  Phase transformations such as freezing typically start with heterogeneous
nucleation. Heterogeneous nucleation near a wetting transition, of a
crystalline phase is studied. The wetting transition occurs at or near a
vapour-liquid transition which occurs in a metastable fluid. The fluid is
metastable with respect to crystallisation, and it is the crystallisation of
this fluid phase that we are interested in. At a wetting transition a thick
layer of a liquid phase forms at a surface in contact with the vapour phase.
The crystalline nucleus is then immersed in this liquid layer, which reduces
the free energy barrier to nucleation and so dramatically increases the
nucleation rate. The variation in the rate of heterogeneous nucleation close to
wetting transitions is calculated for systems in which the longest-range forces
are dispersion forces.
