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 phi(r) which takes a finite value epsilon if the two spheres are overlapped (r < sigma) 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 k(B)T/epsilon and density psigma(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 one-dimensional model. By using a simple free-volume theory for the solid phase of the model, the fluid-solid phase transition is located. (C) 2004 Elsevier B.V. All rights reserved.