Summary Liquid-liquid phase separation (LLPS) of polymer mixtures plays a central role in the formation of synthetic soft matter and biomolecular condensate in cells. The distinction between its associative and segregative driving modes has not been consistently drawn. We investigate LLPS and interfacial properties of two LLPS modes: associative (ALLPS) and segregative (SLLPS). Analytical expressions for the critical point (CP) and binodal boundaries are derived and show excellent agreement with self-consistent field (SCF) lattice computations. Distinct thermodynamic features differentiate ALLPS from SLLPS: (1) in ALLPS, polymers co-concentrate within a single dense phase coexisting with a solvent-rich phase, whereas in SLLPS, each polymer forms a separate phase; (2) the attractive interaction per monomer in ALLPS is strongly dependent on solvent quality but is solvent independent in SLLPS; and (3) ALLPS binodals exhibit near-universal behavior, largely independent of solvent content. SCF results further show that interfacial tension increases and interfacial width decreases with distance from the CP. We provide scaling relations for both quantities. Compared with SLLPS, ALLPS displays higher interfacial tension and a thinner interface, reflecting distinct molecular organization at the liquid-liquid boundary. These findings inform the design of structured materials and the interpretation of intracellular phase behavior.
Tuinier et al. (Mon,) studied this question.