| With the booming of 5G era,the increasing quantity of various kinds of intelligent wireless communication equipment leads to the increasingly serious electromagnetic pollution.High power electromagnetic radiation not only affects the normal operation of implanted medical equipment and precis industrial instruments but also does harm to human health by long time exposure.Therefore,the demand for electromagnetic interference shielding(EMI)materials which can effectively block the transmission of electromagnetic waves is rapid.In recent years,two-dimensional transition metal carbide(MXene)has been focused of researchers on EMI materials due to its high electrical conductivity,abundant surface functional groups and superior liquid processability.Among a variety of MXene-based EMI materials,three-dimensional(3D)MXene structure has advantages of being lightweight,porous and highly conductive,which has attracted extensive attention of researchers.However,due to the weak interlamellar interactions between the MXene nanosheets,the construction of 3D MXene usually requires the assistance of strong bonding materials,which will reduce the electrical conductivity of 3D MXene and affect its EMI performance.In order to solve this problem,MXene/PPy hybrid aerogel with high electrical conductivity was prepared by combined MXene with polypyrrole-an inherently conductive polymer.In addition,the appearance of the existing MXene 3D materials is limited by the preparation method or the molding mold,while 3D printing can flexibly control the shape and size of the printing structure to realize the continuous and large-scale preparation of 3D materials.Direct ink writing(DIW)has been proved to be an effective method to construct the 3D structure of MXene,but this forming method has strict requirements on the rheological properties of ink,so the preparation of printable MXene ink is the key element.Using the triblock polymer Pluronic F-127(PF-127)to adjust the rheological properties of the ink,a thermoresponsive ink suitable for printing was obtained,and MXene aerogels with controllable shape and adjustable shielding performance were prepared.The main research contents are as follows:(1)Preparation of highly conductive MXene/PPy hybrid aerogels by one-step method and their electromagnetic shielding properties:In order to ensure the electrical conductivity of the hybrid aerogel,the MXene/PPy hybrid 3D structure was obtained by in-situ polymerization of polypyrrole and one-step molding.First,the ethanol/water dispersion of MXene was added with pyrrole monomers,and some pyrrole monomers were anchored to the edges and defect sites of MXene through self-polymerization by intense stirring,thus improving the stability of MXene nanoplates.Then MXene/PPy hydrogels were obtained in one-step,with the initiator was added to polymerize the remaining pyrrole monomer and connect the MXene nanosheets.Finally,MXene/PPy hybrid aerogels were obtained by freeze-drying.MXene was used as the skeleton for hybrid aerogel,and PPy was coated on the surface of MXene and connected with MXene nanosheets to construct 3D aerogel with high electrical conductivity.When the content of MXene in the hybrid aerogel is only 20 wt%(the filler amount of paraffin composite material is 0.34 vol%),the electrical conductivity is up to 147 S m-1,and the EMI shielding efficiency is 44 dB.(2)Preparation of thermoresponsive MXene ink and customized electromagnetic interference shielding MXene aerogels:In order to obtain highly conductive 3D-printed MXene aerogels,thermoresponsive MXene/PF-127(MPF)composite ink was prepared by using PF-127 as a rheological modifier and taking advantage of its characteristics of low-temperature solution-gel phase transition.MPF ink was prepared by mixing the water-soluble polymer PF-127 with MXene slurry,the PF-127 phase was transformed by low-temperature printing(40℃),and the self-supported three-dimensional structure of MXene was prepared.Via controlling printing conditions,the EMI shielding performance of MPF aerogels can be flexibly adjusted between 32 dB and 57 dB.After annealing treatment,the PF-127,interlamellar bound water and some surface functional groups of MXene were partially removed,and the aerogels exhibited high conductivity(2030 S m-1)and excellent EMI shielding performance(71 dB,1.2 mm).Meanwhile,the aerogels have excellent joule heating performance and reach a saturation temperature of 100℃ at a low voltage of 1.2 V,which could be applied in the field of electric heating. |
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