Role of initial precursors on the liquid-crystalline phase behavior of synthetic aluminogermanate imogolite nanotubes

Abstract

HypothesisSynthetic imogolite nanotubes form stable colloidal dispersions that may also exhibit a rich liquid-crystalline phase behavior according to the nanotube length to diameter ratio. Anisometric double-walled aluminogermanate nanotubes are now readily available through hydrothermal treatment of germanium and aluminum precursors. This work aims to assess how the self-organization behavior of these nanotubes is influenced by the nature of the precursors. ExperimentsFive different samples were synthesized by changing the precursors involved in the formation of either inner or outer walls, then fully characterized. From series of aqueous dispersions prepared by osmotic stress, we evaluated the phase behavior by coupling polarized optical observations and small-angle X-ray scattering. FindingsThe formation of anisometric nanotubes is achieved whatever the initial conditions. Their structural properties are however affected by the nature of the aluminum salt. For nanotubes synthesized with aluminum perchlorate, the dispersions present an isotropic-to-columnar phase transition with a self-organization of the nanotubes over large distances. By contrast, nanotubes synthesized with chloride and nitrate salts form only nematic or isotropic liquids and tend to group together in bi-dimensional rafts. We suggest that the different phase behaviors are related at the first order to the presence of structural vacancies in the nanotube walls.