CAREER: Self-Organization of Micro-Particles with Light and Sound

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Non-Technical Abstract:Scientists have long known that one can dramatically alter the properties of a material by patterning it on a microscopic scale. Doing so, however, presents a major challenge: this patterning must happen at a microscopic scale but over large distances, preventing the use of direct techniques like 3D printing. There is an alternative: biological organisms are able to produce complex structure using the self-organization of basic chemical components with tuned interactions. Doing something similar with manmade materials requires a better understanding of the self-organization process, as well as practical methods for engineering forces among microscopic particles. This project explores an effect known as "optical binding", which induces complex forces between clusters of particles using light. The research team is developing new experimental and numerical tools to explore the range of active and passive structures that can be generated using this force. In addition, the researchers are conducting proof of principle research on "acoustic binding", a similar effect which uses sound instead of light. The long term aim of both efforts is to exploit these novel tools to better understand self-organization in general, as well as to enable a new generation of manmade materials for industrial, defense, and consumer applications. The project also includes efforts to increase participation of underrepresented groups in STEM fields at the middle school through graduate level through integrated education and research opportunities. In particular, the researchers are developing a new course on experimental physics for Middle and High school students in collaboration with the Bobcat Summer STEM Academy at UC Merced; rather than relying on ‘canned’ physics experiments, this course exposes students to the complete lifecycle of a scientific experiment, from design through execution and data analysis.Technical Abstract:Understanding self-organization is of interest for many fields of science, including biology, chemistry, physics, and engineering. Colloidal systems have emerged as a useful experimental platform to study this phenomenon, as various techniques exist to modify the forces between colloidal particles. Despite this, there are limits to the type of forces than can be produced: they are typically short range and can only be modified during the synthesis stage. This project is studying an effect known as optical binding, which uses light to induce multi-particle interactions which are long range, directional, pairwise non-conservative, and can be altered in real time. Additionally, the project includes proof-of-principle research on acoustic binding, which produces similar forces in an athermal and inertial regime. The research team is using novel numerical and experimental methods to study both types of force in detail and exploring how these forces modify the self-organization of many-particle systems. This provides insights into how feats of self-organization are performed in the natural world, and how they could be exploited to create new manmade materials with complex microstructure. In addition to its research aims, this project also includes integrated outreach efforts to increase participation of underrepresented groups in STEM at the middle school through graduate level through research opportunities and summer programs for students and their teachers.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.