Phys. Rev. Lett. (in the press); preprint at http://arxiv.org/abs/1410.8574

At first sight, the standard Ising model seems rather detached from wetting — the process by which a liquid makes contact with a surface. If, however, you think of the Ising spins on a 2D lattice as defining a surface with wet (spin up) and non-wet (spin down) patches, you have a vehicle for understanding wetting phenomena.

The trick is to introduce a field that acts on the spins of the surface. Xintian Wu and colleagues performed an Ising treatment of wetting in a 2D context: a square spin lattice where the 'surface' is actually a row of spins. The authors included an extra energy term to distinguish surface from bulk spin–spin interactions. The exact solution of this system shows that the wetting transition (from a partially to a completely wet surface) is of second order, but turns first order in the limit of an infinite surface-to-bulk spin–spin interaction ratio.

When the ratio is much larger than one, the transition appears first order as the critical region decreases exponentially and is therefore practically invisible to numerical studies — calling for caution when simulating critical phenomena.