Strain-Induced Self-Rolling of Electrochemically Deposited Co(OH)2 Films into Organic-Inorganic Microscrolls

Strain-induced self-folding is a ubiquitous phenomenon in biology, but is rarely seen in brittle geological or synthetic inorganic materials. We here apply this concept for the preparation of three-dimensional free-standing microscrolls of cobalt hydroxide. Electrodeposition in the presence of structure-directing water-soluble polyelectrolytes interfering with solid precipitation is used to generate thin polymer/inorganic hybrid films, which undergo self-rolling upon drying. Mechanistically, we propose that heterogeneities with respect to the nanostructural motifs along the surface normal direction lead to substantial internal strain. A non-uniform response to the release of water then results in a bending motion of the two-dimensional Co(OH)(2) layer accompanied by dewetting from the substrate. Pseudomorphic conversion into Co3O4 affords the possibility to generate hierarchically structured solids with inherent catalytic activity. Hence, we present an electrochemically controllable precipitation system, in which the biological concepts of organic matrix-directed mineralization and strain-induced self-rolling are combined and translated into a functional material.

Automated summary

In this study, free-standing three-dimensional microscrolls of cobalt hydroxide were prepared using the concept of strain-induced self-folding. The electrodeposition of thin polymer/inorganic hybrid films in the presence of structure-directing water-soluble polyelectrolytes resulted in the self-rolling of the films upon drying. The internal strain and non-uniform response to water release were proposed as the underlying mechanisms. The pseudomorphic conversion into Co3O4 allowed the generation of hierarchically structured solids with inherent catalytic activity. This research presents an electrochemically controllable precipitation system that combines the concepts of organic matrix-directed mineralization and strain-induced self-rolling, providing a new approach for the design of functional materials.