Interfacial properties of square-well chains from molecular dynamics simulation

Abstract

Square-well (SW) potential is likely the simplest potential describing attractive and repulsive interactions. However, its discontinuous functional form makes it difficult to be used in Molecular Dynamics (MD) simulation, particularly with commercial MD packages. Recently, Zerón and collaborators [Mol. Phys. 116, 3355 (2018)] have presented a parameterisation of the SW potential that allows its use for simulation packages since the intermolecular potential and force are described by continuous mathematical functions. It was validated for SW spheres. In this work, we use this reported continuous SW potential to describe for the first time the equilibrium and interfacial properties of SW chains, with potential ranges of 𝜆=1.5 and 1.75. Simulations for tetramers interacting with 𝜆=1.5 are compared with available computational data in the literature, which has allowed to validate the method for molecular chain systems. Besides, a systematic study for the potential range of 𝜆=1.75 has not been addressed so far, which represents valuable information for instance to discern whether different microscopic theories are capable of describing this type of system. In particular, we assess the effect of temperature, chain length, and potential range on the calculated properties, namely density profiles, coexistence densities, vapour pressures, surface tensions and critical points. Overall, with increasing the chain length, the width of the envelope of the coexistence phase increases, which results in an increase of the surface tension as well as the critical temperature at the same time that the vapour pressure and the interfacial width decrease.