Emulsion patterns in the wake of a liquid-liquid phase separation front

Area of Science:

• Physical Chemistry
• Materials Science
• Fluid Dynamics

Background:

• Miscible liquids undergo phase separation upon composition change.
• Bulk fluid demixing occurs at molecular scales, coarsening into macroscopic phases.
• Confined mixtures in microfluidic droplets exhibit distinct phase separation behaviors.

Purpose of the Study:

• To investigate the self-organization of liquid-liquid phase separation in microfluidic droplets.
• To develop a theoretical model predicting pattern formation and dynamics.
• To explore potential material applications of controlled phase separation.

Main Methods:

• Development of a modified Cahn-Hilliard model.
• Analysis of immiscibility front dynamics with stretched exponential behavior.
• Formulation of a scaling law for layer lifetime prediction.

Main Results:

• Microfluidic droplets show sequential phase separation bursts forming self-similar, scale-free rings of oil and water.
• The modified Cahn-Hilliard model quantitatively predicts layer spacing.
• A scaling law accurately predicts the stepwise release of inner droplets.
• Large-scale oil and water stripes form in rectangular capillaries over hours.

Conclusions:

• The study provides a quantitative theoretical framework for understanding nonequilibrium pattern formation in confined liquid-liquid phase separation.
• The findings offer insights into stepwise droplet release and large-scale stripe formation.
• Controlled liquid-liquid phase separation has potential applications in diverse fields like cell encapsulation and surface patterning.