Coarse-Grained Model of Entropy-Driven Demixing

Entropy-driven demixing transitions
play an important role in a
variety of phenomena in solution chemistry, in mixtures of ionic liquids,
in polymers, and in biosystems. A simple coarse-grained model of a
binary (A and B) fluid mixture of Lennard-Jones particles carrying
classical harmonic oscillators whose frequency decreases with increasing
homo-coordination separates into two nearly pure phases with increasing T, as the entropy gain in lowering the oscillators’
frequency overcomes the potential energy and ideal entropy advantage
of the homogeneous phase. We characterize features of the demixing
transition and outline physical questions that can be addressed by
this simple and inexpensive model. Besides and beyond these conceptual
points, we provide examples of how the model could be adapted to real
systems, aiming at their quantitative description by a coarse-grained
model made of particles carrying momentum, energy, and entropy.