Structure and thermodynamics of a ferrofluid bilayer

TL;DR

This study uses Monte Carlo simulations to analyze the structural and thermodynamic behavior of a dipolar hard sphere bilayer, revealing attractive interlayer energies, negative normal pressure, and strong interlayer correlations.

Contribution

It provides detailed simulation data and analytical expressions for the thermodynamics and structure of dipolar bilayers, highlighting interlayer interactions and correlations.

Findings

Interlayer energy is attractive and negligible at large separations.

Normal pressure is negative and decays as -1/h^5 with layer separation.

Strong positional and orientational correlations exist despite weak interlayer energy.

Abstract

We present extensive Monte Carlo simulations for the thermodynamic and structural properties of a planar bilayer of dipolar hard spheres for a wide range of densities, dipole moments and layer separations. Expressions for the stress and pressure tensors of the bilayer system are derived. For all thermodynamic states considered the interlayer energy is shown to be attractive and much smaller than the intralayer contribution to the energy. It vanishes at layer separations of the order of two hard sphere diameters. The normal pressure is negative and decays as a function of layer separation $h$ as $-1/h^5$. Intralayer and interlayer pair distribution functions and angular correlation functions are presented. Despite the weak interlayer energy strong positional and orientational correlations exist between particles in the two layers.