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The functionalization of carbon nanotubes with fluorescent molecules is a standard procedure in many toxicity studies aiming at knowing their distribution within cells or whole organisms. Nevertheless, there is a lack of knowledge concerning the efficiency of the grafting processes, and more specifically concerning the question of the competition between covalent and non-covalent grafting. In this work, we investigated the grafting process of the fluorescein isothiocyanate (FITC) onto double-walled carbon nanotubes (DWNTs) using X-ray photoelectron spectroscopy, inelastic neutron scattering spectroscopy and computational simulations.We demonstrated that both covalent and non-covalent grafting occurred during the functionalization with the FITC. Moreover, we showed that a significant fraction of the fluorophore remained simply adsorbed onto the DWNTs despite thorough washing steps, which raises concerning questions about the use of this fluorophore in some toxicity studies and its possible ability to mislead their conclusions.

The spectra of liquid 85%Fe5%Ni10%S (Tm = 1650 K) and liquid 85%Fe15%Ni have been studied by means of inelastic neutron scattering. Our aim was to explore at high frequencies some observed anomalies as reported from ultrasound studies. Contrary to the behavior of the pure liquid-metals, the phase velocity of the observed excitation for the sulfur-containing sample increases with temperature while their damping decreases. On the other hand, data of the binary Fe/Ni alloy do not show such an anomalous behavior.

Dielectric spectroscopy and neutron diffraction experiments in acetone have been performed in order to clarify the dynamical behavior and the structural changes associated to the unsolved thermal transition that takes place in the solid state around 130 K. The combination of dielectric experiments with neutron diffraction reveals the existence of a dielectric process in the stable crystalline phase of acetone. The evolution with temperature of the dielectric process, within the temperature range where the peak of the heat capacity was reported, supports that the transition is not of order-disorder type. The origin of the dielectric dispersion has been assigned to structural defects in the orthorhombic crystal phase of acetone. © 2005 Elsevier B.V. All rights reserved.