Spontaneous orientational order in confined dipolar fluid films
Abstract
We report Monte Carlo simulation results for a strongly coupled dipolar softsphere (DSS) fluid confined to a nanoscopic slit pore with structureless, nonconducting walls. The central topic of our investigation are the conditions under which the pore fluid can spontaneously order into a globally polarized (i.e., ferroelectric) state. Polarized states are observed in bulk DSS fluids at sufficiently low temperatures and high densities/pressures. The confined system is simulated in the (N,L_{z},P_{∥},T) ensemble, where N is the particle number, L_{z} the wall separation, P_{∥} the pressure parallel to the walls, and T the temperature. Fixing T and P_{∥} such that the corresponding bulk system is ferroelectric, and considering confined films with various thicknesses proportional to L_{z}, we first demonstrate that the longrange orientational order persists down to L_{z}≈6σ. We then specialize to the case L_{z}=7σ, for which we investigate in detail the spatial and orientational structure as functions of P_{∥}. It turns out that the transition from the globally isotropic to the globally polarized phase occurs at significantly lower pressures/densities than in the bulk, indicating that spatial confinement can support the onset of ferroelectric order. We explain this phenomenon within the framework of a simple meanfield theory based on the assumption that confinement effectively restricts orientational fluctuations, as suggested by the Monte Carlo results.
 Publication:

Journal of Chemical Physics
 Pub Date:
 November 2002
 DOI:
 10.1063/1.1512282
 Bibcode:
 2002JChPh.117.8050K
 Keywords:

 Computerized Simulation;
 Fluid Films;
 Monte Carlo Method;
 Thin Films;
 68.15.+e;
 61.20.Ja;
 SolidState Physics;
 Liquid thin films;
 Computer simulation of liquid structure