Large Scale Flow-Mediated Formation and Potential Applications of Surface Nanodroplets

Microscopic
droplets located on a solid substrate in contact with
an immiscible liquid promise a broad range of applications in miniaturized
analytical techniques, fabrication of antireflective coatings, high-resolution
near-field imaging techniques, and many others. A simple method of
producing oil nanodroplets with desirable morphology is a bottom-up
approach called solvent exchange, where nanodroplets nucleate and
grow, as a good solvent of oil is displaced by a poor solvent. In
this work, we have achieved the production of surface nanodroplets
over a large surface area on planar or curved surfaces, guided by
the principles of the solvent exchange. The droplet size is uniform
over the entire surface of a planar or curved substrate and tunable.
The production rate is extremely high at 106 nanodroplets
per second. This advance in the nanodroplet production provides a
general platform for droplet-based applications. Here we demonstrate
that the application of surface nanodroplets in microextraction of
hydrophobic solute (dye) from its highly diluted aqueous solution
and in situ detection of the dye in a simple process,
and in fabrication of highly ordered array of microlens arrays and
polymer-capped microstructures by simple processes.