Experimental evidence of the internal structure of aqueous-organic nanodroplets might give greater understanding of the structure and behaviour of nanosized atmospheric droplets. Insights into the internal structure of such droplets are important for understanding diverse processes like cloud formation and materials synthesis.

The internal structure of droplets can be likened to a core-shell structure in which an aqueous-rich core is surrounded by an organic shell. Barbara Wyslouzil and colleagues at the Ohio State University, US, carried out intricate small angle neutron scattering experiments to demonstrate that even droplets with radii as small as 10nm can exhibit this structure. 

In a result she describes as 'surprising', Wyslouzil found that her results on structured nanodroplets are consistent with the behaviour of macroscopic vapour-liquid interface systems at room temperature, even though the droplets examined are orders of magnitude smaller and highly supercooled.  

Eric Kaler, an expert in neutron scattering from the University of Delaware, US, commented, 'this work is a tour de force of scattering technique and shows for the first time how the nanostructure of a droplet can be measured.'

Wyslouzil's long-term goal is to investigate the structures of even smaller droplets with radii in the order of a nanometre, and the present work is 'a first step in that direction,' she said. While the technique used could be used for examining smaller structures, there are still barriers to overcome. 'The principal challenge is to reduce all instrumental sources of background scattering while increasing the neutron source strength,' said Wyslouzil. 'This would make it possible to examine smaller droplet sizes and reduce the time required to collect reasonable signals.'

Philip Earis