Stabilizing Membraneless Polyelectrolyte Complex Coacervates Towards Inherent Coalescence

Although recent interests in polyelectrolyte coacervates have shown their advanced applications such as microscale bioreactors with enhanced transcription rates, these applications are, however, usually limited to spatially isolated coacervate droplets or those with lipid or polymer membrane because of membraneless droplets’ instability towards coalescence. In this experimental work, we systematically explored the role of the droplet size distribution (~1-10 μm), negative to positive monomer ratio, and salt concentrations in governing the zeta potential and the long-term stability of droplets. We worked with a well-studied coacervate system: PDDA - ATP. Near-uniform size droplets were formed using a PDMS based microfluidic flow-focusing system in the laminar flow (Re<2100). As has been shown earlier, droplets with narrow size distribution had higher stability and coalesced slowly, over a period of several days, as compared to polydisperse droplets which were stable only for minutes to hours before coalescing. This work has an important consequence as this analysis allows us to understand the stability of various phase-separated liquid systems formed in vivo which finds applications ranging from protein storage to neurodegenerative diseases.