Energetic and Entropic Contributions to the Surface Energy of a Free-Standing Thin Film of n-Tetracontane

Abstract

The surface free energy, γμ, calculated from the chemical potential, μ, and the contribution of the internal energy to the surface energy, γU, are compared for a molecular model of a free-standing thin film of n-tetracontane. The coarse-grained chains are represented on a high-coordination lattice with a step length of 2.5 A. Each occupied site on this lattice represents a two-carbon unit of n-tetracontane. The configurations of the coarse-grained chains are governed by two types of energies. Short-range intramolecular conformations are weighted using first- and second-order interactions in the classic rotational isomeric state model of Abe et al. for polyethylene (J. Am. Chem. Soc. 1966, 88, 631). Intermolecular, as well as long-range intramolecular, interactions are weighted with a discretized Lennard-Jones potential energy function, truncated after the third shell. The contribution of these two energies to γU of the amorphous free-standing thin film is 22 erg/cm2 at 400 K. The chemical potential of the...