Statistical fluid theory for systems of variable range interacting via triangular-well pair potential

The interest for describing the thermodynamic properties of fluids is growing in many fields from pure theoretical to those with technological applications. In this work, we have developed an analytical expression for the Helmholtz free energy of particles interacting via the triangular-well pair potential (TW), in the Barker-Henderson framework. This theoretical equation of state (EoS) uses the analytical radial distribution function of the hard-sphere (HS) fluid coupled with the Barker-Henderson perturbation theory. Thermodynamic properties as vapor-liquid coexistence, vapor pressures, internal energies and critical properties are obtained for attractive particles whose interaction potential range lies between 1.2 ≤ λ ≤ 2.6. The performance of the TW equation of state is assessed by comparing with Monte Carlo (MC) simulation data. Finally, this theoretical approach is used to model real fluids as methane, oxygen, fluoromethane and hydrogen sulfide, in a wide range of temperature and pressures.