Lower Critical Solution Temperature Behavior in Polyelectrolyte Complex Coacervates

Abstract

In light of recent experimental observations of lower critical solution temperature (LCST) in polyelectrolyte complex coacervates (Ali, S. et al. ACS Macro Lett. 2019, 8, 289−293), we explore its possible mechanisms on the basis of a slight modification of our theory (Adhikari, S. et al. J. Chem. Phys. 2018, 149, 163308). We explore the consequences of the temperature dependence of the solvent dielectric constant (ε) and the solvent−polymer interaction parameter (χ) on the complex coacervates' phase behavior. The results show that the temperature dependence of the solvent dielectric constant and solvent−polymer interaction parameter can result in a complex phase behavior involving two disjoint unstable regions on the temperature (T)− polyelectrolyte concentration (ϕ p ) plane. Comparison of phase diagrams constructed for different possible temperature dependencies of ε and χ shows that the experimentally observed LCST behavior is obtained only if the solvent dielectric constant decreases and the solvent−polymer interaction parameter increases with increasing temperature. Preferential partitioning of salt into the polyelectrolyte poor phase is predicted for all possible combinations of temperature dependencies of χ and ε considered in this work.

Temperature-dependent reentrant phase transition of RNA–polycation mixtures

“…44,45 More recently, experimental observations of an LCST transition have been documented for complex coacervates 37,46,47 and theoretically discussed by Muthukumar and colleagues. 48 However, to our knowledge, our results report the first experimental observation of a thermo-responsive closed-loop phase diagram in an RNA-based complex coacervate system.…”

“…Several theories have suggested that enthalpy-driven phase separation of oppositely charged polyelectrolytes is a two-step condensation process where the second step is the phase separation and it occurs through inter-complex interactions. 35,48,[57][58][59][60] In a recent work by Muthukumar and coworkers, the authors proposed the formation of polyelectrolyte complexes with dipolar trains upon mixing of oppositely charged polyelectrolytes. 35 These complexes undergo phase separation via dipole-dipole inter-complex attraction.…”

Recent progress in the science of complex coacervation

“…173,174 In all of these efforts, connectivity is implicitly considered via the inclusion of counterion condensation, and is parameterized to match observable phase behavior. 40,97,154 Pairing has also been considered in a model by Adhikari and Muthukumar, 135,175 who model coacervation as the attraction between pairs of complexed polyelectrolytes. The advantage of these ad hoc models is that they do not require an explicit description of the locally condensed charges, and instead only need to be appropriately parameterized.…”

Atomistic simulation of weak polyelectrolytes in aqueous solution

“…Muthukumar and co-workers 1,89,91,100,[125][126] have extended eq 1.20 at a mean-field level to also account for counterions and polymer-polymer attractive interactions (due to electrostatic dipolar CHAPTER 1 interactions) and very good agreement with experimental findings regarding binodal compositions and salt partitioning in the two phases was observed. [125][126] Temperature effects on the phenomenon of complex coacervation have also been discussed in recent studies, 126,169 but these will not be considered in the present Ph.D. Thesis.…”