Many-body Interaction Competition Drives Reentrant Phase Transitions

Reentrant phase transitions, in which multicomponent systems phase separate at intermediate concentrations but dissolve at experimentally accessible higher concentrations, are ubiquitous in mixtures such as biomolecular condensates. We show that introducing reversible dimerization into a multicomponent Flory-Huggins model and integrating out the dimer state generate an effective three-body repulsion that reshapes phase diagram geometry. This emergent higher-order interaction arises naturally from an interaction competition and mass-action equilibrium, providing a microscopic explanation to the previously phenomenological three-body interaction. We derive a closed-form phase boundary equation capturing phase separation and reentrant dissolution in this minimal model, and predict explicit interdependence between competition strength, emergent many-body interactions, and dissociation constants. We recover and extend the reentrant phase boundary scaling relations through interaction renormalization, with regime of validity. We apply our model to G3BP1-RNA-suramin and explain the underlying mechanisms from the physical parameters inferred from reentrant phase boundaries.