Evidence of nanobubbles in alcohol-water mixtures via production of optically-induced breathing modes in nanofluids

When light of sufficient intensity enters a liquid close to a meniscus, thermal and mechanical effects lead to the spontaneous formation of ``leaky-faucet'' breathing modes. The modes are also associated with Marangoni convection. We have recently studied these modes in highly disperse solutions containing 80-nm gold plasmonic spheres (0.01mg/mL fill factor) in alcohol-water mixtures. Our investigations are focused on characterizing and understanding the dynamically-coupled light, heat, and electrical currents that are produced via the ``osmotic stress'' of hydration and solvation. The materials of focus are plasmonically-absorbing gold and silver nanoparticles in \textit{alcohol-water mixtures }because it has been observed that the robust breathing modes occur in such nanofluids with extremely low-power light illumination (\textless 50 mW). In addition to new nonlinear dynamics associated with the anomalous physical properties of alcohol-water mixtures-- i.e., partial molar volume, adiabatic compressibility, heat capacity , ultrasonic speed, and light scattering-- we observe evidence of the formation of nanobubbles, which agree with recent hypotheses that alcohol organic-aqueous mixtures form local 100-nm inhomogeneities described as nanobubbles.