Fig. 4. Combinatorial oils are optimized to support off-chip droplet stability and monodispersity after three screening rounds.

(Screening in each round was conducted as summarized in Figs. 1 and 2.) Between each screening round, successful oil combinations from the previous round were diversified using a genetic algorithm. (A) Optical stereomicrographs of example winning emulsions selected from each screening round. (B) Histograms of droplet sizes measured from emulsions shown in (A) highlight the fact that droplet sizes become increasingly monodisperse over successive screening rounds. (C) The percentage of screened combinatorial oils that produce stable droplets increased in successive rounds. In each round, 45 to 55 oils were screened.