Thermally Driven Motion of Droplets on SAM Surfaces: A Molecular Dynamics Study

Noncontact precise droplet manipulation is pivotal for nanofluidic chips, thermal management, and functional material fabrication. Here, we perform molecular dynamics simulations to investigate the motion of droplets on functionalized self-assembled monolayer (SAM) surfaces under different temperature gradient conditions. By combining interfacial force and surface tension analyses, we find that the droplet movement direction is determined by the temperature field and the interface wettability. Under identical temperature gradients, droplets on the hydrophilic surface migrate toward the cooler region, while those on the hydrophobic surface move toward the warmer region. Droplet migration speeds increase with larger temperature gradients. Hydrophobic surfaces exhibit larger migration rate changes due to reduced friction resistance between droplets and the surface. Besides, altering the initial droplet temperature can offset the influence of interfacial wettability. An increase in the initial temperature of droplets causes droplets to migrate more toward the cooler side, while a decrease in initial temperature shifts migration toward the warmer side. The hysteresis observed during the later stages of droplet movement confirms this effect. Our research deepens our understanding of nanoscale thermal and fluid coupling effects and provides a new theoretical foundation for designing controllable nanofluidic systems and thermally driven nanodevices.