Self-propelling Microdroplets Generated and Sustained by Liquid-liquid Phase Separation in Confined Spaces

TL;DR

This study demonstrates how self-propelling microdroplets formed by liquid-liquid phase separation can enhance flow transport in confined spaces, offering new insights for efficient separation and transport in various technological applications.

Contribution

It introduces a novel mechanism of microdroplet self-propulsion driven by phase separation, enabling enhanced liquid transport in confined environments.

Findings

Microdroplets grow, break up, and propel at speeds up to ~160 um/s.

Self-propulsion induces a replenishing flow that sustains phase separation.

The process enables repeated cascade events for enhanced flow motion.

Abstract

Flow transport in confined spaces is ubiquitous in technological processes, ranging from separation and purification of pharmaceutical ingredients by microporous membranes and drug delivery in biomedical treatment to chemical and biomass conversion in catalyst-packed reactors and carbon dioxide sequestration. In this work, we suggest a distinct pathway for enhanced liquid transport in a confined space via self-propelling microdroplets. These microdroplets can form spontaneously from localized liquid-liquid phase separation as a ternary mixture is diluted by a diffusing poor solvent. High speed images reveal how the microdroplets grow, break up and propel rapidly along the solid surface, with a maximal velocity up to ~160 um/s, in response to a sharp concentration gradient resulting from phase separation. The microdroplet self-propulsion induces a replenishing flow between the walls of the confined space towards the location of phase separation, which in turn drives the mixture out of equilibrium and leads to a repeating cascade of events. Our findings on the complex and rich phenomena of self-propelling droplets suggest an effective approach to enhanced flow motion of multicomponent liquid mixtures within confined spaces for time effective separation and smart transport processes.