This NSF-CASIS project involves microgravity experiments on the International Space Station (ISS), complementary terrestrial experiments and theoretical/numerical modeling to improve understanding of active colloid transport. Active colloids move by extracting energy from their surroundings and transforming it into mechanical work. These materials have similarities with biological matter, especially for concentrated suspensions where particle-particle interactions yield collective behaviors similar to those found in nature such as swarming flocks of birds, schools of fish and bacterial colonies. Although most theoretical models pertain to an isolated particle traveling in the bulk, the weight of active colloids on Earth causes them to settle at the bottom of the experimental chamber where they translate parallel to the surface. Long term microgravity conditions on the ISS offer a unique opportunity to mitigate buoyancy and sedimentation and obtain bulk measurements that can be compared with theoretical models and elucidate the role of particle-wall interactions, which complicate terrestrial experiments. The results of this project may transform a variety of applications in biomedicine and applications at the Food-Water-Energy Nexus including colloidal assembly and bubble/droplet transport. The project is a collaboration between Colorado Mesa University (CMU) - a Primary Undergraduate Institution with a diverse student body – and Florida International University (FIU) - a research intensive Minority Serving Institution (MSI). It offers a unique opportunity to promote diversity through exposure of undergraduate students to timely research and industry collaboration with the implementation partner Space Tango. The research team will develop a module for FIU’s “Engineers on Wheels” program, which visits local schools, and will collaborate with the Eureka Science Museum and Maverick Innovation Center in Colorado.
This NSF-CASIS project will provide a comprehensive understanding of complex physical mechanisms controlling the mobility of individual active colloids and their collective behavior with two distinct goals: (1) optimizing active colloid transport, and (2) understanding effects of microgravity on collective dynamics and non-equilibrium interactions of active matter. The absence of buoyancy in microgravity is expected to resolve a conundrum in terrestrial experiments wherein theoretical models of these systems are derived for isolated particles in the bulk while experimental measurements are almost always made near a wall owing to gravity-induced sedimentation. Proximity to a wall and the accompanying particle-wall interactions (hydrodynamic, phoretic, electrostatic etc.) are often invoked as corrections to explain discrepancies between theory and experiment. However, the precise roles of particle-wall interactions cannot be isolated without comparable measurements far from the wall. Sustained microgravity conditions will enable measurement of particle mobility in the bulk, providing an experimental reference for theoretical models and insight into competing buoyancy effects and wall-particle interactions. Comparison of particle-particle interactions on Earth and on the ISS will also elucidate effects of microgravity on collective behavior in active matter and dense colloidal systems including 3D phase separation. Microgravity experiments will be complemented with terrestrial bulk measurements using optical tweezers as an external forcing mechanism, which will provide insight into other active colloid transport mechanisms (e.g., catalytic) and the applicability of such external forcing for future fundamental studies. The collaboration between FIU and CMU and the partnership with Space Tango offers a unique opportunity to engage students. Undergraduate students will participate ithrough capstone projects at FIU, while CMU students will travel to FIU and gain exposure to a research intensive institution.
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.
