Effects of Temperature on Amphiphilicity of Pluronic Block Copolymers in Ionic Liquid Solutions Studied with Density Functional Theory

Abstract

Understanding how ionic liquids modify the assembly and thermal behavior of amphiphilic block copolymers remains an important challenge in soft matter research. Experimental studies have shown that small structural differences between imidazolium and pyrrolidinium salts can produce markedly different shifts in micellization and cloud-point temperatures, yet the molecular origin of these effects remains unclear. Here, we combine density functional theory with temperature-dependent thermodynamic analysis to quantify pairwise binding free energies between ionic liquid ions, water, and polymer segments. The calculations reveal distinct interaction hierarchies that polymer-water and ion-water associations exhibit strong entropic sensitivity to temperature, whereas polymer-polymer and ion-polymer contacts are comparatively stable. Cation-specific binding selectivity between PEO and PPO segments further modulates this balance. These results identify molecular interaction trends that help rationalize how different ionic liquids modify experimentally observed cloud-point and micellization behavior. Overall, the interplay between temperature-sensitive water interactions and selective ion-polymer association emerges as an important molecular contribution to the thermal response of IL-modified block copolymer systems, offering a thermodynamic framework for interpreting and tuning cloud-point behavior.