Dispersions and fibers of carbon nanotubes
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Dispersions and fibers of carbon nanotubes
Brigitte Vigolo, Alain Pénicaud, Claude Coulon, Cédric Sauder1, René Pailler1, Catherine Journet2, Patrick Bernier2, Philippe Poulin Centre de Recherche Paul Pascal / CNRS, Université Bordeaux I, Avenue Schweitzer, 33600 Pessac, France 1-LCTS, Allée de la Boëtie, 33600 Pessac, France 2-GDPC, Université de Montpellier II, 34095 Montpellier, France ABSTRACT We study the phase behavior of single walled carbon nanotubes in aqueous solutions of surfactant molecules or amphiphilic polymers. Homogeneous dispersions can be obtained by using sodium dodecyl sulfate (SDS) in a well-defined concentration range. In contrast, polyvinyl alcohol (PVA) is not efficient at stabilizing the tubes. Carbon nanotubes stick with each other when PVA is added to homogeneous dispersions initially stabilized by SDS. This behavior is the basis of a simple method that we developed to assemble single walled carbon nanotubes into indefinitely long ribbons and fibers. The processing consists of dispersing the nanotubes in SDS solutions, re-condensing the nanotubes in the flow of a PVA solution to form a nanotube mesh, and then collating this mesh to a nanotube fiber. Flow induced alignment may lead to a preferential orientation of the nanotubes in the mesh that has the form of a ribbon. Unlike classical carbon fibers, the nanotube fibers can be strongly bent without breaking. Their obtained elastic modulus is 10 times higher than the modulus of high-quality bucky paper. INTRODUCTION Single wall carbon nanotubes (SWNTs) are very promising materials because of their exceptional mechanical and electro-mechanical properties [1-7]. Unfortunately, despite their intrinsic rigidity and high anisotropy, most of the currently available macroscopic forms of SWNTs are isotropic and rather fragile. These forms mainly consist of raw powder-like materials originating from the synthesis [8,9], suspensions in solvents [10], and thin mat, known as bucky paper, obtained by drying SWNTs suspensions [11]. Processing nanotubes on macroscopic scales to obtain materials of more practical use is a major challenge. Recent progresses have shown the possibility to make films of aligned nanotubes by using high magnetic fields [12] or fibers of aligned nanotubes by using an electrophoretic process [13]. In both cases, the nanotubes are initially dispersed in liquid media. Dispersing nanotubes is also widely used to make filtrations and purifications of raw materials [11]. To be dispersed in a given medium carbon nanotubes have to be either chemically modified [10] or coated by adsorbed amphiphilic molecules. The last method is straightforward and is classically employed to disperse SWNT in water with the help of commercially available surfactant molecules. The A12.1.1
phase behavior of these suspensions is of critical importance, as it will determine the structure and the properties of the materials issued from the dispersions. In this work, we present a detailed study of the phase behavior of SWNT suspensions in aqueous solutions o
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