A simple simulation model for complex coacervates

Sai Vineeth Bobbili, Scott T. Milner

Research output: Contribution to journalArticlepeer-review

5 Scopus citations


When oppositely charged polyelectrolytes mix in an aqueous solution, associative phase separation gives rise to coacervates. Experiments reveal the phase diagram for such coacervates, and determine the impact of charge density, chain length and added salt. Simulations often use hybrid MC-MD methods to produce such phase diagrams, in support of experimental observations. We propose an idealized model and a simple simulation technique to investigate coacervate phase behavior. We model coacervate systems by charged bead-spring chains and counterions with short-range repulsions, of size equal to the Bjerrum length. We determine phase behavior by equilibrating a slab of concentrated coacervate with respect to swelling into a dilute phase of counterions. At salt concentrations below the critical point, the counterion concentration in the coacervate and dilute phases are nearly the same. At high salt concentrations, we find a one-phase region. Along the phase boundary, the total concentration of beads in the coacervate phase is nearly constant, corresponding to a “Bjerrum liquid''. This result can be extended to experimental phase diagrams by assigning appropriate volumes to monomers and salts.

Original languageEnglish (US)
Pages (from-to)9181-9188
Number of pages8
JournalSoft matter
Issue number40
StatePublished - Oct 28 2021

All Science Journal Classification (ASJC) codes

  • General Chemistry
  • Condensed Matter Physics


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