A nanocomposite of bacterial cellulose nanofibrils and cobalt ferrite nanoparticles combines the flexibility of the former with the magnetic properties of the latter.
Biologically inspired materials often have superior properties to those made by more conventional means. Incorporating nanostructural features — for instance, polymer–nanoparticle composites — can result in multifunctional materials. This technique has proved successful for adding optical and catalytic properties, but magnetic nanoparticles have a tendency to aggregate and thus degrade other material properties.
Now, R. T. Olsson and colleagues have made a flexible magnetic aerogel by anchoring cobalt ferrite nanoparticles on bacterial cellulose nanofibres1. First, they used Acetobacter xylinum to grow a cellulose-based hydrogel in a solution of coconut milk and sugar. They then added aqueous metal salts to this template and converted them to cobalt ferrite by adding a base and heating to 90 °C. The dried 'nanopaper' had spinel-phase nanoparticles that were around 40–120 nm in diameter.
The aerogels had low densities — down to 15 kg m−3 for ones with minimal nanoparticle loading. Unlike most aerogels, they are extremely flexible, can be bent in half and take a maximum strain of 90%. Silica-based aerogels can only take a strain of a fraction of one percent. The aerogels could be deformed by a household magnet, and even bent to pick up a drop of water.
Olsson, R. T. et al. Making flexible magnetic aerogels and stiff magnetic nanopaper using cellulose nanofibrils as templates. Nature Nanotech. 5, 584–588 (2010).