The principal goal of this research is to investigate the motion of active particles at fluidic interfaces due to a gradient of surface tension stemming from the discharge of a surface-active agent, a surface reaction, or from the release of heat by the particle. Powered by converting chemical energy into mechanical work, these self-propelled "Marangoni" particles, both at the individual level and as a collection, can bring to bear functionalities that resemble those of biological organisms. The findings of this study will determine the guiding principles for designing miniature self-propelled particles, which can lead to transformative innovations in robotics, microfluidics, and biomedical engineering. These tiny surfing robots can potentially execute missions that are currently very difficult or even impossible to accomplish. The results of this project will also give rise to the development of active self-assembly techniques, which can be used for rapid fabrication of small-scale structured materials. Further, the outcome of this research will shed light on the role of self-generated Marangoni stresses in the colonization and survival of antibiotic-resistant infectious bacteria living at fluidic interfaces. The new insight provided by these studies can thus facilitate the design of more effective antibiotics. Graduate students supported by the project will gain advanced training in fluid dynamics, transport and interfacial phenomena, and high-performance simulations. Educational modules on Marangoni propulsion and flow-driven self-assembly at interfaces will be created and showcased during outreach activities, in addition to being integrated into the existing engineering courses. Active involvement of underrepresented minority and female students will be pursued via educational and outreach activities.
This research will establish a fundamental understanding of the Marangoni-driven motion of active particles alone and in groups, which appear in various contexts ranging from robotics and manufacturing to biology and medicine. New knowledge will be created by introducing a comprehensive numerical-theoretical-experimental framework to examine the hydrodynamics of self-propelled interface-bound active particles. The successful completion of this project will lead to the development of a physics-based speed and stability charts for Marangoni surfers that serves as engineering guidelines for tailoring the system parameters to elicit the desired performance characteristics in a variety of applications. Additionally, the outcome of this study will advance the state-of-the-art in multi-physics computational analysis of particle-laden interfacial flows by developing a high-performance simulation technique capable of capturing the intricate interplay between the motion of the active particles, transport of released species or heat, and interface deformation and dynamics. The specific objectives of this project are: (i) characterizing the Marangoni propulsion of single particles in unbounded domains; (ii) investigating the influence of confinement on the propulsion dynamics of particles; (iii) analyzing the translational and rotational stability of self-propelled surfers; and (iv) exploring the self-assembly and collective surfing of active particles.
