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Abstract:
The physicochemical hydrodynamics of bubbles and droplets out
of equilibrium, in particular with phase transitions, display surprisingly rich and often counterintuitive phenomena. Here we
experimentally and theoretically study the nucleation and early
evolution of plasmonic bubbles in a binary liquid consisting of
water and ethanol. Remarkably, the submillimeter plasmonic bubble is found to be periodically attracted to and repelled from
the nanoparticle-decorated substrate, with frequencies of around
a few kilohertz. We identify the competition between solutal and thermal Marangoni forces as the origin of the periodic
bouncing. The former arises due to the selective vaporization
of ethanol at the substrate’s side of the bubble, leading to a
solutal Marangoni flow toward the hot substrate, which pushes
the bubble away. The latter arises due to the temperature gradient across the bubble, leading to a thermal Marangoni flow
away from the substrate, which sucks the bubble toward it. We
study the dependence of the frequency of the bouncing phenomenon from the control parameters of the system, namely
the ethanol fraction and the laser power for the plasmonic
heating. Our findings can be generalized to boiling and electrolytically or catalytically generated bubbles in multicomponent
liquids.
