Phase separation bursting and symmetry breaking inside an evaporating droplet; formation of a flower-like pattern

Abstract

Pattern formation inside a liquid phase is a phenomenon involved in many different aspects of life on our planet. The droplet form of a liquid that evaporates can reveal patterns that depend on the chemistry of the droplet and the physical parameters involved. We observed a flower-like deposition pattern of micrometer-sized particles as a result of the evaporation of a droplet containing salt and a non-ionic polymer. We show experimentally that the phase separation of the polymer due to the salting-out effect causes a strong entropic flow, which manifests as vortices. The flow is called phase separation bursting flow, which leads to the axial symmetry breaking and the formation of a radially aligned flower-like pattern. We foresee that understanding the observed flow can provide insights into the fluid physics aspects of phase separation and may have implications for technical applications.