Phosphotungstic Acid Modulated PNIPAM/P(AA‐ co ‐AM) Bilayer Hydrogels With Programmable Thermo‐Responsive Kinetics and Enhanced Toughness

ABSTRACT Thermo‐responsive hydrogels based on poly(N‐isopropylacrylamide) (PNIPAM) are promising candidates for soft actuation, yet their practical applications are often constrained by sluggish thermo‐responsive kinetics and insufficient mechanical robustness. Herein, phosphotungstic acid (PTA), a tungsten‐containing polyoxometalate, was incorporated to regulate the phase transition behavior and modulate a PNIPAM/P(AA‐ co ‐AM) bilayer hydrogel, in which the thermo‐responsive PNIPAM layer serves as the actuator whereas the non‐thermo‐responsive P(AA‐ co ‐AM) layer provides mechanical support. By increasing the PTA content up to 4 wt%, the thermally induced deformation time of the PNIPAM layer was prolonged from 30 to 120 s, whereas the recovery time at low temperature was shortened from 120 to 60 min, thereby enabling programmable thermo‐responsive kinetics. The thermal transition of the PTA‐PNIPAM layer was effectively regulated by PTA, with the lower critical solution temperature (LCST) gradually increasing and tunable up to 42°C, accompanied by an improved thermal stability manifested by reduced mass loss at 150°C. Mechanical characterization demonstrated that the P(AA‐ co ‐AM) layer modulated the tensile properties of hydrogel networks, and the bilayer configuration significantly outperformed the pristine PNIPAM hydrogel. Benefiting from the synergistic effects of kinetic regulation and mechanical modulation, the bilayer hydrogel further exhibited multi‐substrate adhesion and reversible deformation, enabling an underwater gripping demonstration. This work highlights a polyoxometalate‐enabled strategy for simultaneously controlling thermo‐responsive kinetics and toughening PNIPAM‐based hydrogels, thereby advancing functional soft materials for actuation‐related applications.