Complex topologies in phase separated droplets predicted from universal phase diagram

TL;DR

This paper predicts universal topologies of phase-separated droplets with complex internal structures based on free energy considerations, and compares these predictions with experimental data across various biomolecular systems.

Contribution

It introduces a universal framework for predicting droplet topologies based on interfacial tension ratios and solute fractions, validated against experimental observations.

Findings

Predicted universal functions for droplet topologies.

Estimated interfacial tension ranges from experimental comparisons.

Discussed effects of kinetics and molecular weight on droplet structures.

Abstract

Phase separation of two phase separating solutes in a common solvent can result in mesoscale (micron-sized) droplets with complex topologies of the domains of each solute within each droplet. Such topologies have been observed in-vitro in systems of chromatin oligomers, biomolecular condensates, and polymeric mixtures. In these systems the solutes phase separate from the solvent into droplets due to the relatively large free energy gain, which includes the energies and entropies of mixing with the solvent. Within each droplet, further phase separation can occur between the two solutes due to an additional free energy difference that promotes their demixing; in some systems, the extent of demixing can be, in some cases, be modulated by an additional component. The minimal free energy topologies are predicted as universal functions of the interfacial tension ratios and fractions of each solute within a droplet. We compare the predictions with several experimental systems to estimate the ranges of interfacial tensions. Experimental aspects that may depend on the kinetics or molecular weight variations in the system are also discussed.