The penetrable-sphere fluid in the high-temperature, high-density limit

We consider a fluid of d-dimensional spherical particles interacting via a pair potential φ(r) which takes a finite value if the two spheres are overlapped (r < σ ) and 0 otherwise. This penetrable-sphere model has been proposed to describe the effective interaction of micelles in a solvent. We derive the structural and thermodynamic functions in the limit where the reduced temperature kBT/ and density ρσ d tend to infinity, their ratio being kept finite. The fluid exhibits a spinodal instability at a certain maximum scaled density where the correlation length diverges and a crystalline phase appears, even in the onedimensional model. By using a simple free-volume theory for the solid phase of the model, the fluid–solid phase transition is located.  2004 Elsevier B.V. All rights reserved. PACS: 61.20.-p; 64.70.Dv; 64.60.-i; 61.25.Hq