Electrostatic slowdown in kinetics of spinodal decomposition

Area of Science:

• Soft Matter Physics
• Physical Chemistry
• Materials Science

Background:

• Nonionic blends undergo macroscopic phase separation via spinodal decomposition.
• Ionic mixtures with opposing charges form electrostatically stabilized microphase separated structures.
• Understanding the dynamics of these ionic systems is crucial for biological applications.

Purpose of the Study:

• To investigate the kinetics of spinodal decomposition in ionic mixtures.
• To develop a theoretical framework incorporating short-range attraction and long-range Coulomb repulsion.
• To analyze the impact of electrostatic interactions on phase separation dynamics.

Main Methods:

• Developed a dynamical (time-dependent Ginzburg-Landau) field theory (Model B plus long-range Coulomb interactions).
• Analyzed the amplification factor R(q) in the Fourier domain.
• Extended the model to include polymer blends with monomer connectivity and Rouse dynamics.

Main Results:

• Electrostatic interactions slow spinodal decomposition by adding a term to the Cahn-Hilliard equation.
• Electrostatics suppress long-wavelength modes, reducing the window of positive growth.
• A new critical scaling of the optimal growth rate (Ropt ∼ δχ1) was observed, differing from nonionic systems.
• Cluster coarsening occurs slowly to a finite equilibrium size exceeding the initial spinodal pattern scale.

Conclusions:

• Electrostatic interactions significantly alter spinodal decomposition kinetics in ionic mixtures compared to nonionic systems.
• The findings provide insights into the dynamics of biocondensate formation in cellular environments.
• The theoretical model highlights the interplay between short-range incompatibility and long-range Coulomb forces.