When Like Destabilizes Like: Inverted Solvent Effects in Apolar Nanoparticle Dispersions

Inorganic nanoparticles made of metals, semiconductors, and oxides are now used as functional components in catalysis, sensing, photovoltaics, and colour conversion in white light generation.

Many applications require the particles to be dispersed individually in organic solvents or to pass through this stage during processing.

The Widmer-Cooper and Mulvaney groups from the ARC Centre of Excellence in Exciton Science, in collaboration with partners from the Leibniz Institute for New Materials in Germany, have explained why choosing a suitable solvent for this processing is not as simple as for larger colloidal particles and can lead to unexpected behaviour.

Their findings have been published in the journal ACS Nano.

This new understanding of how molecules present on the surface of the nanoparticles affects their colloidal stability will help inform the application of nanoparticles in a wide range of technologies.

Exciton Science Director Professor Paul Mulvaney said: "One of the major focuses in nanotechnology has been the scale-up of nanocrystal production. Nanocrystals are small metallic, semiconducting or magnetic crystals less than 100nm in diameter.

“These materials have unique, size-dependent properties, which makes them useful in LEDs, solar cells and biosensors. A major challenge has been preventing aggregation of these particles during commercial production and processing.

“In this paper by Monego et al., experiment and theory are used to explain how subtle changes in solvent structure can be used to stabilise the nanocrystals at higher concentrations. 

“A key discovery is the reason for precipitation of surfactant-coated particles at low temperatures, and these findings will help scientists and engineers to make and apply these materials in new and better ways."