Kosmotropic effect leads to LCST decrease in thermoresponsive polymer solutions

TL;DR

This study investigates how kosmotropic cosolvents lower the LCST in thermoresponsive polymer solutions using simulations and mean-field theory, revealing the underlying energetic mechanisms.

Contribution

It introduces a combined simulation and theoretical approach to explain LCST decrease via cosolvent effects in polymer solutions.

Findings

LCST decreases with kosmotropic cosolvent addition due to reduced solvent energy.

The effect weakens with increased polymer hydrophilicity, explaining system-specific behaviors.

Mean energetic models suffice to capture the LCST decrease phenomena.

Abstract

We study the phenomena of decrease in lower critical solution temperature (LCST) with addition of kosmotropic (order-making) cosolvents in thermoresponsive polymer solutions. A combination of explicit solvent coarse-grained simulations and mean-field theory has been employed. The polymer-solvent LCST behavior in the theoretical models have been incorporated through the Kolomeisky-Widom solvophobic potential. Our results illustrate how the decrease in the LCST can be achieved by the reduction in the bulk solvent energy with addition of cosolvent. It is shown that this effect of cosolvent is weaker with increase in polymer hydrophilicity which can explain the absence of LCST decrease in PDEA, water and methanol systems. The coarse-grained nature of the models indicates that a mean energetic representation of the system is sufficient to understand the phenomena of LCST decrease.