Nonequilibrium Dynamics of Active Colloids

Self-propelled colloids are an example of an active matter system that can be precisely controlled to investigate their nonequilibrium behavior. Under blue-light illumination, the asymmetric colloids generate phoretic and osmotic driving forces that cause self-propulsion and deviate their dynamics from non-active equilibrium particles. Here, we present the thermal and non-thermal diffusion of the colloids using video microscopy, image analysis, and approaches from statistical mechanics. Using a mean-squared displacement (MSD) analysis we characterize the motion of these colloids as directed and non-directed. The velocity autocorrelation function (VACF) was also studied to investigate directional persistence. The diffusion coefficient of these colloids was calculated using both methods (MSD and VACF), and compared to particles in equilibrium. Active and thermal diffusion has been characterized, helping to indicatie transitions between random and directed motion. We have examined the efficiency of the active colloids by comparing the energy provided and dissipated in the system. This study helps set the foundation for understanding the fundamental physics of active matter and complex diffusive systems.