Now, consider any material that (i) can undergo a first-order phase transition and (ii) is bounded by a free surface or a container wall. As one approaches the transition, the bulk material undergoes abrupt or discontinuous changes whereas the surface or interfacial region may exhibit continuous changes and critical phenomena. These latter phenomena arise if the disordered phase appears in the surface region as one approaches the phase transition even though the bulk material remains ordered.
This surface-induced disordering process was first described within molecular (or mean) field theory [1] [2] and then generalized by scaling arguments [3]. One example is provided by surface melting, which is governed by an order parameter with several components [4] [5]. Surface-induced disorder and surface melting represent wetting phenomena, in which the free surface of a solid is "wetted" by a disordered phase. [3] [6] [7]