Novel colloidal probes to quantify hydrodynamic and phoretic interactions

In active matter, janus microswimmers are often regarded as model systems. Composed of a chemically inert and a catalytic component, microswimmers consume the surrounding fuel and convert free energy into work by using the interfacial phenomenon of diffusiophoresis, or the migration in a gradient of chemicals. They interact in their surroundings via the fluid they move (hydrodynamics) and are mediated by the chemical gradient they generate (phoretic interactions). Common colloids are sensitive to gradients (phoresis) and are advected by flows (hydrodynamics) making it difficult to disentangle the two physical effects. We propose and synthesize a novel type of colloidal tracers with tunable phoretic mobility in order to quantify and disentangle the two effects. The detailed understanding of the interactions lay the groundwork for the design and assembly of complex machines made of machines or assembled from a multitude of active particles.