  Geometrical arguments suggest that pore-mediated nucleation happens in
general in a two-step fashion, the first step being nucleation within the pore,
the second being nucleation from the filled pore into solution [Page & Sear,
Phys. Rev. Lett. 97, 65701 (2006)]. The free energy barriers controlling the
two steps of this process show opposite dependencies on pore size, implying
that for given thermodynamic conditions there exists a pore size for which
nucleation happens fastest. Here we show, within the two- and three-dimensional
Ising lattice gas, that this preferred pore size tracks the size of the bulk
critical nucleus, up to a numerical prefactor. This observation suggests a
simple prescription for directing nucleation to certain locations within
heterogeneous porous media.
