Issue 40, 2021

A simple simulation model for complex coacervates

Abstract

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.

Graphical abstract: A simple simulation model for complex coacervates

Article information

Article type
Paper
Submitted
14 Jun 2021
Accepted
16 Sep 2021
First published
17 Sep 2021

Soft Matter, 2021,17, 9181-9188

A simple simulation model for complex coacervates

S. V. Bobbili and S. T. Milner, Soft Matter, 2021, 17, 9181 DOI: 10.1039/D1SM00881A

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