Tunable Hydrodynamic Interfacial Instability by Controlling a Thermodynamic Parameter of Liquid-Liquid Phase Separation

Herein, we report on the hydrodynamic interfacial instability controlled by a thermodynamic parameter driving the liquid-liquid phase separation during fluid displacement in a Hele-Shaw cell. This instability remains even when the solution is guaranteed to be hydrodynamically stable. Adjusting the salt concentration helps control the miscibility of the solutions and change the pattern of the interface. We observe stable circular, fingering, and droplet formation patterns as the salt concentration is decreased from equilibrium. In addition, we analyze this interfacial instability using thermodynamic flux, which is determined from the growth rate of the interface, and provide a theoretical framework to quantitatively predict the transition points between the patterns. We find that the patterns transition to a state having higher entropy production.

Automated summary

In this study, hydrodynamic interfacial instability controlled by a thermodynamic parameter driving liquid-liquid phase separation is reported during fluid displacement. Adjusting salt concentration controls the miscibility of solutions, changing interface patterns from stable circular to fingering and droplet formation as salt concentration decreases. The patterns transition to a state with higher entropy production.