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

en This link goes to a English section zh This link goes to a Chinese section 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. 摘要 en This link goes to a English section zh This link goes to a Chinese section 聚(N-异丙基丙烯酰胺)(PNIPAM)的温敏水凝胶是软体动力领域的有力候选材料,但其迟缓的热响应动力学和有限的机械鲁棒性往往限制了其实际应用。在此,我们在PNIPAM/P(AA- co -AM)双层水凝胶中引入了磷钨酸(PTA),以调控其相变行为并增强材料性能。在该双层结构中,温敏性PNIPAM层作为动力层,而非温敏性P(AA- co -AM)层则提供机械支撑。通过将PTA的含量提高至4 wt%,PNIPAM层的热诱导变形时间从30秒延长至120秒,而在低温下的恢复时间则从120分钟缩短至60分钟,从而实现了可编程的热响应动力学。PTA有效调控了PTA-PNIPAM层的热转变行为,使其低临界溶解温度(LCST)逐渐升高且最高可调至42°C。同时,材料的热稳定性也得到提升,150°C时的质量损失明显减少。力学表征表明,P(AA- co -AM)层调节了水凝胶网络的拉伸性能,且该双层结构的性能显著优于原始PNIPAM水凝胶。得益于动力学调控与机械增韧的协同效应,该双层水凝胶进一步展现出多基底黏附性和可逆变形能力,并成功实现了水下抓取演示。本工作提出了一种基于多金属氧酸盐的水凝胶改性策略,可同时控制PNIPAM基水凝胶的热响应动力学并增强其韧性,从而推动了功能性软材料在相关应用中的发展。