NSF Award
2423497
The propulsion of floating objects via self-generated surface tension nonuniformities, also known as Marangoni surfing, represents a fascinating phenomenon observed in the world of living organisms while also bearing promising potential for robotic applications. For example, in nature, this mode of locomotion is employed by water-walking insects for speedy movement in emergency situations and by certain bacterial swarms for rapid interfacial migration toward nutrient-rich regions for further colonization. In recent years, Marangoni surfers of various sizes have been engineered to perform a wide array of tasks, including environmental sensing and monitoring, microfluidic manipulation, and interfacial self-assembly. The goal of this project is to investigate the motion of Marangoni surfers at spherical interfaces, which are difficult to generate on Earth but achievable in zero gravity aboard the International Space Station (ISS). The propulsion of these interfacial surfers will be studied, with a specific focus on the importance of both the global interfacial curvature of the spherical water droplet and the local interface curvature around the surfers. Additionally, this project will have broader societal impacts through its integrated educational initiatives, which include outreach to underrepresented middle and high school students, research mentorship of community college and graduate students, and curriculum development.<br/><br/>The principal objective of this project is to investigate the individual and collective hydrodynamics of Marangoni surfers that self-propel on spherical interfaces. This research aims to generate new knowledge by establishing a computational-experimental framework that includes both ISS- and ground-based measurements. The framework is designed to capture the complex interactions between the motion of active particles, the transport of released species, and the effects of interface curvature and confinement. Notably, performing experiments on a levitating spherical drop in microgravity allows us to probe the importance of interface curvature on particle motion and assembly while simultaneously eliminating the local gravitationally-induced interface curvature effects from around the active particle that have been shown to play an oversized role in inter-particle interactions. The insights gained from this project are expected to define the foundational principles for designing self-propelled surfers optimized for curved interfaces, potentially leading to transformative advancements in robotics and microfluidics. Also, the results of this research will enhance our understanding of self-assembly processes, facilitating the rapid production of small-scale structured materials. Moreover, this study will shed light on the role of Marangoni stresses in the colonization of antibiotic-resistant bacteria at fluidic interfaces, offering new strategies for tackling infectious diseases by elucidating bacterial colonization and survival mechanisms in adverse conditions.<br/><br/>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.
