Identity of the van der Waals Force and the Casimir Effect and the   Irrelevance of these Phenomena to Sonoluminescence
  We show that the Casimir, or zero-point, energy of a dilute dielectric ball, or of a spherical bubble in a dielectric medium, coincides with the sum of the van der Waals energies between the molecules that make up the medium. That energy, which is finite and repulsive when self-energy and surface effects are removed, may be unambiguously calculated by either dimensional continuation or by zeta function regularization. This physical interpretation of the Casimir energy seems unambiguous evidence that the bulk self-energy cannot be relevant to sonoluminescence. 
Iver Brevik, V. N. Marachevsky, and Kimball A. Milton