Design And Performance Study Of Polyvinyl Alcohol/MXene-based Flexible Composite Phase Change Energy Storage Material

In the application process of organic composite phase change materials,there are usually problems such as low light-to-heat conversion efficiency,poor thermal conductivity and poor mechanical properties.Therefore,this paper designed PVA/MXene flexible composite phase change thin films with different morphologies and enhanced photothermal,thermal,heat storage and mechanical properties.The effect of the content of MXene and paraffin on the properties of PCM was investigated,and the internal relationship between the structure and properties of PCM was elucidated.A simple physical blending method was used to prepare paraffin/polyvinyl alcohol/MXene flexible composite phase change films with cross-linked structures.The positive effects of MXene on improving the mechanical strength,light-to-heat conversion,heat transfer and storage of the flexible composite phase change films were analyzed,and the synergistic enhancement mechanism of performance was explained.The results showed that the tensile strength of the flexible composite phase change films was 2.51 MPa,the thermal conductivity was 0.62 W·m^-1K^-1,and the latent heat was 99.27 J/g.And it had excellent light-to-heat conversion efficiency and light-driven shape recovery performance（nearly 100%）.The improved flexibility was mainly attributed to the fact that MXene nanosheets had rich surface functional groups,which provided additional hydrogen bond binding sites,thus facilitating cross-linking.Meanwhile,MXene was a light-to-heat conversion material,which effectively improved the light-to-heat conversion ability and heat transfer rate of the flexible composite phase change films.The effects of PW content on the morphology structure,thermal storage performance and tensile strength of paraffin/polyvinyl alcohol/MXene flexible composite phase change films were explored.The results showed that the content of PW did not significantly affect the morphology and structure of the flexible composite phase change films.With the increase of PW content,the actual latent heat of phase transition of the flexible composite phase change films increased regularly（45.81 J/g<117.02 J/g）.Moreover,the difference between the actual latent heat and the theoretical latent heat was about 7.1%.The mechanical properties of the flexible composite phase change films decreased regularly with the increase of PW content（2.95 MPa>1.01 MPa）.In addition,the flexible composite phase change films demonstrated excellent temperature regulation capability,which was beneficial for thermal management applications,but the thermal reliability may might to be further improved.The eicosane/polyvinyl alcohol/MXene flexible composite phase change materials with sandwich structure were prepared.Through the thermal stability analysis of the composite with similar loading of phase change medium and MXene,the results showed that the special sandwich structure effectively improved the leakage problem and the thermal reliability after phase change cycle.Moreover,the experimental results showed that the sandwich structure flexible PCMs had higher thermal storage capacity（157.43J/g）,higher mechanical properties（16.65MPa）and excellent light-to-heat conversion performance,which were higher than the cross-linked structures flexible PCMs.In this paper,flexible composite phase change materials with different structures were designed to solve the problems of large rigidity,easy fracture（or broken）and poor light-to-heat conversion ability of composite materials prepared by traditional packaging methods.It could meet the requirements of flexible installation,and reduce the interface contact thermal resistance,and improve energy utilization.It provides a new design idea for the practical application and environmental adaptability of flexible composite phase change material films.