FLUIDS IN MICROPORES .5. EFFECTS OF THERMAL MOTION IN THE WALLS OF A SLIT-MICROPORE

Previous articles in this series have concerned the prototypal slit-po re with rigin walls, in which a Lennard-Jones (12,6) monatomic film is constrained between two plane-parallel walls comprising like atoms fi xed in the face-centered-cubic (fcc) (100) configuration. The behavior of molecularly thin films in the rigid-wall prototype is governed by the template effect, whereby solid films can form epitaxially when the walls are properly aligned in the lateral directions. In this article the influence of thermal motion of the wall atoms on the template eff ect is investigated. The walls are treated as Einstein solids, the ato ms moving independently in harmonic potentials centered on rigidly fix ed equilibrium positions in the fcc (100) configuration. The force con stant f(c) is a measure of the stiffness of the walls, the rigid-wall limit being f(c) = infinity. Formal thermodynamic and statistical mech anical analyses of the system are carried out. The results of grand ca nonical ensemble Monte Carlo simulations indicate that for values of f (c) characteristic of a soft (e.g., noble-gas) crystal dynamic couplin g between wall and film has a substantial influence on such equilibriu m properties as normal stress (load) and interfacial tensions. In gene ral, the softer the walls (i.e., the smaller the value of f(c)), the w eaker the template effect and hence the softer and more disordered the confined film. (C) 1996 American Institute of Physics.