  Fluid phase equilibria involving nano-dispersed phases, where at least one of
the coexisting phases is confined to a small volume, are investigated by
molecular dynamics simulation. Complementing previous studies on nanoscopic
droplets, simulation volumes containing a nanoscopic gas bubble surrounded by a
subsaturated liquid phase under tension, i.e. at negative pressure, are
conducted in the canonical ensemble. The boundary conditions are chosen such
that the phase equilibrium at the curved interface is thermodynamically stable.
Two distinct size-dependent effects are found: Curvature induces a
subsaturation of the system, leading to a smaller liquid density. For the gas
in the centre of the bubble, the small diameter has an additional obverse
effect, increasing its density. The curvature dependence of the surface tension
is discussed by evaluating average radial density profiles to obtain the excess
equimolar radius, which is found to be positive, corresponding to a negative
Tolman length.
