phaseseparated

Phase-separated (phaseseparated) describes a state in which a homogeneous mixture has demixed into two or more distinct phases with different compositions and properties. At equilibrium, the phases coexist under fixed temperature and pressure, separated by an interface that carries surface tension. Phase separation is favored when intercomponent interactions promote demixing rather than mixing, creating a region of the phase diagram—the miscibility gap.

Phase separation can occur via different mechanisms depending on conditions. In the metastable region, nucleation and growth of droplets lead to phase domains that slowly coarsen. In the unstable region, spinodal decomposition causes continuous concentration fluctuations to amplify, forming interconnected structures that later coarsen into discrete domains. The late-stage dynamics are often described by coarsening processes such as Ostwald ripening or droplet coalescence.

Phase diagrams map temperature, composition, and pressure at which phases coexist, featuring a binodal line and, in some cases, a spinodal line, separating single-phase from multi-phase regions. Experimental probes include optical microscopy, light scattering, and small-angle X-ray or neutron scattering to observe domain size and morphology.

Common examples include immiscible liquids such as oil and water, polymer blends that demix into rich and lean phases, and emulsions where droplets of one liquid are dispersed in another. In biology, phase separation of proteins and RNAs can form membraneless organelles such as stress granules and nucleoli, driven by multivalent interactions and intrinsically disordered regions; dysregulation is linked to diseases in some cases.

Understanding phaseseparated systems informs materials design, polymer science, and cellular biology, with tunable morphology achieved through temperature, concentration, additives, or crosslinking.