Design And Preparation Of Flexible MXene Composite Films And Research On Electromagnetic Interference Shielding Performance

With the increase of electronic devices,the risk of electromagnetic interference(EMI)has increased significantly,and it is urgently demanded to develop high performance EMI shielding materials.MXene(Ti₃C₂T_x)show great potential in the field of EMI shielding due to their unique layered structure,metal-like electrical conductivity,hydrophilic surface,and ease of processing.Nevertheless,there are still a series of problems in the practical application of Ti₃C₂T_x-based films,such as poor mechanical properties,limited oxidation endurance,and the large-scale preparation of Ti₃C₂T_x-based composite films remains multiple challenges.In this thesis,carboxymethylcellulose sodium(CMC)was added into Ti₃C₂T_xsuspension to formulate Ti₃C₂T_x/CMC casting solution.The viscosity of the Ti₃C₂T_x/CMC casting solution was increased due to the cross-linking of Ti₃C₂T_x and CMC.The Ti₃C₂T_x/CMC composite films were successfully prepared by casting the Ti₃C₂T_x/CMC solution onto a non-woven fabric(NWF)substrate.The flexible NWF was used as a substrate to provide excellent mechanical properties,and Ti₃C₂T_x/CMC as a functional layer can provide effective EMI shielding.Ti₃C₂T_x/CMC2.5 composite films with 2.5 wt%CMC exhibited the superior EMI shielding properties.Furthermore,the 2-Ti₃C₂T_x/CMC2.5 composite film prepared by using 200?m coater with a functional layer thickness of only 1.8?m achieved an EMI shielding of39.3 d B,which met the commercial standards(20 d B).In addition,as the Ti₃C₂T_x/CMC2.5 composite films were based on a cheap non-woven fabric,it largely reduced the preparation costs while offering excellent mechanical properties with a large scale.In the folding endurance test of Ti₃C₂T_x/CMC2.5 composite films,the 2-Ti₃C₂T_x/CMC2.5 functional layer showed obvious cracks after 123 folds,indicating that the adhesion between the functional layer and the substrate was poor,resulting in the limitation of the practical application of Ti₃C₂T_x/CMC2.5 composite films in EMI shielding.Base on the above research,Ti₃C₂T_x/CMC2.5-PHA and Ti₃C₂T_x/CMC2.5-TPU films with sandwich structure by casting a flexible polymer protective layer on Ti₃C₂T_x/CMC2.5 composite films were prepared with characterization and comparison of their morphological structures.Ti₃C₂T_x/CMC2.5 films displayed the best EMI shielding efficiency at the similar functional layer thicknesses.The Ti₃C₂T_x/CMC2.5-PHA films were close to the Ti₃C₂T_x/CMC2.5 films in terms of EMI shielding,while the EMI shielding efficiency of the Ti₃C₂T_x/CMC2.5-TPU films was reduced,which still met the commercial standards.In terms of folding endurance,the Ti₃C₂T_x/CMC2.5-TPU films showed outstanding folding endurance with only minor cracks after more than 65,000 folds due to the excellent mechanical properties of NWF and the excellent flexibility of the TPU protective layer.The EMI shielding mechanism,mechanical properties and durability of the Ti₃C₂T_x/CMC2.5-TPU films were further investigated.The existence of hydrogen bonds between the Ti₃C₂T_x/CMC2.5 functional layer and the TPU protective layer was demonstrated.The presence of hydrogen bonding can efficiently enhance the adhesion between TPU and Ti₃C₂T_x/CMC2.5 functional layer.The SE_A and SE_Rvalues of the Ti₃C₂T_x/CMC2.5-TPU films were calculated.It was found that the SE_Avalues were higher than the SE_R values,indicating that the EMI shielding of the composite films were absorption.The SSE value of the 2-Ti₃C₂T_x/CMC2.5-TPU film(123333 d B/cm)was calculated.Compared with previous literature,it was found that the performance of 2-Ti₃C₂T_x/CMC2.5 was much higher than the majority of the reported results.Further investigation into the stress and strain of the Ti₃C₂T_x/CMC2.5-TPU films revealed that the Ti₃C₂T_x nanoflakes enhanced the mechanical properties of the NWF substrate.By comparing the oxidation endurance of the 2-Ti₃C₂T_x/CMC2.5 film with 2-Ti₃C₂T_x/CMC2.5-TPU film,the water resistance of the TPU protective layer and the protection of the Ti₃C₂T_x/CMC2.5functional layer were confirmed.