Effect of Ionic Strength on the Bundling of Metal Oxide Imogolite Nanotubes

Significant developments have been proposed over the past decade in the synthesis of aluminosilicate and aluminogermanate imogolite-like nanotubes. But, while liquid phase synthesis is well-controlled, it is not the case for the nanotube arrangement in the dry state. In particular, nanotubes are found to self-assemble in bundles of various sizes, which may impact the properties of the final product. Here, we investigate the effect of ionic strength on bundling of aluminogermanate single-walled imogolite nanotubes (Ge-SWINT) in aqueous suspensions and in the resulting powders after solvent evaporation. The nanotube arrangement as a function of salt concentration was studied by X-ray scattering experiments and simulations. In aqueous suspension, nanotubes bundling occurs only at high ionic strength (IS > 8 × 10–2 mol·L–1), while beyond this threshold, the increase of electrostatic repulsions induces a complete stabilization of individual nanotubes. After solvent evaporation, nanotube arrangement is shown to...