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Self-coacervation, driven by polyampholytes, is crucial for biological structures and industrial applications. Simulations reveal small ions contribute minimally to this phase separation, challenging prior entropy-driven theories.

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Area of Science:

  • Physical Chemistry
  • Biophysics
  • Materials Science

Background:

  • Self-coacervation is a liquid-liquid phase separation of polyampholytes.
  • It forms membraneless organelles in vivo and synthetic materials.
  • Previously, it was thought to be driven by counter-ion release entropy.

Purpose of the Study:

  • To investigate the role of small ions in polyampholyte self-coacervation.
  • To determine the contribution of salt partitioning to phase separation.
  • To explore the impact of charge distribution on coacervation.

Main Methods:

  • Fully fluctuating field-theoretic simulations with complex Langevin sampling.
  • Complementary molecular dynamics simulations.
  • Comparison with random phase approximation (RPA) and scaling theories.

Main Results:

  • Small ions contribute weakly to self-coacervation of charge-symmetric polyampholytes.
  • Salt partitioning between phases is negligible in the weak-binding regime.
  • Charge asymmetries lead to suppressed phase separation at low salt.

Conclusions:

  • Entropy from counter-ion release is not the primary driver of self-coacervation.
  • Charge distribution significantly influences polyampholyte phase behavior.
  • Field-theoretic and particle simulations provide insights beyond RPA limitations.