Directed micro assembly of passive particles at fluid interfaces using magnetic robots

We combine strategies for passive particle assembly in soft matter with robotics to develop new means of controlled interaction. In capillary assembly, particles distort fluid interfaces and move in directions that minimize the surface area. In particular, they move along principle axes on curved interfaces to sites of high curvature via capillary migration. We propose a robot that serves as a programmable source of fluid curvature and allows the collection of passive particles. When settled on a fluid interface, the magnetic robot distorts the interface, which strongly influences curvature capillary migration. The shape of the robot dictates the interface shape. Preferred assembly site can be created by imposing high interface curvature near corners. This freedom to manipulate interface curvature dynamically and to migrate laterally on the interface creates new possibilities for directed bottom-up particle assemblies and precise manipulation of these complex assembled structures. Since the passive particles can be functionalized to sense, report and interact with their surroundings, this work paves the way to new schemes for creation and control of functionalized micro robots.