Axisymmetric numerical simulation of self-propelled three-phase Janus droplets under thermocapillary effects

Janus droplets, characterized by their asymmetric internal structure, exhibit unique self-propulsion behaviors due to interfacial phenomena. While extensively studied in binary systems, the thermocapillary-driven dynamics of three-phase Janus droplets remain largely unexplored. In this work, we employ a high-fidelity axisymmetric multiphase flow model based on a thermodynamically consistent phase-field formulation to investigate the self-propelled motion of three-phase Janus droplets under imposed temperature gradients. Our results reveal that the morphology of the Janus droplet significantly alters the surrounding thermal field, reducing the effective temperature gradient along the fluid–fluid interface and thereby modulating the migration velocity. When only one droplet component exhibits temperature-dependent surface tension, the migration velocity decreases monotonically with increasing radius ratio, due to asymmetrical drag and reduced thermocapillary force. In contrast, when thermocapillary forces act on both droplet interfaces, nonlinear coupling between the two hemispheres generates synergistic propulsion, leading to enhanced migration. These findings provide fundamental insights into the interplay between droplet geometry, interfacial tension gradients, and thermal fields in multiphase systems.