Stable Coulomb bubbles ?
  Coulomb bubbles, though stable against monopole displacement, are unstable at least with respect to quadrupole and octupole distortions. We show that there exists a temperature at which the pressure of the vapor filling the bubble stabilizes all the radial modes. In extremely thin bubbles, the crispation modes become unstable due to the surface-surface interaction. 
L.G. Moretto, K. Tso and G.J. Wozniak (Lawrence Berkeley National   Laboratory)