Nanoscale surface of carbon nanotube fibers for medical applications: Structure and chemistry revealed by TOF-SIMS analysis

Surface structure and related chemistry understanding is a vital element in the design of high biocompatible materials since adsorption and adhesion of biological components are involved. These features are even more important in the case of nanostructured materials such as carbon nanotubes (CNTs) fibers. In our preliminary work we synthesised CNTs based fibers for medical applications. This new hybrid system combines polyvinyl alcohol (PVA) with CNTs and polylactic-co-glycolic acid (PLGA), a biodegradable copolymer. The surface properties of this material are investigated in order to guarantee a biocompatible response. Time-of-flight secondary ion mass spectrometry (TOF-SIMS) was found to be an ideal tool for fiber characterisation owing to its capacity to provide chemical specificity combined with detection limits beyond the reach of techniques previously used. Complementary morphological information is provided by atomic force microscopy (AFM). The corroboration of both data enables us to define the chemistry and structure of this new formulation.     

Spontaneous dissolution of a single-wall carbon nanotube salt

Upon reduction with alkali metals, single-wall carbon nanotubes (SWNTS) are shown to form polyelectrolyte salts that are soluble in polar organic solvents without any sonication, use of surfactants, or functionalization whatsoever, thus forming true thermodynamically stable solutions of naked SWNTs.     

Liquid Crystal Emulsions

We review recent findings about the behavior of emulsions made of droplets suspended in liquid crystalline materials. By contrast to classical emulsions, which are usually made of isotropic oils and water, liquid crystal emulsions exhibit a variety of structures result in the ordering of the continuous phase. The droplets induce the formation of topological defects and distortions that lead to strong and anisotropic elastic forces between the particles. These elastic forces govern the stability and the ordering of the particles. This is observed in aqueous emulsions as well as in non-aqueous emulsions obtained from phase separation phenomena. It is shown that phase separations in liquid crystals can lead to the formation of highly ordered arrays of uniformly sized droplets. More generally, ordered structures seen in liquid crystal emulsions are of interest as examples of topologicallv-controlled organizations; they are also of potential practical importance as a novel way to control both the stability and the structures of colloidal particles.     

Carbon nanotube fiber microelectrodes

Carbon nanotube (CNT) fibers have been used to fabricate microelectrodes with an attractive electrochemical behavior. By combining the advantages of CNT materials and fiber microelectrodes, the new material expands the scope of CNT-based electrochemical devices. The CNT fiber offers a marked decrease in the overvoltage for the NADH, dopamine, and hydrogen peroxide and circumvents NADH surface fouling effects. Heat treatment is shown to be extremely useful for activating the CNT fiber surfaces for electron transfer. SEM imaging and cyclic-voltammetric data indicate that the heat treatment leads to the removal of nonconducting residues and exposure of a "fresh" CNT surface. The new electrode material thus presents new opportunities for a wide range of electrochemical and analytical applications.     

Weak surface energy in nematic dispersions: Saturn ring defects and quadrupolar interactions

The role of surface energy in the behavior of colloidal particles in liquid crystalline phases is investigated. When the surface energy dominates, a hedgehog defect is formed and, according to an electrostatic analogy, the distortions around the particles exhibit a dipolar character. By contrast, for weaker anchoring, the configuration becomes quadrupolar as evidenced by the structure of latex clusters in lyotropic systems and the observation of defects reminiscent of Saturn rings in thermotropic systems. Received 21 June 1999     

Overtone spectroscopy of some benzaldehyde derivatives

Overtone spectrum of o, m and p-nitrobenzaldehydes and p-chlorobenzaldehyde has been studied in 2000–12000 cm⁻¹ region. Vibrational frequencies and anharmonicity constants for aryl as well as alkyl CH stretch vibrations have been determined. We have also determined the internuclear distances for the aryl CH bond in the different molecules. The small variation observed in these distances is an indication of the substitution effect. It is observed that in the case of p-disubstituted benzens, the shift in aryl CH bond is proportional to sum of the Hammet σ of the substituents. However in the case of o-disubstituted benzenes it is only 80% of the para-substituted shift.