Self-propelled colloids in soft container: from motile droplets to active emulsions

About This Grant

Non-Technical Abstract Active matter—systems composed of self-propelled particles such as bacteria or synthetic microswimmers—can behave in surprising ways when confined. For example, particles that move randomly in open space may exhibit organized, collective motion when enclosed. This project explores what happens when active particles are confined within a soft, flexible boundary like a droplet. The research team recently discovered that this setup leads to unexpected behaviors: the droplet itself spontaneously moves and deforms, driven by the activity inside. By combining theoretical modeling with controlled experiments, the investigators aim to uncover how particle motion and boundary softness interact to produce complex dynamics. Insights from this work could inform new approaches for microscale transport and control, with potential applications in soft robotics, environmental sensing, and targeted drug delivery. The project also supports interdisciplinary student training and public outreach through visually compelling experiments that mimic living systems, contributing to the growth of the STEM workforce and furthering NSF’s mission to advance scientific innovation. The project is committed to creating opportunities that are accessible to all Americans, without preference or exclusion of any individual or group. Technical Abstract This project investigates the collective dynamics of active colloidal particles confined within soft, deformable boundaries. While rigid confinement is known to strongly influence active matter behavior, the effects of soft, responsive boundaries remain poorly understood. Recent discoveries by the PIs show that Quincke rollers—synthetic self-propelled particles—encapsulated in droplets can deform the interface and drive spontaneous droplet motion, revealing a novel feedback loop between internal activity and boundary mechanics. The proposed work combines controlled experiments with theoretical modeling to explore how particle properties (e.g., density, propulsion speed, locomotion type) interact with soft confinement. Experimental observations will be complemented by microhydrodynamic models that couple particle dynamics with interfacial mechanics to uncover the physical mechanisms underlying shape changes and emergent motility. This research will advance fundamental understanding of soft active matter and may inform the design of autonomous microscale transport systems for applications in medicine, sensing, and soft robotics. The project emphasizes interdisciplinary training in theory and experiment, including collaborative opportunities at national laboratories, and supports workforce development through public outreach and engagement. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.