Sequentially Selective Coalescence of Binary Self-Propelled Droplets upon Collective Motion

Area of Science:

• Chemical Engineering
• Materials Science
• Physical Chemistry

Background:

• Droplets as microreactors offer potential for novel material and drug synthesis.
• Autonomous droplet self-organization aids in controlling sequential and selective coalescence.
• Selective coalescence driven by collective motion of self-propelled droplets in inanimate systems is undemonstrated.

Purpose of the Study:

• To demonstrate sequentially selective coalescence using the dynamic collective pattern of self-propelled droplets.
• To investigate the stages and mechanisms of selective coalescence in an autonomous inanimate system.
• To promote a new automation technology for droplet manipulation based on spatiotemporal pattern formation.

Main Methods:

• Utilized self-propelled droplets of ethyl salicylate (ES) and butyl salicylate (BS) on an aqueous sodium dodecyl sulfate (SDS) solution.
• Observed and analyzed the collective motion and coalescence patterns of the droplets over time.
• Investigated the role of dynamic pattern formation, Laplace pressure, and interfacial instability in selective coalescence.

Main Results:

• Observed three distinct stages of selective coalescence: initial hetero-coalescence, subsequent ES droplet coalescence, and final BS droplet coalescence.
• Demonstrated that collective motion of non-identical self-propelled droplets drives sequentially selective coalescence.
• Linked coalescence selectivity to dynamic pattern formation and interfacial phenomena like Laplace pressure differences and interfacial instability.

Conclusions:

• Formulated a strategy for sequentially selective droplet coalescence using collective motion of non-identical self-propelled droplets.
• This autonomous method bypasses the need for expensive equipment or complex techniques.
• Promotes a novel automation technology for droplet manipulation leveraging spatiotemporal pattern formation under non-equilibrium conditions.