Bioinspired materials

Flexible magnetic aerogels

A nanocomposite of bacterial cellulose nanofibrils and cobalt ferrite nanoparticles combines the flexibility of the former with the magnetic properties of the latter.

Credit: © 2010 NPG

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.

References

  1. 1

    Olsson, R. T. et al. Making flexible magnetic aerogels and stiff magnetic nanopaper using cellulose nanofibrils as templates. Nature Nanotech. 5, 584–588 (2010).

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Withers, N. Flexible magnetic aerogels. Nature Chem (2010). https://doi.org/10.1038/nchem.835

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