A simple method was used to assemble single-walled carbon nanotubes into indefinitely long ribbons and fibers. The processing consists of dispersing the nanotubes in surfactant solutions, recondensing the nanotubes in the flow of a polymer 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.

We report on the formation of colloidal complexes resulting from the electrostatic self-assembly of polyelectrolyte−neutral diblock copolymers and oppositely charged surfactant. The copolymers investigated are asymmetric and characterized by a large neutral block. Using light, neutron, and X-ray scattering experiments, we have shown that the colloidal complexes exhibit a core−shell microstructure. The core is described as a dense microphase of micelles connected by the polyelectrolyte blocks, whereas the shell is a diffuse brush made from the neutral chains. For all copolymer/surfactant systems, we show the existence of a critical charge ratio Z C (∼1) above which the formation of hierarchical structures takes place. Copolymers of different molecular weight and polyelectrolyte blocks have been studied in order to assess the analogy with another type of core−shell aggregates, the polymeric micelles made from amphiphilic copolymers. The present results indicate that the radius of the core depends essentially on the degree of polymerization of the polyelectrolyte block and not on that of the neutral chain. On the other hand, the size of the overall colloid increases with increasing molecular weights of the copolymers. Taking advantage of the resolution of X-ray scattering, we have also shown that the micelles in the core of the aggregates are structurally disordered.

Percolation is a statistical concept that describes the formation of an infinite cluster of connected particles or pathways. Lowering the percolation threshold is a critical issue to achieve light and low-cost conductive composites made of an insulating matrix loaded with conductive particles. This has interest for applications where charge dissipation and electrical conductivity are sought in films, coatings, paints, or composite materials. One route to decreasing the loading required for percolation is to use rod-like particles. Theoretical predictions indicate that this may also be achieved by altering the interaction potential between the particles. Although percolation may not always respond monotonically to interactions, the use of adhesive rods can be expected to be an ideal combination. By using a system made of carbon nanotubes in an aqueous surfactant solution, we find that very small attraction can markedly lower the percolation threshold. The strength of this effect can thereby have direct technological interest and explain the large variability of experimental results in the literature dealing with the electrical behavior of composites loaded with conducting rods.