Volume stabilization of single, dye-doped water microdroplets with femtoliter resolution

Abstract

A self-control mechanism that stabilizes the size of Rhodamine B-doped water microdroplets standing on a superhydrophobic surface is demonstrated. The mechanism relies on I the interplay between the condensation rate that was kept constant and the evaporation rate induced by laser excitation, which critically depends on the size of the microdroplets. The radii of individual water microdroplets (>5 mu m) stayed within a few nano-meters during long time periods (up to 455 s). By blocking the laser excitation for 500 ms, the stable volume of individual microdroplets was shown to change stepwise.