Multi-Microseconds Microbubbles Induced by Nanoseconds Pulsed-Laser Heating of Gold Nano-Particles

This study examines the effect of gold-nanoparticles (GNPs) aggregation on the formation of multimicrosecond water-vapor (WV) microbubbles (MBs) generated by nanosecond pulsed-laser heating of GNPs in water. The MBs' dynamics reveal a "dual-nature" system involving both WV phase change and the release of dissolved gases (DGs). High-speed visualization (216 kfps) captures two distinct stages in the MB lifecycle: an initial fast growth-collapse of the WV phase (multimicrosecond duration), followed by a slow collapse driven by DG release (>milliseconds). A double-exponential function effectively captures these stages, distinguishing WV and DG contributions. The prolonged WV lifetime, which differs significantly from previously reported nanosecond-scale lifetime, is strongly influenced by aggregation effects. This is supported by numerical-modeling of the heat diffusion around a plasmonically heated GNP, where aggregation is assumed to occur prior to the pulsed-laser application. Besides, a correlation found to exist between the WV's lifetime and the DGs' contribution to the overall MBs, the larger the DGs' contribution, the shorter the lifetime of the WV is, which is found to be driven by the increasing likelihood of aggregation. In summary, aggregation can either enhance or suppress plasmonic bubble generation and influence the WV lifetime or DG release. This work demonstrates the feasibility of multimicrosecond WV-MBs, which potentially can offer an extended operational window for various applications, including imaging, diagnostics, and therapeutics, and microfluidic technologies.