Theory and simulation for associating cyclic molecules

Abstract

A successful equation of state for ring molecules [J. Chem. Phys. 101, 6880 (1994); Phys. Rev. E 50, 386 (1994)] is extended using Wertheim's first-order thermodynamic perturbation theory to predict the degree of bonding and thermodynamic properties of associating cyclic molecules. This new theory is tested against molecular simulation results for pure fluids of cyclic trimers with either one or three association sites. The trimers’ association potential of interaction is modeled by an orientation-dependent square-well, and the segment–segment interactions are of the hard-sphere type. A wide range of densities and temperatures is studied. Values for fraction of molecules not bonded, configurational internal energy and compressibility factor were obtained using Metropolis Monte Carlo simulations in the canonical and isothermal–isobaric ensembles. The theory predictions are in excellent agreement with these simulation results.

Keywords:

• associating fluids
• intramolecular association
• thermodynamic perturbation theory
• cyclic molecules
• Monte Carlo simulation

Acknowledgements

We gratefully acknowledge financial support from the Robert A. Welch Foundation (grant C-1241), the Petroleum Research Fund, and the National Science Foundation (grant CBET-0756166). A.J.G.C. acknowledges support from Tecnológico de Monterrey (grant CAT-125).