Dynamics of Polyelectrolyte Coacervate Droplets Under External Electric Field

Mixing oppositely charged polyelectrolytes can lead to liquid-liquid phase separation, where polymer-rich droplets (coacervates) are suspended in water, similar to oil-water emulsions. These droplets serve as a model for understanding intracellular phase separation, where similar kinds of phase separation processes lead to the formation of membraneless organelles. In this study, we explored the response of these “artificial” membraneless organelles to electric pulses as an external stimulus. The coacervate droplets were subjected to controlled low dc and ac electric fields. We found that the droplets first assumed an oblate shape and later transitioned into prolate shapes beyond a critical effective field strength. Upon discontinuation of the electric field, the droplets spontaneously returned to their initial spherical configuration. This deformation behavior is attributed to electrohydrodynamic (EHD) flows occurring within the droplets, akin to the phenomena observed in oil droplets in oil-oil suspensions. The equilibrium between electric stress, interfacial tension, and viscous forces orchestrates this deformation process. To our surprise, the extent of deformation in these artificial MLO’s was far beyond what has been observed in oil droplets.