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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 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 µm/s, in response to a sharp concentration gradient resulting from phase separation. The microdroplet 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 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.
