Abstract
We investigate whether the liquid–vapour phase transition of strongly dipolar fluids can be understood using a model of patchy colloids. These consist of hard spherical particles with three short-ranged attractive sites (patches) on their surfaces. Two of the patches are of type A and one is of type B. Patches A on a particle may bond either to a patch A or to a patch B on another particle. Formation of an AA (AB) bond lowers the energy by ε AA (ε AB ). In the limit , this patchy model exhibits condensation driven by AB-bonds (Y-junctions). Y-junctions are also present in low-density, strongly dipolar fluids, and have been conjectured to play a key role in determining their critical behaviour. We map the dipolar Yukawa hard-sphere (DYHS) fluid onto this 2A + 1B patchy model by requiring that the latter reproduce the correct DYHS critical point as a function of the isotropic interaction strength εY. This is achieved for sensible values of ε AB and the bond volumes. Results for the internal energy and the particle coordination number are in qualitative agreement with simulations of DYHSs. Finally, by taking the limit , we arrive at a new estimate for the critical point of the dipolar hard-sphere fluid, which agrees with extrapolations from simulation.
Acknowledgement
Financial support from the Foundation of the University of Lisbon and the Portuguese Foundation for Science and Technology (FCT) under Contracts nos. POCI/FIS/55592/2004, POCTI/ISFL/2/618 and PTDC/FIS/098254/2008, as well as through Pluriannual contracts with CFTC, is gratefully acknowledged.