Electrostatic Correlations and Temperature-Dependent Dielectric Constant Can Model LCST in Polyelectrolyte Complex Coacervation

Abstract

The ability of polyelectrolytes to condense into a liquidlike, polyelectrolyte-rich phase out of a dilute supernatant phase through complex coacervation has led to fascinating phenomena, such as membraneless organelles and self-assembled capsules for drug delivery. Recent experiments have demonstrated that heating above a lower critical solution temperature (LCST) can drive complex coacervation. Here, we show that a coarse-grained model of electrostatic correlations is sufficient to model an LCST when accounting for the empirical decrease in the dielectric constant of the solvent upon heating. The predictions of the model agree qualitatively with experimental measurements of the compositions of the coexisting coacervate and supernatant phases. The model also achieves modest quantitative agreement with experiments, despite incorporating no other experimental parameters besides the dielectric constant and a fitted length scale. This agreement underscores the important role that can be played by electrostatic correlations in driving complex coacervation above an LCST.