Scaling Relations of Multicomponent Phase Coexistence Boundaries

Multicomponent phase-separating molecular systems play a key role as membraneless organelles in living cells. Phase diagrams are indispensable for probing the concentration-dependent behavior of these condensates, yet their interpretation has remained largely qualitative due to challenges of modeling complex, multicomponent interactions. Here, we present a generic framework for quantitative analysis and interpretation of phase diagrams. We derive an analytical expression for the phase boundary normal vector, which reveals two distinct scaling regimes: one for associative phase separation, characterized by a power-law scaling analogous to mass-action kinetics that allows for direct extraction of dense phase solute molar ratios, and another for condensate dissolution, where an exponential scaling quantifies three-body repulsion effects triggered by the addition of a new component. We analyze a wide range of experimentally measured phase diagrams, covering proteins NSP5, NSP2, FUS, Whi3, G3BP1, and antimicrobial peptides, and we demonstrate that the additional quantitative insights can aid the mechanistic interpretation of their phase behavior.