Dynamics of Thermal Transport in Suspensions of Self-Propelled Microparticles*

Active colloids (0.1-10 μm in size) propel themselves through liquids using energy they harvest from their surroundings (usually in the form of a chemical fuel or incident light).  They can move in externally-guided trajectories, swim at hundreds of times their body length per second, and tow cargo several times their size.  Thus, they are being considered for a variety of applications including targeted drug delivery and environmental remediation.  Here, we use molecular dynamics (MD) and continuum simulations to analyze the effect of the active colloids’ motion on transport of thermal energy through the fluid.  MD simulations reveal the contributions of individual particles to thermal transport; continuum simulations illuminate the effect of hydrodynamic interactions among individual swimmers, allow parametric studies of swimmer speed and volume fraction, and enable estimation of macroscopic suspension properties, which can be compared with experimental measurements.  We compare the effective thermal conductivity for active suspensions with those of suspensions of non-swimming particles and to the solvents alone.