Fusion of two critical points and accelerated phase dynamics in orientational ternary mixtures

Motivated by intracellular phase separation, we theoretically investigate how molecular orientation and multi-component nature affect phase behavior. We construct a minimal model for a ternary mixture composed of isotropic (I), anisotropic (A), and solvent (s) components by combining the Flory-Huggins and Maier-Saupe theories. We obtain two main results from evaluating the phase behavior and the time evolution of the density fields. First, for certain interaction parameters, two distinct binodal lines appear in the plane of the volume fractions of the I- and A-components, and merge through their respective critical points. Second, rapid droplet formation emerges due to a weakly first-order phase transition, characterized by a discontinuity of the spinodal surface. The first result indicates the possibility of continuous transformation between the two phase-separated states. The second result suggests that anisotropic molecules can regulate phase separation kinetics. These findings might be physically general beyond biological systems.

💡 Research Summary

The paper addresses how molecular orientation and multicomponent composition influence phase behavior, a question motivated by intracellular liquid‑liquid phase separation (LLPS). The authors construct a minimal theoretical framework for a ternary mixture consisting of an isotropic protein component (I), an anisotropic (nematic‑capable) protein component (A), and an inert solvent (s). The free energy is written as a sum of an isotropic Flory‑Huggins contribution and an anisotropic Maier‑Saupe contribution:

F = N T