High-Speed Particle Motion Driven by Submicron-Scale Photothermal Bubbles

Controllable directional high-speed motion is crucial for enhancing the efficiency of assembly, enrichment, and detection of nanoscale materials dispersed in a solvent. Small-sized photothermal bubbles in degassed water can generate high-speed flows due to the steep temperature gradients. However, the effect of such high-speed flow on particle manipulation has rarely been reported. In this work, a coupled model integrating the lattice Boltzmann method and the immersed boundary method is developed to comprehensively describe the photothermal conversion, gas-liquid phase transition, fluid dynamics, and particle trajectories during particle manipulation by laser-induced photothermal bubbles on a gold film. This work reports the high-speed motion of PS nanoparticles by laser-induced submicron photothermal bubbles. Through the Marangoni convection induced at the gas-liquid interface, particles are transported toward the contact line. The resulting translational velocities of the particles reach submeters per second, far exceeding the manipulation velocities (about μm/s-scale) produced by bubbles with dimensions of tens to hundreds of micrometers. Our results reveal a unique dynamic behavior of particles: during the expansion phase of bubble generation, the induced high-speed radial flow can reach tens of meters per second, pushing PS nanoparticles away from the laser heating spot. This high-speed radial flow provides a feasible strategy for enhancing the propulsion of nanoscale and microscale swimmers. Finally, the potential of gold film surface wettability for manipulating particle velocity is further investigated. Our findings demonstrate that hydrophilic surfaces enable high-speed particle transport. The demonstrated high-speed, directional motion of nanoparticles may benefit a wide range of nano- and bioapplications and offers new insights into the field of bubble-driven manipulation.