2 Model and Method To represent the interpolyelectrolyte complex in equilibrium with supernatant in silico, we opt for the approach used in our previous works on multi-phase polyelec-trolyte systems. We independently simulate a concentrated solution of polyelectrolytes, representing the bulk of the interpolyelectrolyte complex phase, and a salt solution, representing the bulk of the supernatant phase as captured in Figure . The two phases are indirectly coupled, as detailed in the following subsections.