Dynamics of Janus Colloids in Phase Separating Solvent Mixtures

Self-propelled colloids are a model system for probing the dynamics of active matter at micron and submicron length scales. Common systems utilize the asymmetric catalytic activity of Janus particles to generate local chemical gradients that drive the motion in a catalytic medium. Previous studies showed that analogous behaviors were obtained by suspending certain Janus particles in a phase separating binary mixture due to the preferential adsorption of one of the liquid species on one side of the colloids. Utilizing the recently upgraded beamline ID02 at ESRF and fast Eiger pixel detector (up to 20,000 fps), we studied the dynamics of silica-nickel Janus colloids in phase separating quasi-binary mixture of 3-methylpyridine, water and heavy water using x-ray photon correlation spectroscopy in the ultra-small angle scattering regime. This allowed the investigation of more concentrated systems than studied by optical microscopy. Results suggest rapid arrest of active motion by dynamic clustering of Janus particles.