Liquid-liquid phase separation at the interface of an evaporating droplet; formation of a regular lattice pattern

Evaporation alters the molecular interactions and leads to phase separation within the evaporating liquid. The question of whether evaporation could lead to specific phase separation at the liquid interface and eventually to the formation of patterns in small liquid volumes remains unaddressed. In this study, we investigated the liquid-liquid phase separation (LLPS) of an organic polymeric monomer in a salt-containing buffer within an evaporating sessile droplet. We observed that LLPS occurs at the dynamic interface of the droplet and leads to the formation of polymeric coacervates or regular lattice patterns depending on the initial concentration of the polymer. Our results show that the interaction of salt with the polymeric monomers at the droplet interface can lead to LLPS and the formation of regular patterns. This study suggests that the sessile droplet setup can be utilized to achieve very regular patterns as a result of LLPS.