Finite-size scaling study of the liquid–vapour critical point of dipolar square-well fluids

Abstract

We present a Monte Carlo simulation study in the Grand-Canonical ensemble of the liquid–vapour equilibrium of the dipolar square-well fluid for reduced dipolar moments in the range between 1 and , where ε is the square-well depth and σ the hard-core diameter. We locate the critical points using the Bruce–Wilding mixed-field finite-size scaling method. In order to obtain the phase coexistence, we use a multiple-histogram reweighting technique. Our results are consistent with previous estimations reported in the literature, showing that the reduced critical temperature increases in terms of the square-well energy unit as the dipolar moment increases, but decreases if we take as energy unit the nose-to-tail configuration dipolar interaction. On the other hand, the critical density decreases on increasing the dipolar moment. Finally, we characterize how the microscopic structure of the coexisting phases depends on the dipolar moment, paying special attention to clustering and chain formation.

Keywords:

• dipolar square-well fluid
• Monte Carlo simulation
• liquid–vapour phase transition
• critical point
• finite-size scaling

Acknowledgements

The authors would like to thank Dr. G. Orkoulas for providing the coexistence curve data for the λ = 1.5 square-well fluid from Ref. 36. We acknowledge financial support from the Ministerio de Ciencia y Tecnología (Spain) through grant VEM2003-20574-C03-02, the Ministerio de Educación y Ciencia (Spain) through grant ENE2007-68040-C03-02, and the Junta de Andalucía through ‘Plan Andaluz de Investigación’ (group FQM-205).