Stability of Aqueous Suspensions of COOH-Decorated Carbon Nanotubes to Organic Solvents, Esterification, and Decarboxylation.

Carbon nanotubes are among the most widely used nanosystems, and stability of carbon nanotube suspensions is critical for nanotechnology and environmental science. Remaining in aqueous environment alone misses important factors that regulate colloidal stability in the presence of electrolytes. Indeed, introduction of (80-95) vol % organic solvents leads to sharp changes in suspension properties depending on the solvent. For example, the critical coagulation concentrations for a given inorganic or organic coagulating ion can change by 2 orders of magnitude when going from dimethyl sulfoxide to acetonitrile. We establish and explain these trends by Lewis acid-base interactions and show that a strong interaction extending beyond the standard theory of aggregation plays an important role.

Melting and crystallization temperatures in Bi-Ge nanofilms probed by a quartz Q-factor analysis.

We present a novel technique for investigating the melting and crystallization of nanomaterials in confinement. According to this method, the melting-crystallization phase transitions are traced by sharp changes of viscoelastic properties of matter using quartz resonator Q-factor analysis during heating-cooling cycles. Ge/Bi/Ge layered films, formed by successive condensation of components in high vacuum, were used as the model of nanoscale Bi confined in Ge matrix. Size dependences of the melting and crystallization temperatures have been systematically determined for the samples with Bi film thickness of 5-50 nm. The obtained data are in good agreement with the data obtained previously using in situ transmission electron microscopy techniques.