Coacervate vesicles and double emulsions*

Coacervates are liquid-like droplets that form by phase separation of macromolecules such as charged polymers. They serve as a model for understanding intracellular phase separation. They have also been proposed as models for protocells, the precursors of living cells, because of their membraneless behavior that allows for easy transport and concentration of biomolecules such as nucleic acids based on natural partitioning. This study investigates the formation of vesicles and double emulsions of polyelectrolyte coacervates. We show that the type of polyelectrolyte, that is, their charge density and their size, can control and influence the morphology of the droplet vs. vesicles, and the morphology further emerges with time due to the coarsening of the vesicles. We found that these coacervate vesicles inflate over time, mimicking inflating balloons. We found that this growth is driven by the osmosis of water from the surroundings into the lumen of vesicles, and the rate of this osmosis can be controlled using osmolytes. Overall, our work shows how changes in the molecular properties of polyelectrolytes can give rise to different morphologies of condensates that might have been present and probably influential in the prebiotic world.