Studies On Construction Of 3D Nanostructures Based On Mxene And Their Polymer Composites

In the military,electromagnetic interference can affect normal operation of the device,simultaneously,the device is exposed to the inconsistency of the infrared characteristics between the device and the background.Therefore,the electromagnetic shielding material also needs to have static and dynamic stealth functions to prevent the protected target from being identified by infrared detectors.Two-dimensional transition metal carbon/nitride(MXene)is an ideal electromagnetic shielding material due to its layered structure,abundant surface functional groups,and excellent electrical conductivity and processability.In addition,the three-dimensionally structured aerogel has static infrared stealth function as a thermal insulation material,and the dynamic infrared stealth can be obtained by exploiting the electrothermal properties of MXene.Unfortunately,the weakness of gelation capacity of MXene lead to the fact that the construction of 3D MXene usually requires the assistance of materials with strong bonding.In order to solve this problem,bacterial cellulose(BC)with a large aspect ratio is used to assist MXene to prepare three-dimensional MXene/BC aerogels by directional freezing.Besides,electromagnetic shielding materials also have good flexibility,in the basis of MXene/BC aerogel,we introduced high elasticity TPU network and then prepared the MXene/BC-TPU composite foam.The MXene/BC-TPU foam has flexibility,lightweight,wide strain range and high electromagnetic shielding performance.The main research contents are as follows:(1)Preparation and properties of multifunctional MXene/BC aerogel:In order to solve the weakness of gelation capacity of MXene lamella,BC,a gel material,is used to assist MXene assemble,and and MXene/BC aerogel was prepared by using directional freeze-drying method,which is light weight,high conductivity,electromagnetic shielding performance and low working voltage for infrared stealth.The composite aerogel has low density(0.002-0.02 g/cm~3)and high compression modulus(compression modulus up to 400 k Pa at 80%strain).MXene/BC aerogel has excellent electromagnetic shielding performance,high thermal insulation and infrared stealth performance due to its high electrical conductivity and unique directional porous structure.MXene/BC aerogel with a density of only 0.002 g/cm~3 have excellent electromagnetic shielding performance of 25 d B in X-band,also it can be up to 84 d B by density adjustment.In addition,the excellent electrical conductivity of MXene/BC aerogel endows it with high joule heating performance.MXene/BC aerogel with a density of0.008 g/cm~3 can reach the equilibrium temperature of 120℃at only 2V operating voltage(far below the safety voltage of human body),and it has good dynamic stealth function.Due to the porous structure and extremely low density,the MXene/BC aerogel has excellent heat insulation effect,which is significantly better than commercial polyurethane foam,so it has a good static stealth function.(2)Lightweight and flexible multifunctional MXene/BC-TPU electromagnetic shielding foam:polymer-based nanocomposites with flexible,lightweight,compressible,and stretchable properties can be used as ideal electromagnetic shielding materials.The infiltration of the 3D conductive network by the vacuum impregnation technique can reduce the damage of the3D structure.By introducing a highly elastic,flexible network of TPU through vacuum impregnation technology in the MXene/BC aerogel conductive network prepared in the first part of the work,we can get a lightweight(～0.22g/cm~3),wide strain range and high electromagnetic shielding performance MXene/BC-TPU foam.The high-strength conductive network prepared by BC assisted MXene,enabling the MXene/BC-TPU foam to achieve an efficient electromagnetic shielding performance(76 d B in X-band at a low content).The introduction of TPU enables the MXene/BC aerogel to have incomparable flexibility properties of aerogels,and the strain range can reach–80～270%.Therefore,the MXene/BC-TPU composite foam has a shielding effectiveness retention rate of about 87%after 5000 compression-release cycles with 50%strain,and the shielding effectiveness retention rate after 100stretch-release cycles with 10%strain is about 70%.The MXene/BC-TPU composite foam also has a stable resistance change under a wide strain range of–80～80%,so it can also detect human motion signals with a stable output signal.