Design, fabrication, and motorization of spinning colloidal particles of custom shapes.
To achieve the fabrication of micron-sized particles of controlled and custom shapes, we have combined techniques from colloidal synthesis and 3D nano-printing. This combination has allowed us to produce micron-sized micromachines whose rotational degrees of freedom are motorized by an electrohydrodynamic instability commonly referred to as Quincke electro-rotation.
We have produced large collections of spinning bodies and studied their collective dynamics.
Active Hydraulics
When active spinning bodies are in contact with a solid surface, their spontaneous rotation can be readily converted into rolling motion. When colloidal rollers interact, they self-assemble into spontaneously flowing fluids, fluids that can flow even in the absence of pressure gradients and boundary motion (pumps). We have used this model system to lay out the basic laws of active-fluid hydraulics. To do so, we studied experimentally how colloidal roller fluid self-organizes their flows in channel networks. We showed that their emergent flow patterns are generically frustrated and degenerate as soon as the hydraulic networks include junctions with an odd coordination number. Combining experiments, theory, and numerical simulations, we explained quantitatively the geometry of active hydraulic flows using concepts and tools from frustrated magnetism.
Conditional activity
We have shown that rod-shaped spinners realize an unanticipated form of active matter. Unlike all other instances of synthetic active matter, the activity of anisotropic Quincke spinners is not a priori imposed; it is conditioned by the structure of their environment. Conditional activity is not peculiar to our rod-shaped spinners but is the hallmark of all active matter formed by living organisms. Think of a pedestrian walking in a crowded environment; its walking speed strongly depends on the local packing fraction. Combining experiments, simulations, and theory, we have shown that active liquids powered by conditional activity generically phase separate according to an unanticipated scenario.
Active cristalline solids
Conceptually, the simplest form of active matter would be a crystal assembled of active units. However, unlike liquid active matter, active crystals have strongly resisted experimental investigations. Assembling colloidal crystals from spinning colloidal particles, we have quantitatively investigated the stability of this new form of ordered active matter and explained why their melting cannot be explained from equilibrium principles.
Active metamaterials
The vast majority of active matter physics has hitherto focused on self-assembly. We initiated a paradigm shift and devised the first generation of microscopic active metamaterials assembled from active spinning machines. We are currently investigating how unprogrammed functionalities can emerge from the interactions between active micromachines.
