Construction And Performance Of Multifunctional Polyacrylamide-based Composite Hydrogels With Photothermal Conversion Property

The photothermal conversion smart hydrogels can convert light energy into heat energy,triggering the responsive behavior of the hydrogel material.These smart hydrogels with photothermal conversion function have wide application in the fields of drug release,seawater desalination,and light-driven devices.However,there are some unavoidable disadvantages for the current photothermal composite smart hydrogels,such as unsatisfactory photothermal performance,slow response speed,poor mechanical properties,and single function.In order to solve these problems,this work aims to construct a novel multifunctional hydrogel with excellent photothermal conversion property.In this work,two PNIPAM-based multifunctional photothermal hydrogels were fabricated by combining poly-N-isopropylacrylamide（PNIPAM）with two-dimensional MXene and Mo O₂ as photothermal agents,respectively.Then the near-infrared（NIR）responsive hydrogel actuators with bilayer anisotropic structure were prepared.The NIR-controlled response deformation behavior and the corresponding mechanism under different media were studied,and the feasibility of the composite hydrogels as smart manipulators and strain sensors was also proved.Furthermore,the third PAM-based multifunctional photothermal hydrogel was fabricated by introducing the 2D-Mo O₂ into the SA/PAM/Ca²⁺hydrogel matrix,which also showed the NIR light responsive deformability.The strain sensor based on this composite hydrogel exhibited sensitive strain responsiveness and excellent electro-mechanical stability,which could be used for real-time human motion monitoring.The main research contents and conclusions of this paper are as follows:（1）MXene/Laponite/PNIPAM composite hydrogel with photothermal conversion propertyFirst,the MXene nanosheets with high photothermal conversion efficiency（48%）were prepared by the method of interlayer etching.The multifunctional MXene/Laponite/PNIPAM hydrogel（MXTN hydrogel）with excellent photothermal property（rising to 58°C within 150 s）,good mechanical property（ε_b=700%,b=50k Pa）,high conductivity(0.35 S m^-1),and remarkable self-healing ability was fabricated by one-step polymerization method.The bilayer MXTN hydrogel actuator exhibited fast and reversible deformation response behavior under the control of NIR light even in water,which could be used as an intelligent gripper to“capture”target object.Besides,the feasibility of the MXTN hydrogel acting as tensile and compressive strain sensor was explored.The MXTN hydrogel has good application prospects in the fields of flexible sensors,photothermal physiotherapy,and soft robots.（2）2D-Mo O₂/Laponite/PNIPAM composite hydrogel with high transmittance,and photothermal conversion propertiesFirstly,the 2D-Mo O₂ having excellent photothermal conversion efficiency（62%）and thermal stability was prepared by solid-phase reduction method.Then,for the first time,the 2D-Mo O₂ was introduced into the PNIPAM matrix to prepare multifunctional2D-Mo O₂/Laponite/PNIPAM hydrogel（MTN hydrogel）with excellent photothermal performance（rising to 68°C within 150 s）,high transparency（50%）,good flexibility（ε_b=600%）,and adhesion.The bilayer actuator prepared based on the MTN hydrogel exhibited rapid and reversible deformation response under the control of NIR light even in strong acid and alkali solutions.In addition,the MTN hydrogel could be also applied as microfluidic valve and human motion sensor.Compared with most current photothermal hydrogels,the MTN hydrogel has excellent photothermal performance and high transparency,which is more conducive to the application in the fields of transparent visualization and intelligence.（3）2D-Mo O₂/SA/PAM/Ca²⁺composite hydrogel with excellent strength,high transmittance,and photothermal conversion propertiesThe 2D-Mo O₂ was introduced into the SA/PAM hydrogel system,and the multifunctional 2D-Mo O₂/SA/PAM/Ca²⁺composite hydrogel（MDN hydrogel）with excellent photothermal conversion performance（rising to 60°C within 150 s）,robust mechanical property（ε_b=1800%,b=350 k Pa）,high transparency（60%）,good electrical conductivity(0.85 S m^-1),and frost resistance（-22.4°C）was prepared by the immersion method.The MDN hydrogel actuator exhibited NIR light responsive deformability.Moreover,the flexible strain sensor prepared based on the MDN hydrogel showed sensitive and rapid strain responsiveness（GF=7.1,ε=500%）,superb electro-mechanical response stability（200 cycles）,and it could be used for real-time human motion monitoring.The MDN hydrogel has important application value in the fields of smart actuators,soft robots,electronic skin,and wearable flexible sensing devices.