posted on 2020-03-18, 20:04authored byPeter R. Birkin, Steven Linfield, Jack J. Youngs, Guy Denuault
Nanobubbles
are fascinating but controversial objects. Although
there is strong evidence for the existence of surface bound nanobubbles,
the possibility of stable nanobubbles in the bulk remains in question.
In this work, we show how ultrasonication of electrolytes can create
transient bulk nanobubbles. To do this, glass nanopores are used as
Coulter counters to detect nanobubbles. During ultrasonication, these
transient bulk nanobubbles are shown to exist in relatively high concentrations
while bubble activity on the surface of a solid media close to the
pore is driven by ultrasound. However, the transient nature of these
bubbles is evident upon termination of the ultrasonic source. High-speed
imaging suggests that these transient nanobubbles originate from the
fragmentation of larger bubbles,
which skate over the surface of the structure in the acoustic field
present. Transient nanobubbles as small as ∼100 nm in radius
are detected. In contrast to previous work with microbubbles, no evidence
for the oscillation of these nanobubbles during translocation was
found. The novel experimental approach presented here provides strong
evidence for the existence of transient nanobubbles in bulk solution.