Regulating Electrostatic Interactions Towards Thermoresponsive Hydrogels with Low Critical Solution Temperature.

Low critical solution temperature (LCST) of commonly-used thermoresponsive polymers in water are basically dominated by hydrophobic interactions. Here, we report a novel thermoresponsive system based on electrostatic interactions. By simply loading aluminum chloride (AlCl 3 ) into non-responsive poly(2-hydroxyethyl acrylate) (PHEA) hydrogels, PHEA-Al gels turn to have reversible thermoresponsive behavior between transparent and opaque without any volume change. Further investigations by changing metal ion-polymer compositions unravel the necessity of specific electrostatic interactions, namely, cation-dipole bonding interactions between hydroxy groups and trivalent metal ions. The thermoresponsive hydrogel demonstrates high transparency (∼95%), excellent luminous modulation capability (>98%) and cyclic reliability, suggesting great potentials as energy-saving materials. Although LCST control by salt addition is widely known, salt-induced expression of thermoresponsiveness was barely discussed before. Our design provides a new approach of easy fabrication, low cost, and scalability to develop stimuli-responsive materials. This article is protected by copyright. All rights reserved.