Macromolecule-like Aspects for a Colloidal Suspension of an Exfoliated Titanate. Pairwise Association of Nanosheets and Dynamic Reassembling Process Initiated from It

A layered protonic titanate of lepidocrocite-type, HxTi2-x/4□x/4O4·H2O (x ∼ 0.7; □, vacancy), has been exfoliated on the action of an aqueous solution of tetrabutylammonium (hereafter TBA) hydroxide, which resulted in a stable colloidal suspension. A colloidal aggregate centrifuged from the suspension was examined by an in situ X-ray diffraction technique under conditions where drying speed was controlled. The diffraction immediately after separation from the liquid phase was principally amorphous except for a series of sharp reflections detected in a small angle scattering region. On the basis of the line profile analysis, the latter diffraction feature was accounted for by the fundamental intersheet interference of a spacing >10 nm, which demonstrates the existence of a novel associated pair of the titanate nanosheets accommodating a large volume of water cluster between them. These XRD data provide persuasive evidence for delamination into single layers. Upon drying, the amorphous halo disappeared and changed into a well-ordered crystalline pattern. This can be explained by reassembling of the individual sheets which was initiated from the paired species. A TBA intercalated compound was finally obtained as a result of drying. The theoretical simulations on the XRD data revealed that the process involves increase of the crystallites which grows in number of the sheets but shrinks in terms of intersheet distance. The dynamic process from the colloidal nanosheets to the restacked layered structure was followed here for the first time, which throws light upon the inherent nature of "single-layer colloidal suspensions" as inorganic macromolecules.