Orientation of Janus particles under thermal fields: The role of internal mass anisotropy

Janus particles (JPs) are a special kind of colloids that incorporate two hemispheres with distinct physical properties. These particles feature a complex phase behavior, and they can be propelled with light by heating them anisotropically when one of the hemispheres is metallic. It has been shown that JPs can be oriented by a homogeneous thermal field. We show using multiscale simulations and theory that the internal mass gradient of the JPs can enhance and even reverse the relative orientation of the particle with the thermal field. This effect is due to a coupling of the internal anisotropy of the particle with the heat flux. Our results help rationalize previous experimental observations and open a route to control the behavior of JPs by exploiting the synergy of particle-fluid interactions and particle internal mass composition.