Adjustable Anisotropic <scp>HEA</scp>‐<scp>DAC</scp>/<scp>NIPAM</scp> Hydrogel With Multi‐Stimuli Response to Thermal and Light

ABSTRACT Hydrogels exhibiting lower or upper critical solution temperature (LCST/UCST) behavior undergo reversible phase transitions accompanied by volumetric shrinkage or optical switching, are widely used in smart windows, anti‐counterfeiting, temperature‐sensitive robots, and other fields. Nevertheless, their application is restricted by single‐step thermal transitions inherent to isotropic polymer networks, which makes it impossible to accomplish several temperature transitions of hydrogels. Furthermore, compared to single‐stimulus response, multiple responses present additional difficulties. To address these challenges, adjustable anisotropic Poly (hydroxypropyl acrylate‐co‐acryloyloxyethyl trimethyl ammonium chloride)/Poly ( N ‐isopropyl acrylamide) (HD/NIPAM) hydrogels are prepared by limited domain swelling method. These hydrogels achieve tunable transition temperatures (−1.07°C–36.04°C) and broad transition windows (9.4°C–25.3°C) by modulating NIPAM concentration and limited thickness. Remarkably, 1 HD 20 /N 15 hydrogels exhibit exceptional time and cycle stability during their reversible transparency shift (97% to 1.8%). This performance enables applications in gradient‐selective smart windows and soft thermal indicators with spatially resolved signaling. Furthermore, through the transition of matrix hydrogel (poly(hydroxypropyl acrylate‐co‐acryloyloxyethyl trimethyl ammonium chloride) (HD) hydrogel to poly(hydroxypropyl acrylate‐co‐acryloxyethyl trimethyl ammonium dysprosium thiocyanate) (HDy) hydrogel), the transition from thermal single stimulus to thermal/light dual stimulus response was achieved due to the Dy element.