Melting transition of confined Lennard-Jones solids in slit pores

Abstract

The melting transition of a Lennard-Jones (LJ) system confined in slit pores of variable pore size, H, is studied using molecular dynamics simulations. We examine various mechanisms to locate the pore melting temperature under confinement using molecular simulations. Three types of structure-less pore walls are considered, namely strongly attractive walls, weakly attractive walls, and repulsive walls. In particular, we present details of the density–temperature hysteresis, Lindemann parameter, and non-Gaussian parameter for various pore sizes ranging from 8 to 3 molecular diameters. The methods as used in this work are found applicable for repulsive, weak, and moderately attractive pores. Using the above criteria, we estimated the melting temperature for various pore surfaces and pore sizes. The melting temperature, for an attractive surface, is observed to be elevated or depressed depending on the pore size. In contrast, depression in the melting temperature is observed in the case of weakly attractive and repulsive surfaces. Crossover behavior from three-dimensional to two-dimensional for weakly attractive and repulsive surfaces is proposed using the relation ΔTm ~ H−ν, with ν ranging from 0.66 to 0.81 and 1.59 to 2.1 for 2D and 3D, respectively. The methods, viz., Lindemann and non-Gaussian parameters, however, fail in predicting melting temperature for ewf > 8 and α > 4 for LJ 6-12 and LJ 9-3, surfaces, respectively.