We verified the droplet composition also changes in dynamically evolving droplets by confocal microscopy using short (10.8 kDa) Cy3-labeled PSS and long Cy5-labeled PSS (404 kDa). Indeed, the merged confocal micrographs (green short PSS and magenta long PSS) show a transition of white droplets, meaning both PSS lengths are mixed in the coacervate phase in the beginning to nearly completely magenta speckles and at the end of the reaction cycle and magenta offspring droplets (Fig. , intensity line plot Fig. ). In addition, we measured the ratio between the intensities of short and long PSS of coacervate droplets 5 min and 15 min after adding fuel. Five minutes after the fuel addition, the ratio of the fluorescence intensities of the short and long PSS was roughly 1.0. After 15 minutes, the ratio shifted to 1.6, meaning the long PSS was enriched in the coacervate droplet towards the end of the reaction cycle (Fig. ). The confocal microscope findings support the hypothesized mechanism of the division that short PSS is expelled first, while more solid domains comprising the long PSS remain.