2D versus 3D Freezing of a Lennard-Jones Fluid in a Slit Pore: A Molecular Dynamics Study

We present a computer simulation study of a (6,12)-Lennard-Jones fluid confined to a slit pore, formed by two uniform planes. These interact via (3,9)-Lennard-Jones potential with the fluid particles. When the fluid approaches the liquid-to-solid transition we first observe layering parallel to the walls. In order to investigate the nature of the freezing transition we performed a detailed analysis of the bond-orientational order parameter in the layers. We found no signs of hexatic order which would indicate a melting scenario of the Kosterlitz-Thouless type. An analysis of the mean-square displacement shows that the particles can easily move between the layers, making the crystallization a 3d-like process. This is consistent with the fact that we observe a considerable hysteresis in the heating-freezing curves, showing that the crystallization transition proceeds as an activated process.