The giant SALR cluster fluid: a review

We review recent developments in understanding the behaviour of equilibrium fluids with competing short-range attractions and long-range repulsions at low concentration. Typically, this SALR model system is used to represent solutions where at least one of the solute species interacts via a screened-coulomb potential, which includes many colloidal, nanoparticle and polyelectrolyte solutions among others. Provided neither the short-range or long-range interactions are too strong, and the concentration remains sufficiently low, then discrete spherical clusters of solute are expected, here called ‘Giant SALR clusters’. Because these clusters can themselves be disordered, as though fluid particles with a renormalised interaction, such fluids cannot be treated using standard mean field methods. Our review therefore focuses on theoretical routes that aim to overcome this difficulty. We highlight the main outcomes of these theories and discuss how they relate to soft matter and especially biology, including complex coacervates, membraneless organelles and the origin of life.