  The composition of the gaseous phase of cavitation bubbles and its role on
the collapse remains to date poorly understood. In this work, experiments of
single cavitation bubbles in aqueous ammonia serve as a novel approach to
investigate the effect of the vapor contained in a bubble on its collapse. We
find that the higher vapor pressure of more concentrated aqueous ammonia acts
as a resistance to the collapse, reducing the total energy dissipation. In line
with visual observation, acoustic measurements, and luminescence recordings, it
is also observed that higher vapor pressures contribute to a more spherical
collapse, likely hindering the growth of interface instabilities by decreasing
the collapse velocities and accelerations. Remarkably, we evidence a strong
difference between the effective damping and the energy of the shock emission,
suggesting that the latter is not the dominant dissipation mechanism at
collapse as predicted from classical correction models accounting for slightly
compressible liquids. Furthermore, our results suggest that the vapor inside
collapsing bubbles gets compressed, consistently with previous studies
performed in the context of single bubble sonoluminescence, addressing the
question about the ability of vapors to readily condense during a bubble
collapse in similar regimes. These findings provide insights into the
identification of the influence of the bubble content and the energy exchanges
of the bubble with its surrounding media, eventually paving the way to a more
efficient use of cavitation in engineering and biomedical applications.
