Preparation,Structure And High Efficiency Radiative Heat Management Of MXene-Based Infrared Low Emission Materials

Low infrared emissivity materials can significantly reduce the thermal radiation energy in the infrared band,which has important application value in infrared stealth,thermal camouflage,radiation heating and other fields,and has been widely concerned by researchers.Low emissivity materials are the key factor to realize low infrared radiation energy.Metal materials are typical low infrared emission materials,but they have some disadvantages such as high density,poor flexibility,difficult machining and easy corrosion.In addition,the intrinsic infrared emissivity of most metal materials is not low,and usually requires a complex polishing process to reduce the surface roughness,so as to obtain a relatively low infrared emissivity.At present,how to prepare high performance and easy to process low infrared emission materials is still a key problem to be solved urgently.At the same time,the increasingly complex and diversified use environment has put forward higher requirements on the functional characteristics of low infrared emissivity materials,such as photothermal,electric heating,radiation heating and mechanical properties.In order to solve the above problems,MXene based films,aerogel and composite foam with low infrared emission were constructed by vacuum assisted extraction and filtration and freeze drying with MXene as the matrix.Their intrinsic infrared emission and solar absorption rate were systematically studied,and the contribution of low infrared thermal radiation to photothermal/electrothermal conversion was discussed.And its thermal camouflage,solar heating,electric heating,radiation heating and mechanical properties were studied in depth,the main contents are as follows:（1）Ti₃C₂T_x MXene films with excellent radiant thermal camouflage,solar heating,electric heating and radiation heating properties were prepared by vacuum assisted filtration method.It is found that MXene film has very low infrared emissivity（14.5%）and excellent thermal camouflage performance,which can reduce the thermal radiation temperature of the target object at 300℃by 200℃in indoor environment.At the same time,the absorption rate of Ti₃C₂T_x MXene film in solar spectrum is up to 79.6%,which is higher than most materials.The low infrared emissivity of MXene film greatly reduces its radiant heat loss,giving it excellent photothermal/electrothermal conversion efficiency.Under the solar irradiation of 750 W/m²,the surface saturation temperature of MXene film can reach 84.3℃,which is 40℃higher than the ambient temperature.The true saturation temperature of MXene film can be rapidly increased to 201℃by applying 1.5 V driving voltage.Moreover,when the solar radiation is weak,the temperature of MXene film can be maintained to about 75℃by applying different external constant voltage.In addition,the MXene film shows excellent radiative heating performance,raising the temperature of artificial skin and real human skin by 7.0℃and 2.4℃,respectively,without consuming external energy.（2）A series of MXene films of different thickness with excellent thermal camouflage and solar heating performance were prepared by simple freeze-drying method,the porosity and density of MXene aerogel were controlled by applying pressure.MXene aerogel with different compression thickness showed well radiative thermal camouflage.In indoor environment,the radiative temperature of high temperature target object（～300℃）can be reduced by more than 180℃.During the compression process of MXene aerogel,the thermal camouflage mechanism evolved from heat insulation dominant to double contribution of heat insulation/low infrared emission,and then to low infrared emission dominant.This unique mechanism enables MXene aerogel to always show excellent thermal camouflage performance when deformed by external forces.At the same time,the low infrared emission MXene film is organically combined with the thermal insulation MXene aerogel,which can show a better radiant heat camouflage performance.In the indoor environment,the radiation temperature of the high temperature target object（～300℃）can be camouflaged to50℃.In addition,under solar irradiation of 600 W/m²,the saturation heating temperature of MXene aerogel with different compression thickness can reach 50-65℃.（3）Melamine/MXene composite foams with different MXene contents were prepared by freeze-drying method by introducing melamine as support,and their mechanical,thermal camouflage and solar heating properties were studied.The performance of melamine/MXene composite foams can be regulated by changing the concentration of MXene soaked solution.The compressive strength of melamine/MXene composite foam can reach 101.5 KPa under 90%compressive strain.At the same time,both the initial composite foam and the melamine/MXene foam after 100cycles of compression show excellent thermal camouflage,which can reduce the radiation temperature of～310℃objects by more than 150℃.In addition,the melamine/MXene composite foam showed excellent solar heating performance.Under the condition of low temperature（～10℃）and low solar irradiance（400 W/m²）,the temperature of the composite foam can be increased by more than 15℃.