Spontaneous formation of hierarchically structured curly films of nickel carbonate hydrate through drying

Novel curly nickel carbonate hydrate film superstructures can be prepared for the first time via a facile drying process of the films formed on air/solution interface in the presence of double hydrophilic copolymer or polyelectrolyte additives. As-prepared curly film patches with average edge sizes of several hundred micrometers display adjustable curly features along different orientation. The coiling up degree of the film edges is strongly dependent on the polymer concentration in bulk solution. Most of these curly structures have a relatively smooth outer surface; however, the microstructures of the outer surface of curly films formed show porous network-like features. In addition, using different kinds of nickel salts can produce distinct curly film samples. A possible formation mechanism of the curly film structure has been proposed. The multiple interaction modes between nickel salt precursors and polymer can favor the self-organization of the film formed at the air/solution interface. This approach is expected to be extended for producing a variety of curly hierarchical structures.