Ionically Counter-Programmable Phase-Separation of Superstable Star-Biopolyamide Coacervates for...

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, Ca²⁺ initiates an anomalous salting-in effect that contrasts with the Na⁺-induced salting-out. DFT/MD calculations reveal that pyrrolidone moderately coordinates with Ca²⁺ 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 Ca²⁺ 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.