Propelling microdroplets generated and sustained by liquid-liquid phase separation in confined spaces

Area of Science:

• Fluid dynamics
• Physical chemistry
• Materials science

Background:

• Flow transport in confined spaces is crucial for technologies like pharmaceuticals, biomedical treatments, and chemical conversions.
• Existing methods face challenges in efficiency and control for complex liquid mixtures.

Purpose of the Study:

• To investigate enhanced liquid transport in confined spaces using self-propelling microdroplets.
• To understand the mechanisms of microdroplet formation and propulsion driven by phase separation.

Main Methods:

• Utilized a ternary mixture undergoing phase separation induced by a diffusing solvent.
• Employed high-speed imaging to observe microdroplet dynamics and measure velocities.
• Analyzed the resulting flow patterns and concentration gradients.

Main Results:

• Microdroplets form spontaneously and exhibit rapid propulsion (up to ~160 μm s⁻¹) along solid surfaces.
• Propulsion is driven by sharp concentration gradients arising from localized liquid-liquid phase separation.
• Microdroplet motion generates a replenishing flow, driving the system out of equilibrium.

Conclusions:

• Self-propelling microdroplets offer a distinct and effective pathway for enhanced liquid transport in confined geometries.
• This phenomenon provides a new approach for time-effective separation and smart transport of multicomponent liquid mixtures.
• Findings pave the way for novel applications in microfluidics, chemical engineering, and materials processing.