Nanotechnology is becoming more versatile, thanks to methods that build nanostructures within other nanostructures

 technology – building tiny structures with nanometre dimensions – is attaining new levels of complexity. Tubes within tubes, wires within tubes, and multi-channel and branched structures within or outside of other structures are just some examples of recent innovations in ‘hierarchically structured’ nanofibres.

The term stems from the hierarchy of structures, each one contained within at least one other as part of an overall nanofibrous material.

The state of the fabrication processes is reviewed in the journal  by researchers in China led by  at .

“Hierarchically structured nanofibres hold great potential to promote new catalytic properties, which may help to reduce production costs of industry and even to produce more reliable high-performance batteries for everyday use," says Zhao.

The new properties arise from the ability to bring different structures into close proximity, exposing increased surface areas with readily controlled geometry and chemical activities.

The key to creating the complex structures is the process known as . This uses an electric field to draw thread-like streams of molten or dissolved substrate materials through shaped nozzles called . The materials then solidify into whatever complex and hierarchical structures the spinnerets dictate. The substrates used to make the fibres can be organic polymers, inorganic materials, or hybrids of the two.

Electrospinning of polymers from the molten or solution phases is not the only technique that can create hierarchical nanostructures. Others include forming the materials on templates, deposition from chemicals in the gas phase, blowing molten materials into the desired shapes, or getting structures to self-assemble.

Electrospinning, however, offers several advantages, as the authors describe. “It is the most convenient and versatile approach,” they emphasise.

The authors say that the fabrication of hierarchically structured nanofibres will offer a range of new chemical effects to be explored. “Their potential to make new catalysts and energy storage materials could eventually have a significant impact on the technologies people use in everyday life,” says Zhao.

Despite the progress and potential, Zhao cautions that significant challenges still remain. One of these is to bring more consistency to the manufacture of the spinnerets, which are currently often hand-made. Automating their production would avoid the inconsistency of hand-made products, but achieving that at the very small scales required will be difficult.

Another problem is that the electrospun structures can be rather fragile. “The next generation of these nanofibres will need to be more robust,” Zhao adds. He is convinced, however, that these challenges can be met soon.

Article details:

Zhao, Z. et al.: "," Composites Communications (2019)