| Under the national goal of "Carbon peaking and Carbon neutral",solar thermal storage technology with phase change materials as the core can solve the problem of temporal and spatial mismatch between solar energy supply and demand,which is of great significance to promote solar energy storage and utilization.Among them,solid-liquid phase change materials are widely used in solar energy storage technology because of their high latent heat,low cost,and good biocompatibility.However,the problems of inherent liquid-phase leakage and low light absorption coefficient have restricted the development of solid-liquid phase change materials.As a novel two-dimensional lamellar material,MXene has excellent photothermal conversion capability,and the construction of a three-dimensional MXene skeleton can absorb and utilize sunlight more effectively.However,MXene-based porous materials are usually fragile in structure,and the composite materials with phase change materials are often not flexible and cannot fit closely with the surface of the controlled parts,which leads to many problems such as large interface gaps,high heat loss,and low photothermal conversion efficiency.Therefore,it is important to construct MXene based flexible phase change energy storage materials with efficient photothermal conversion and thermal energy storage through structural design to promote solar energy storage and utilization.To address the shortcomings of liquid phase leakage,lack of light absorption,and excessive rigidity of phase change materials,this project selects MXene as the light absorption medium,assembles water-soluble polymers with MXene in situ,and constructs porous MXene carriers with large effective pore capacity,good deformation resistance,and strong light absorption.Further,the porous MXene carrier is used to encapsulate the phase change material for efficient storage purposes and to suppress the liquid phase leakage of the phase change material;the elasticity of the porous MXene carrier and the crystallization/melt transition of the phase change material are combined to endow the phase change composite with flexible deformation and recovery function;the porous MXene carrier rapidly absorbs sunlight to endow the phase change composite with photothermal conversion and thermal energy storage performance,thus obtaining high encapsulation,high flexibility,and high photothermal conversion efficiency in one phase change composite.The main work of this paper is as follows.(1)To investigate the photothermal conversion capability of MXene,two-dimensional sheet layers of MXene were prepared by in situ generations of hydrofluoric acid etched precursors combined with mechanical peeling methods such as ultrasonic handshaking.MXene aqueous solution with a zeta potential of-39 m V has good dispersion and stability,indicating its good hydrophilicity and can be combined with water-soluble polymers.MXene film shows excellent light absorption and photothermal conversion ability in the whole visible range and can reach 60 ℃ after 30 s of simulated solar illumination,which can effectively convert light energy into heat energy.Therefore,MXene can be used as an excellent photo-thermal conversion filler to improve the light absorption ability of phase change materials.(2)To solve the problems of phase change materials such as easy leakage,high rigidity,and poor light absorption ability,MXene with excellent photo-thermal conversion ability was combined with waterborne polyurethane(WPU),and WPU@MXene aerogel with excellent elasticity was prepared by the freeze-drying method,and the WPU/MXene aerogel with a three-dimensional porous structure was then used as a support substrate to encapsulate polyethylene glycol(PEG)to produce a WPU@MXene/PEG flexible phase change composite with photo-response capability.The obtained WPU@MXene/PEG phase change composites have good shape maintenance(95%@70 °C)and high enthalpy of the phase change(154.6 J/g).The phase change composite has a high photothermal conversion efficiency(91.3%)due to the uniform distribution of MXene in the 3D network structure and its excellent light absorption ability.In addition,combined with the elasticity of WPU@MXene aerogel and the solid-liquid phase transition of PEG,the WPU@MXene/PEG phase change composites can achieve good photoluminescent shape memory and self-healing function.The composite can fully recover to its initial shape within 70 s under simulated solar illumination,and the composite can maintain the initial mechanical properties(82.9%)after self-healing by light.The preparation of this flexible phase change composite based on water-based polymer(WPU)and photothermal conversion filler(MXene)provides a new way the design high-performance multifunctional phase change composites,and also shows great potential in the field of efficient solar energy utilization.(3)To further solve the problem that phase change materials are difficult to achieve flexibility at temperatures lower than their phase change temperature and to give them more functionality,inorganic hydrated salt phase change material sodium decahydrate sulfate(SSD)was combined with polyacrylamide(PAM)hydrogel by simple photoinitiated free radical polymerization while introducing The PAM/SSD/MXene phase change hydrogel with good thermal storage capacity,mechanical properties,photothermal conversion properties and can be used in the field of human thermal management and sensing.The PAM/SSD/MXene phase change hydrogel has good tensile properties,excellent encapsulation(>98% shape maintenance),and a large latent heat value(178.4 J/g).The introduction of MXene gives the phase change hydrogel excellent photothermal conversion properties and combined with the good stretchability and cutability of the hydrogel itself,it can be used as a thermostatic body heat therapy dressing.In addition,the PAM/SSD/MXene phase change hydrogel is conductive and exhibits strain-sensitive characteristics,so it can be assembled as a strain sensor with high sensitivity,reproducibility,and good cycling stability.Based on the good mechanical properties and sensing capability of PAM/SSD/MXene phase change hydrogels,human motions such as joint flexion,breathing,and smiling can be detected,and PAM/SSD/MXene flexible phase change composites show their potential for multifunctional applications in the fields of photothermal conversion,human thermal management,and motion detection. |
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