Fabrication And Performances Of Anisotropic And Nanocomposites Based On Bidirectional Freezing Assembly

High-performance nanomaterial is always limited by single structure,which could not meet the needs of practical applications.Assembling nanomaterials into three-dimensional(3D)assemblies with multi-scale is an important way to prepare high-performance nanocomposites.Due to highly ordered layered structure,biological tissues such as shells exhibit excellent mechanical properties.Inspired by this structure-property relationship,the anisotropic design of the material structure is an effective method to improve the material performance.Nowadays,researchers often use bi-directional freezing method to obtain anisotropic structures,which represents an effective e way to obtain 3D assemblies.In this dissertation,silver nanowires(AgNWs)and sodium alginate(SA)are combined to construct self-assembled materials with 3D ordered layered structure via a bidirectional freezing method.Furthermore,the self-assembled materials are used as scaffolds,and poly-N-isopropylacrylamide and epoxy resin are filled to construct the composites with application potential in the field of flexible sensors and engineering,respectively.The research contents are as follows:1.Based on bidirectional freezing method,used AgNWs and SA mixed solution as experimental systems,and the AgNWs-SA aerogel was obtained after freeze-drying.Four different microstructure aerogels were obtained by adjusting the concentration of AgNWs and SA in the mixed system.Due to the highly ordered layered structure,aerogels have excellent anisotropic properties.The conductivity of the obtained aerogel is as high as 110.6S/m,and the difference of conductivity in two directions can be up to 4 folds;and the difference of compressive stress between two directions is up to 5.8 folds at 30% compressive strain.Additionally,the prepared aerogel also exhibits anisotropy of photothermal effect.2.The obtained aerogels as scaffolds were further filled with poly-N-isopropylacrylamide to prepare anisotropic composite hydrogels.The stress loss of the composite hydrogel is only 7.5% after 500 compression cycle tests with 50% strain.And the difference of compressive stress in two directions can be up to 3 folds.The electromechanical properties tests illustrate that the resistance of the hydrogel varies with the change of compressive strain.When the compressive strain is 50%,the relative change rate of resistance can reach 55.1%.Furthermore,the prepared hydrogel can be designed to detect the direction of external force and changes in human joint movement through electrical signals,indicating its potential applications in the field of sensors.Moreover,epoxy resin is also filled into the AgNWs-SA scaffold,the prepared nanocomposite epoxy resin has a 33.3% higher fracture toughness than pure epoxy resin,and the conductivity of the nanocomposite epoxy resin is up to 110.5S/m.Meanwhile,it also has the advantages of stable conductivity in different humidity and temperature environment.The composite is expected to be used in the engineering field.