Transition in the growth mode of plasmonic bubbles in binary liquids

Metal nanoparticles under laser irradiation can produce enormous heat due to surface plasmon resonance. When submerged in a liquid, this can lead to the nucleation and growth of plasmonic bubbles. We study the growth of plasmonic microbubbles in binary liquids via high-speed imaging. By mixing fluids with a large difference in refractive index, we can additionally visualize instantaneous, local changes in the concentration. Surprisingly, for a certain concentration range, the bubble undergoes a spontaneous transition from slow, evaporative to fast, convective growth. The transition occurs as the three-phase contact line reaches the spinodal temperature of the more volatile component of the binary liquid. This leads to massive, selective evaporation and creates a strong solutal Marangoni flow along the bubble, which marks the beginning of convective growth. After the transition the bubble starts to oscillate in position and in shape. Though different in magnitude, the frequencies of both oscillations follow the same power law f ~ (ρ/σ R³ )^-1/2, which is characteristic for bubble shape oscillations. The transitions and the oscillations both induce a strong motion in the surrounding liquid, opening doors for various applications where local mixing is beneficial.