Invited by Laboratory of Bio-Inspired Smart Interface Science of the Technical Institute of Physics and Chemistry of the Chinese Academy of Sciences (TIPCCAS), Prof. Xuehua Zhang from RMIT University , Australia Visited TIPC CAS and gave an academic report entitled Formation and self-organization of surface nanodroplets under controlled flow conditions on Apr. 18, 2016.

Nanodroplets on a solid surface (i.e., surface nanodroplets) have practical implications for high-throughput chemical and biological analysis, lubrications, laboratory-on-chip devices, and near-field imaging techniques. Oil nanodroplets can be produced on a solid–liquid interface in a simple step of solvent exchange in which a good solvent of oil is displaced by a poor solvent.

In this work, they experimentally and theoretically investigate the formation of nanodroplets by the solvent exchange process under well-controlled flow conditions. We find significant effects from the flow rate and the flow geometry on the droplet size. We develop a theoretical framework to account for these effects. 

In the talk, Prof. Xuehua Zhang discussed a basic principle for the symmetrical arrangement of surface nanodroplets during their growth under simple flow conditions. In their model system, nanodroplets nucleate at the rim of spherical cap microstructures on a substrate. They find that, while growing, the nanodroplets self-organise into highly symmetric arrangements, with respect to position, size, and mutual distance. They show and explain how the nanodroplets acquire the symmetrical spatial arrangement during their competitive growth and why and how the competition enhances the overall growth rate of the nucleated nanodroplets. This mechanism behind the nanodroplet self-organisation promises a simple approach for the location control of droplets with a volume down to attoliters.