An equation of state is presented for describing thermodynamic properties of the Lennard-Jones truncated and shifted (LJTS) potential with a cut-off radius of 2.5 σ. It is developed using perturbation theory with a hard sphere reference term and labelled with the acronym PeTS (perturbed truncated and shifted). The PeTS equation of state describes the properties of the bulk liquid and vapour and the corresponding equilibrium of the LJTS fluid well. Furthermore, it is developed so that it can be used safely in the entire metastable and unstable region, which is an advantage compared to existing LJTS equations of state. This makes the PeTS equation of state an interesting candidate for studies of interfacial properties. The PeTS equation of state is applied here in two theories of interfaces, namely density gradient theory (DGT) and density functional theory (DFT). The influence parameter of DGT as well as the interaction averaging diameter of DFT are fitted to data of the surface tension of the LJTS fluid obtained from molecular simulation. The results from both theories agree very well with those from the molecular simulations.

A comprehensive molecular dynamics study of gas phase and supercritical fluid adsorption on planar walls in dispersive systems is presented. All interactions in the system are described with the Lennard-Jones truncated and shifted (LJTS) potential with a cutoff radius of 2.5 fluid diameters. The adsorption strength is characterized by the solid–fluid interaction energy and the wall density. Both parameters are varied systematically. The present work extends a previous study in which wetting in the same systems was investigated. Therefore, the contact angles are known for all studied systems. They include cases with total wetting as well as cases with partial wetting. The temperature varies between the triple point and 3 times the critical temperature of the LJTS fluid. For the systems with partial wetting, the adsorption is studied not only up to the saturation pressure but also in the metastable region. For all systems, the surface excess is determined as a function of pressure and temperature. Furthermore, data on the thickness and structure of the adsorbed layers is reported. In some of the systems, prewetting is observed.

The wetting of surfaces is strongly influenced by adsorbate layers. Therefore, in this work, sessile drops and their interaction with adsorbate layers on surfaces were investigated by molecular dynamics simulations. Binary fluid model mixtures were considered. The two components of the fluid mixture have the same pure component parameters, but one component has a stronger and the other a weaker affinity to the surface. Furthermore, the unlike interactions between both components were varied. All interactions were described by the Lennard-Jones truncated and shifted potential with a cutoff radius of 2.5σ. The simulations were carried out at constant temperature for mixtures of different compositions. The parameters were varied systematically and chosen such that cases with partial wetting as well as cases with total wetting were obtained and the relation between the varied molecular parameters and the phenomenological behavior was elucidated. Data on the contact angle as well as on the mole fraction and thickness of the adsorbate layer were obtained, accompanied by information on liquid and gaseous bulk phases and the corresponding phase equilibrium. Also, the influence of the adsorbate layer on the wetting was studied: for a sufficiently thick adsorbate layer, the wall’s influence on the wetting vanishes, which is then only determined by the adsorbate layer.

A comprehensive molecular dynamics study of gas phase and supercritical fluid adsorption on planar walls in dispersive systems is presented. All interactions in the system are described with the Lennard-Jones truncated and shifted (LJTS) potential with a cutoff radius of 2.5 fluid diameters. The adsorption strength is characterized by the solid-fluid interaction energy and the wall density. Both parameters are varied systematically. The present work extends a previous study in which wetting in the same systems was investigated. Therefore, the contact angles are known for all studied systems. They include cases with total wetting as well as cases with partial wetting. The temperature varies between the triple point and 3 times the critical temperature of the LJTS fluid. For the systems with partial wetting, the adsorption is studied not only up to the saturation pressure but also in the metastable region. For all systems, the surface excess is determined as a function of pressure and temperature. Furthermore, data on the thickness and structure of the adsorbed layers is reported. In some of the systems, prewetting is observed.

Recently, an equation of state (EoS) for the Lennard-Jones truncated and shifted (LJTS) fluid has become available. As it describes metastable and unstable states well, it is suited for predicting density profiles in vapor-liquid interfaces in combination with density gradient theory (DGT). DGT is usually applied to describe interfaces in Cartesian one-dimensional scenarios. In the present work, the perturbed LJ truncated and shifted (PeTS) EoS is implemented into a three-dimensional phase field (PF) model which can be used for studying inhomogeneous gas-liquid systems in a more general way. The results are compared with the results from molecular dynamics simulations for the LJTS fluid that are carried out in the present work and good agreement is observed. The PF model can therefore be used to overcome the scale limit of molecular simulations. A finite element approach is applied for the implementation of the PF model. This requires the first and second derivatives of the PeTS EoS which are calculated using hyper-dual numbers. Several tests and examples of applications of the new PeTS PF model are discussed.