Light-driven mechanical motion of a two-dimensional network of polyfluorinated surfactants having azobenzene moiety sandwiched by niobate nanosheets: Effect of pH of intercalation solution

Abstract

A hybrid composed of polyfluoroalkyl azobenzene derivative (C3F-Azo-C6H) and layered niobate nanosheet can undergo interlayer distance change and nanosheet sliding motion upon photo-irradiations. However, such morphology changes are not yet sufficiently controlled, exhibiting somewhat fluctuating results. It is necessary to clarify what kind of intercalation environment promotes the high-order architecture formation suitable for the more efficient photo-induced morphology change. In this study, we have focused on the pH conditions of intercalation solution and analyzed the nanostructure and morphology change of the hybrid fabricated under the basic (pH = 11.0) and the acidic (pH = 2.4) conditions. Intercalating C3F-Azo-C6Hs into the nanosheets under the basic condition afforded a larger interlayer distance as compared with that under the acidic condition. Furthermore, the more substantial interlayer distance change (expansion ratio: 21 %) and the nanosheet sliding (sliding distance: ∼ 200 nm) were successfully induced upon UV–vis photo-irradiations of the hybrid fabricated under the basic conditions, while the hybrid fabricated under the acidic conditions exhibited the smaller changes (interlayer expansion ratio: 0.8 % with unstable/negligible nanosheet sliding). Under the basic conditions, the nanostructure of the C3F-Azo-C6Hs bilayer having non-interdigitation of the terminal alkyl chain of the two-monolayers faced each other in the bilayer caused the substantial morphology changes such as interlayer distance change and nanosheet sliding, whereas the deeply interdigitated terminal alkyl chains in the hybrid fabricated under the acidic conditions caused only a little/negligible morphology change. Factors controlling the drastic changes of the nanostructure derived from the different fabrication conditions have been discussed.