Adjustable Anisotropic HEA-DAC/NIPAM Hydrogel With Multi-Stimuli Response to Thermal and Light

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.