  Analytical properties of the scalar expansion in the cosmic fluid are
investigated, especially near the future singularity, when the fluid possesses
a constant bulk viscosity \zeta. In addition, we assume that there is a
Casimir-induced term in the fluid's energy-momentum tensor, in such a way that
the Casimir contributions to the energy density and pressure are both
proportional to 1/a^4, 'a' being the scale factor. A series expansion is worked
out for the scalar expansion under the condition that the Casimir influence is
small. Close to the Big Rip singularity the Casimir term has however to fade
away and we obtain the same singular behavior for the scalar expansion, the
scale factor, and the energy density, as in the Casimir-free viscous case.
