Microrollers meet boundaries: trapping, structure, and more
Northwestern University
Abstract
Driven suspensions, where energy is input at a particle scale, are both models for understanding general principles of out-of-equilibrium self-organization, and also materials with enormous near-term applications potential. My work is focused on magnetically-actuated suspensions; I study how these materials assemble into dynamical structures, as well as how they interact with obstacles and boundaries. While the model system we employ is very simple (spinning particles in water), the strong hydrodynamic interactions between individual particles and with nearby boundaries lead to a rich array of emergent structures. Recently, we found that even simple modulations to nearby boundaries can have dramatic consequences: a single post-shaped obstacle can act as a hydrodynamic trap, and capture a passing particle. Moreover, the strength of this trapping can be easily be tuned by adjusting either the obstacle curvature or the particle-obstacle repulsive potential. This work demonstrates the complexity of this dynamical system: microrollers can become trapped by an obstacle, this trapping is stochastic, and most surprising, it is enabled by and not destroyed by thermal fluctuations. I will close by discussing how we are using this work to understand suspension transport in more complex structured environments, as well as how we can use these particles to reconfigure their local environment.
About the speaker
Dr. Michelle Driscoll is a soft condensed matter experimentalist, and her research lies at the junction between soft-matter physics and fluid dynamics. The Driscoll lab focuses on understanding how structure and patterns emerge in a driven system, and how to use this structure formation as a new way to probe nonequillibrium systems. The lab studies emergent structures in a diverse array of driven systems, from the microscopic to larger-scale. By developing a deeper understanding of patterns and structures which emerge dynamically in a driven material, we can learn not only how these structures can be controlled, but also how to use them to connect macroscopic behavior to microscopic properties. Before coming to Northwestern, Prof. Driscoll was a postdoctoral associate at New York University, working with Paul Chaikin in the Center for Soft Matter Research. She completed her Ph.D. in 2014 with Sid Nagel at the University of Chicago.
