Cosolvent control of lower and upper critical solution behavior in polyelectrolyte complexes

Published

July 1, 2025

Author(s)

Yuanchi Ma, Vivek Prabhu

Abstract

We report that polar cosolvent-water mixtures offer a unique approach to controlling the liquid-liquid phase separation (LLPS) of polyelectrolyte complex solutions formed from degree of polymerization-matched mixtures of strong and weak polyelectrolytes—respectively, quaternary poly(N,N-dimethylaminoethyl methacrylate chloride) (qPDMAEMA) and sodium poly(acrylate) (PA). As observed in prior work, associative LLPS in water exhibits an upper-critical salt concentration with stoichiometric complexes and lower-critical solution temperature (LCST) behavior, where electrostatic correlations are be-lieved to drive phase behavior. However, upon addition of a miscible cosolvent prior to mixing the individual polyelectro-lytes at room temperature, we observe a shift in the LCST and appearance of an upper-critical solution temperature (UCST). This new UCST feature corresponds to a segregative LLPS, whereby the polycation partitions out of the polyanion-rich dense phase and into the supernatant. This behavior arises both with cosolvents that decrease (e.g. ethylene glycol) or in-crease (e.g. N-methyl formamide) the average solvent dielectric constant, suggesting that electrostatic correlations may not primarily control the phase behavior for cosolvated coacervate systems. A conceptual 3D phase surface summarizing these observations for the cosolvated system suggests that two distinct surfaces with critical lines appear on polymer-salt-temperature phase diagram.

Citation

ACS Macro Letters

Volume

14

Pub Type

Journals

Download Paper

https://doi.org/10.1021/acsmacrolett.5c00315

Local Download

Keywords

liquid-liquid phase separation, polyelectrolyte complexation, cosolvency, cloud point

Citation

Ma, Y. and Prabhu, V. (2025), Cosolvent control of lower and upper critical solution behavior in polyelectrolyte complexes, ACS Macro Letters, [online], https://doi.org/10.1021/acsmacrolett.5c00315, https://tsapps.nist.gov/publication/get_pdf.cfm?pub_id=959993 (Accessed July 19, 2025)