  The Universe is modeled as a binary mixture whose constituents are described
by a van der Waals fluid and by a dark energy density. The dark energy density
is considered either as the quintessence or as the Chaplygin gas. The
irreversible processes concerning the energy transfer between the van der Waals
fluid and the gravitational field are taken into account. This model can
simulate: (a) an inflationary period where the acceleration grows exponentially
and the van der Waals fluid behaves like an inflaton; (b) an inflationary
period where the acceleration is positive but it decreases and tends to zero
whereas the energy density of the van der Waals fluid decays; (c) a decelerated
period which corresponds to a matter dominated period with a non-negative
pressure; and (d) a present accelerated period where the dark energy density
outweighs the energy density of the van der Waals fluid.
