A mechanism for the sphere/tube shape transition of nanoparticles with an imogolite local structure (imogolite and allophane)

Abstract : Imogolite and allophane are two strongly curved nanominerals. Indeed, imogolite has a tubular shape with a diameter of only 2.5 nm. Allophane is often presented as a spherical nanostructure with a diameter of about 5 nm. The mechanism explaining the strong curvature of these two nanominerals has been extensively discussed. However , whether or not these two nanomaterials are related to each other is not clear and the mechanism responsible for the selection between the two different shapes is not well established. In this article, we propose that imogolite and allophane are nanopolymorphs of the imogolite local structure and that the transition from spherical to tubular shape occurs at an early stage of the precipitation because of edge stress in proto-imogolite. This hypothesis for the shape selection is supported by the use of a nanomechanical model tuned to mimic the main characteristics of imogolite-like nanomaterials.