Charge Asymmetry Suppresses Coarsening Dynamics in Polyelectrolyte Complex Coacervation

Area of Science:

• Polymer science
• Soft matter physics
• Physical chemistry

Background:

• Mixing oppositely charged macromolecules induces liquid-liquid phase separation.
• This process forms a polymer-rich coacervate phase and a polymer-poor supernatant phase.
• Understanding the dynamics of this phase separation is crucial for various applications.

Purpose of the Study:

• To investigate the effect of charge asymmetry in polymers on the coarsening dynamics of liquid-liquid phase separation.
• To explore how solvent quality influences these dynamics in both symmetric and asymmetric polymer mixtures.
• To elucidate the underlying mechanisms by analyzing droplet interactions.

Main Methods:

• Preparation of polymer solutions with varying degrees of charge asymmetry.
• Observation and analysis of liquid-liquid phase separation dynamics using microscopy.
• Quantitative measurement of coarsening kinetics, including apparent growth exponents.
• Characterization of polymer-polymer and polymer-solvent interactions.

Main Results:

• Charge asymmetry significantly slows down the coarsening dynamics of coacervate phases.
• The apparent growth exponent deviates from the universal value of 1/3 observed in neutral systems and decreases with increasing charge asymmetry.
• Reduced solvent quality accelerates coarsening in asymmetric mixtures but decelerates it in symmetric mixtures.
• Analysis of droplet merging reveals distinct interaction potentials influenced by charge distribution.

Conclusions:

• Charge asymmetry is a critical parameter controlling the kinetics of macromolecular coacervate formation.
• The interplay between charge asymmetry and solvent quality offers a tunable pathway to modulate phase separation dynamics.
• Understanding droplet interaction potentials provides insight into the fundamental mechanisms governing these complex fluid systems.