  We use microscopic density functional theory to study filling transitions in
systems with long-ranged wall-fluid and short-ranged fluid-fluid forces
occurring in a right-angle wedge. By changing the strength of the wall-fluid
interaction we can induce both wetting and filling transitions over a wide
range of temperatures and study the order of these transitions. At low
temperatures we find that both wetting and filling transitions are first-order
in keeping with predictions of simple local effective Hamiltonian models.
However close to the bulk critical point the filling transition is observed to
be continuous even though the wetting transition remains first-order and the
wetting binding potential still exhibits a small activation barrier. The
critical singularities for adsorption for the continuous filling transitions
depend on whether retarded or non-retarded wall-fluid forces are present and
are in excellent agreement with predictions of effective Hamiltonian theory
even though the change in the order of the transition was not anticipated.
