optimized polymer composites

The optimization of the electronic conduction of carbon nanotube polymer composites is studied by tuning the radial geometry of the carbon nanotubes in a compression cycle. We have investigated the structural evolution of multi-walled carbon nanotubes in a polyamide matrix as a function of applied high pressure. Combining high resolution electron microscopy and small angle neutron scattering experiments, we conclude that the nanotube radial cross-section is irreversibly deformed following applied pressures up to 5 GPa. Studying highly percolated composites we observe that the sample resistivity drastically decreases with pressure up to about 2 GPa with no further change up to the maximum 5 GPa applied pressure. An important hysteresis is observed upon decompression which leads to an enhanced electrical conductivity of the composite in all the studied compression cycles with maximum pressures ranging from 1 to 5 GPa. Modelling the radial collapse of single-walled carbon nanotubes shows that the modified radial geometry can considerably improve the electronic transport properties in contacted carbon nanotube junctions. Our results open opportunities for engineering nanotube composites by controlling the radial collapse

Eponges composites cellulose/NTC pour la dépollution des hydrocarbures

National audienc

Elaboration and characterization of materials obtained by pressing of vermiculite without binder addition

International audienc

In situ Evolution of the porous Structure of expanded graphite under uniaxial pressure

International audienc

Elaboration and characterization of materials obtained by pressing of vermiculite without binder addition

International audienceVermiculite materials were obtained by uniaxial pressing of potassic vermiculite powders obtained by sonication without any binder addition. The vermiculite powders, made of aggregates of particles with nanometric thick-ness and micrometric in plane dimension, were pressed in the range 17.7–80 MPa at room temperature and 200 °C, and further annealed in the range 400–800 °C. Pressing powders at 200 °C instead of 25 °C allowed the slight increase of the density of the formed materials (from 1.9 to 2 g·cm −3) due to the desorption of the water molecules from the interaggregate and interparticle spaces, allowing a higher densification. The density was also increased by tailoring the particle size distribution. The pressed materials were formed of oriented arrangement of vermiculite aggregates. The porous structure, characterized by mercury porosimetry, scanning electron microscopy, and small angle X-ray scattering, was modelled by oriented oblate spheroidal pores formed in the voids between the stacked aggregates organized in a structure possessing a cylindrical symmetry. The porous structure was found to vary with the pressure and the annealing temperature

Socio-economic factors influencing small-scale farmers' market participation : case of rice producers in Dano

This paper explores the key factors influencing market participation decisions among smallholder lowland rice growers. Data were collected through purposive sampling technique. A total of 127 rice growers, from 16 lowlands (developed and traditional lowlands), was selected. Descriptive statistics and the probit regression model were used to analyse the data. The statistical analysis revealed significant differences in yields between developed and traditional lowlands rice plots ("lowland development effect"). The regression results showed that farmers' behaviours were not gender neutral; male producers were more likely to take part in the market as compared to their female counterparts, implying a "gender effect". With respect to the effect of membership in farmers' organization, the results indicate that farmers' involvement in an organization, was in general negatively associated to their market participation decisions. However, farmers from lowlands with functional rice producers' organizations were more likely to sell their products in the market. Interestingly, this study also highlighted that lowland rice producers' ability to generate a marketable surplus (at least 20 kg/person/year) positively influence their market participation decision. As hypothesized, the results revealed that farmers who have access to potential buyers of the output (secured market outlets) were less likely to produce rice for self-consumption