Entropic Charge Separation as a General Mechanism Arresting Nanoscale Condensate Coarsening

Area of Science:

• Soft matter physics
• Biophysics
• Polymer science

Background:

• Classical theories predict continuous growth of liquid-liquid phase separated droplets.
• Nanoscale biomolecular condensates often exhibit remarkable stability, defying classical growth models.
• Complex coacervation, involving oppositely charged macromolecules, is a common mechanism for condensate formation.

Purpose of the Study:

• To investigate the mechanisms behind the long-term stability of nanoscale biomolecular condensates.
• To identify and characterize a novel regime of condensate coarsening.
• To develop a unified model that explains both suppressed and classical droplet growth.

Main Methods:

• Combination of experimental studies, theoretical modeling, and computer simulations.
• Investigation of polymer solutions with varying chain-length asymmetry.
• Analysis of droplet size dynamics and interfacial properties.

Main Results:

• A merging-limited coarsening (MLC) regime was identified, where droplet merging significantly slows below a critical size.
• Chain-length asymmetry induces entropic interfacial charge separation, leading to electrostatic repulsion between droplets.
• Condensate growth follows an exponential, rather than power-law, trajectory, resulting in long-lived metastable states.

Conclusions:

• Merging-limited coarsening provides a general mechanism for the stability of nanoscale condensates.
• The developed framework unifies previously disparate models of droplet growth.
• This finding has broad implications for understanding condensate behavior in biological systems and synthetic materials.