Researchers coax nanoparticles to reconfigure themselves

Seeing how nanoscale building blocks can rearrange could lead to chameleon-like properties.

University of Michigan and Indiana University researchers took an electron microscope, a sample holder and computer simulations, to envisage how materials and coatings could switch between different optical, mechanical and electronic properties.

Consider chameleons, suggests Tobias Dwyer, Michigan doctoral student in chemical engineering and co-first author of the study published in Nature Chemical Engineering. ‘Chameleons change colour by altering the spacing between nanocrystals in their skin. The dream is to design a dynamic and multifunctional system that can be as good as some of the examples that we see in biology.’

The imaging technique allows a view of how nanoparticles react to changes in their environment in real time, offering an unprecedented window into their assembly behaviour. The Indiana team first suspended nanoparticles in tiny channels of liquid on a microfluidic flow cell while they viewed the mixture under their electron microscope. This gave the nanoparticles, normally attracted to each other, enough electrostatic repulsion to push them apart and allow them to assemble into ordered arrangements. Flushing new liquids into the flow cell caused the nanoblocks to switch between the two arrangements.

An electron microscope isn’t necessary to activate the particles in practical morphable materials, the researchers said. Changes in light and pH could also serve that purpose. Further work is ongoing.