Ionically Counter‐Programmable Phase‐Separation of Superstable Star‐Biopolyamide Coacervates for Electrothermally‐Responsive Pseudosolid Smart Windows

Abstract

ABSTRACT Thermoresponsive polymers are highly anticipated for passive thermochromic smart windows, yet the instability and too‐high mobility of their light‐scattering states for separated phases remain significant hurdles. To address these challenges, we report a design concept for pyrrolidone‐based star‐polyamides synthesized from itaconic acid and cadaverine, whose architecture provides exceptional sensitivity to external stimuli. In a stark departure from the classical Hofmeister series, Ca 2+ initiates an anomalous salting‐in effect that contrasts with the Na + ‐induced salting‐out. DFT/MD calculations reveal that pyrrolidone moderately coordinates with Ca 2+ without disrupting its hydration shell, thereby imparting a dense positive charge to the coacervate surfaces. Crucially, the cationic surface charge endows the coacervates with light‐scattering bodies with superior dispersion stability, surpassing conventional PNIPAM by over 20‐fold. The system maintains robust stability at 5 mol/L, a regime where conventional thermoresponsive polymers inevitably fail. An applied electric field enables spatial control of transparency, creating a dual electro‐thermal responsive system for energy‐efficient, sustainable smart windows. Furthermore, the Ca 2+ salting‐in effects enable coacervation in a high polymer concentration range over 50% to establish pseudosolidity, which provides a versatile platform for next‐generation electro‐thermal soft systems, ranging from implantable biosensors to battery‐operated smart windows.