Correlation of properties with preferred orientation in coagulated and stretch-aligned single-wall carbon nanotubes

We report structure-property correlations in single wall carbon nanotube (SWNT) fibers, among electrical, thermal and chemical parameters with respect to stretch-induced preferential SWNT alignment along the fiber axis. Purified HiPco tubes are dispersed with the aid of an anionic surfactant and coagulated in the co-flowing stream of an adsorbing polymer. The fibers are then dried, rewetted under tensile load and redried to improve the alignment. Complete removal of the polymer was assured by annealing in hydrogen at 1000oC. The degree of alignment was determined by x-ray scattering from individual fibers using a 2-dimensional detector. The half width at half maximum (HWHM) describing the axially symmetric distribution of SWNT axes decreases linearly from 27.5o in the initial extruded fiber to 14.5o after stretching by 80%. The electrical resistivity ρ at 300 K decreases overall by a factor ~4 with stretching, for both as-spun composite and polymer-free annealed fibers. However, the temperature dependence ρ(T) is markedly different for the two, implying different electron transport mechanisms with and without the polymer. Thermal conductivity also improves with increasing alignment, while the absolute values are limited by the disordered network of finite length tubes and bundles. Comparisons are made with results from similar fibers spun from oleum, and with magnetically aligned buckypapers

Etude de suspensions et de fibres de nanotubes de carbone

Ce travail de thèse concerne l'étude de dispersions et de fibres de nanotubes de carbone. Nous nous sommes intéressés à l'influence de la structure des nanotubes et de la nature des dispersants sur la topologie des diagrammes de phases des suspensions. Nous montrons par ailleurs que les dimensions des nanotubes peuvent être caractérisées en suspension par diffusion dynamique dépolarisée de la lumière. Le deuxième aspect de ce travail concerne l'étude et l'optimisation des propriétés mécaniques, électriques et électromécaniques de fibres de nanotubes de carbone formulées grâce aux acquis de la partie précédente. Nous montrons que les fibres de nanotubes sont des systèmes prometteurs pour la réalisation de matériaux haute ténacité, de capteurs ou encore d'actionneurs électromécaniques.This thesis deals with the study of carbon nanotube suspensions and fibers. We have studied the influence of the nanotube structure and dispersants on the topology of phase diagrams of suspensions. In addition, we show that carbon nanotube dimensions can be characterized in suspension by depolarized dynamic light scattering. The second part of this work deals with the study and the optimization of mechanical, electrical and electromechanical properties of carbon nanotube fibers. We show that carbon nanotube fibers are particularly promising systems for the realization of high toughness materials, sensors and electromechanical actuators

Etude de suspensions et de fibres de nanatubes de carbone

Ce travail de thèse concerne l'étude de dispersions et de fibres de nanotubes de carbone. Nous nous sommes intéressés à l'influence de la structure des nanotubes et de la nature des dispersants sur la topologie des diagrammes de phases des suspensions. Nous montrons par ailleurs que les dimensions des nanotubes peuvent être caractérisées en suspension par diffusion dynamique dépolarisée de la lumière. Le deuxième aspect de ce travail concerne l'étude et l'optimisation des propriétés mécaniques, électriques et électromécaniques de fibres de nanotubes de carbone formulées grâce aux acquis de la partie précédente. Nous montrons que les fibres de nanotubes sont des systèmes prometteurs pour la réalisation de matériaux haute ténacité, de capteurs ou encore d'actionneurs électromécaniques.BORDEAUX1-BU Sciences-Talence (335222101) / SudocSudocFranceF

An experimental and simulation study on the self-assembly of colloidal cubes in external electric fields

When a suspension of colloidal particles is placed in an oscillating electric field, the contrast in dielectric constant between the particles and the solvent induces a dipole moment in each of the colloidal particles. The resulting dipole-dipole interactions can strongly influence the phase behavior of the system. We investigate the phase behavior of cube-shaped colloidal particles in electric fields, using both experiments and Monte Carlo simulations. In addition to a string fluid phase and a body centered tetragonal (BCT) crystal phase, we observe a columnar phase consisting of hexagonally ordered strings of rotationally disordered cubes. By simulating the system for a range of pressures and electric field strengths, we map out the phase diagram, and compare the results to the experimentally observed phases. Additionally, we estimate the accuracy of a point-dipole approximation on the alignment of cubes in string-like clusters. This journal i

An experimental and simulation study on the self-assembly of colloidal cubes in external electric fields

When a suspension of colloidal particles is placed in an oscillating electric field, the contrast in dielectric constant between the particles and the solvent induces a dipole moment in each of the colloidal particles. The resulting dipole-dipole interactions can strongly influence the phase behavior of the system. We investigate the phase behavior of cube-shaped colloidal particles in electric fields, using both experiments and Monte Carlo simulations. In addition to a string fluid phase and a body centered tetragonal (BCT) crystal phase, we observe a columnar phase consisting of hexagonally ordered strings of rotationally disordered cubes. By simulating the system for a range of pressures and electric field strengths, we map out the phase diagram, and compare the results to the experimentally observed phases. Additionally, we estimate the accuracy of a point-dipole approximation on the alignment of cubes in string-like clusters. This journal i