Real-Time Monitoring of Adsorption-Induced Scrolling of Colloidal Inorganic Nanosheets

Inorganic nanotubes have attracted much attention due to their unique physicochemical properties. Nanotubes can be prepared by scrolling exfoliated nanosheets under ambient conditions. However, how the nanosheet scrolled in its colloidal state has not been experimentally visualized. In this paper, we directly observed the scrolling process of nanosheets upon adsorption of organic cations. Exfoliated flat nanosheets of niobate and clay in aqueous colloids were found to scroll by adding organic cations, such as exfoliation reagents, to the colloids. Employment of cationic stilbazolium dye enabled in situ observation of the dye adsorption and scrolling by optical microscopy based on changes in color and morphology of the nanosheets. The scrolling was promoted for nanosheets adsorbed with a stilbazolium dye with a longer alkyl chain, suggesting that the interaction between the hydrophobic parts of the dye cations is the driving force of the scrolling. This finding should encourage research on the formation of nanotubes from nanosheets and also provides important guidelines for the selection of appropriate exfoliation reagents when exfoliating nanosheets from layered crystals.