Near‐Infrared Responsive Dual‐Network Hydrogels With Enhanced Photothermal Conversion and Reversible Deformation for Smart Applications

Tannic acid iron nanoparticles (Fe/TANP) are unique light‐responsive compounds used for reversible light‐induced phase separation behavior in various temperature‐responsive polymers and Lower Critical Solution Temperature (LCST) and Upper Critical Solution Temperature (UCST) transitions in temperature‐responsive polymers. In this study, a near‐infrared (NIR)‐responsive hydrogel based on iron tannate nanoparticles (Fe/TANP) and carboxylated multi‐walled carbon nanotubes (MWCNT‐COOH) was developed. The hydrogels were based on temperature‐sensitive poly(N‐isopropylacrylamide) (PNIPAM), and the photothermal conversion efficiency of the hydrogels was significantly improved by introducing Fe/TANP and MWCNT‐COOH as photothermal converters, and the phase transition temperature was lowered from 32°C to 27.8°C. The results show that the surface temperature of the hydrogel can be increased by 11.8°C in 210 s under NIR light irradiation, which is twice as high as that of the control. In addition, the hydrogel exhibited excellent deformation in response to NIR, bending 90° in 330 s and recovering within 35 min after the light was stopped. This hydrogel, which combines efficient photothermal conversion, fast response, and reversible deformation ability, has promising applications in the fields of light‐driven sensors and soft robotics.