Carbon nanotubes are widely used as nanocharges in polymer matrix composites for improvingmechanical or electrical properties. Nanocomposites can be prepared either in the solid or in theliquid state, and in the latter case by mixing nanotubes with either melted polymers or polymersolutions. To date, controlled dispersion of CNTs in a solution or a composite remains achallenge, due to the strong van der Waals binding energies associated with the CNTaggregates. Dispersion of nanotubes with high yields, as well as high amounts of individualnanotubes, can be prepared in water with the help of surfactants. However, when using suchsuspensions as precursors for nanocomposites, the final materials will contain some surfactantswhich will influence their physical properties. On the other hand, dispersing nanotubes directlyin polymer solutions without using surfactants leads to low yields and poor individualization.In this work, we propose an alternative and simple way to disperse single-walled carbonnanotubes (SWNT) in aqueous solutions of two hydrosoluble polymers, polyvinyl alcohol (PVA)and polyvinyl pyrrolidone (PVP). We measure the yield using visible-NIR absorptionspectroscopy, and we probe both the chemical environment of the nanotubes and theeffectiveness of individualization from coupled Raman/Photoluminescence studies. First, we mixaqueous suspensions of SWNT stabilized with bile salts (BS) with aqueous solutions of PVA,and we evidence a direct exchange of BS molecules and PVA chains at the surface of SWNT.By contrast, no exchange is observed with PVP. Second, we show that a simple dialysisprocess leads to the preparation of aqueous suspensions of SWNT covered by PVA or PVPwith high yields and an effective individualization of the nanotubes. This simple method opens anew way for preparing surfactant-free polymer matrix composites with high concentrations ofindividual SWNT.

Nanotube-based patterns and films have exciting potential applications in electronics and opto-electronics. One of the key issues to optimize the electrical and optical properties of nanotube arrays is the control of their orientation. So far, orientation of nanotubes in thin films was achieved i) directly during CVD growth [1], ii) using liquid dispersions: by electrophoresis [Herman], in an hydrodynamic flow [Poulin,Li], in the field of an host liquid crystal [Ould-Moussa], by formation of a liquid crystal in concentrated suspensions [Zamora-nem], or iii) by stretching composites [Zamora-pol]. However, versatile and industry-compatible methods are still needed, and inkjet printing appears to be a good candidate. Recently, Denneulin et reported an heterogeneous orientation of SWNT in inket printed lines, with a preferential orientation parallel to the lines at the edges and perpendicular in the sub-surface [Denneulin]. On the other hand, Beyer et al reported an homogeneous alignment parallel to the lines for inkjet printed SWNT, and assigned it to the formation of a nematic phase for special printing rates [Beyer]. Here, we present a coupled Raman/SEM study of the alignment of SWNT during inkjet printing of aqueous suspensions as a function of temperature, nanotube concentration and printing conditions. We report a very good alignment of the nanotubes, especially at the edges of the printed patterns, and we discuss the contributions of hydrodynamics and thermodynamics to the orientation.

Carbon nanotubes are widely used as nanocharges in polymer matrix composites for improving mechanical or electrical properties. Nanocomposites can be prepared either in the solid or in the liquid state, and in the latter case by mixing nanotubes with either melted polymers or polymer solutions. Dispersion of SWNT with high yields, as well as high amounts of individual nanotubes, can be prepared in water with the help of surfactants. However, when using such suspensions as precursors for nanocomposites, the final materials will contain some surfactants which will influence their physical properties. On the other hand, dispersing nanotubes directly in polymer solutions without using surfactants leads to low yields and poor individualization.In this work, we propose an alternative and simple way to disperse single-walled carbon nanotubes (SWNT) in aqueous solutions of two hydrosoluble polymers, polyvinyl alcohol (PVA) and polyvinyl pyrrolidone (PVP). We measure the yield using visible-NIR absorption spectroscopy, and we probe both the chemical environment of the nanotubes and the effectiveness of individualization from coupled Raman/photoluminescence studies. First, we mix aqueous suspensions of SWNT stabilized with bile salts (BS) with solutions of PVA, and we evidence a direct exchange of BS molecules and PVA chains at the surface of SWNT. By contrast, no exchange is observed with PVP. Second, we show that a simple dialysis process leads to the preparation of aqueous suspensions of SWNT covered by PVA or PVP with high yields and an effective individualization of the nanotubes. This simple method opens a new way for preparing surfactant-free polymer matrice composites with high concentrations of individual SWNT.

This study is devoted to elucidate the interplay of catalyst thickness and growth conditions in the activation and selectivity of single-walled carbon nanotube growth using cobalt deposited on Si/SiO2 as a model system. In situ Raman studies reveal that thin catalyst layers require a higher pressure of carbon precursor to initiate nanotube growth. However, if the catalysts are pre-reduced, all catalyst thicknesses display the same low threshold pressure and a higher yield of single-walled carbon nanotubes. To explain these results, catalysts formed from a gradient of cobalt thickness are studied. Surface analyses show that during the catalyst preparation, catalyst atoms at the interface with silica form small and hard-to-reduce silicate nanoparticles while the catalyst in excess leads to the formation of large oxide particles. Weakly-reducing conditions of pretreatment or synthesis are sufficient to reduce the large oxide particles and to lead to the growth of large-diameter multi-walled carbon nanostructures. However, highly-reducing conditions are required to reduce the small silicate domains into small cobalt particles able to grow single-walled carbon nanotubes. These results show that reaction of the catalyst with the support to form more refractory compounds greatly impact the nucleation yield and the growth selectivity of single-walled carbon nanotubes.

Solutions of alkali metal salts of single-walled carbon nanotubes (SWNTs) show individualization of the nanotubes without sonication-induced shortening. Bundles are fully exfoliated and length measurements show mean length over one micron, a rare case for liquid formulation of SWNTs. These concentrated solutions of individualized nanotubes in organic solvents can be freeze dried leading to ultralight, highly porous, conducting and mechanically stable carbon nanotube cryogels.