Phase coexistence in nanoscopically thin films confined by asymmetric walls.

EZEQUIEL V ALBANO; K. BINDER,

Journal of Statistical Physics

Springer Verlag

Lugar: Heildelberg; Año: 2009 vol. 135 p. 991 - 1008

0022-4715

Thin Ising films with nearest-neighbor ferromagnetic exchange in a bulk magneticfield H are studied in a L × L × D geometry, where at the opposite walls, givenby the L × L surfaces, local magnetic fields H1, and HD act. While in previous work, thesymmetric case H1 = HD (leading to “capillary condensation”, when one applies the latticegas terminology) as well as the antisymmetric case H1 =−HD (leading to “interface localizationtransitions”) were studied, we focus here on the general ‘asymmetric’ case. MonteCarlo simulations are carried out and analyses based on thermodynamic integration methodsare used to establish the phase diagrams and study the properties of the coexisting phases.A discussion is given why for the range of thicknesses that is explored (16 ≤ D ≤ 80 latticespacings) this is the most suitable methodology. Restricting attention to cases wherein the semi-infinite system a first-order wetting transition occurs, it is shown that the latter,due to confinement, is turned in a thin-film triple point. Above the triple point, narrow twophasecoexistence curves are found, which are the analog of prewetting transitions in thesemi-infinite system. A comparison to related results for (symmetrical) polymer blends and(asymmetric) colloid-polymer mixtures is made.