Preparation And Microwave Absorption Performance Of Graphene Aerogels With Multiple Adjustable Microstructure

With the rapid digitization and progress of communication technological in modern society,the increasing electromagnetic pollution has created the surging demand for advanced microwave absorbing materials for both civil and military applications.Graphene aerogels are widely considered as promising candidates for efficient microwave absorbing materials due to their good electrical conductivity and low density.In this work,homogeneous graphene aerogel with open-cell structure(OCGA)was successfully prepared by self-assembly technique of graphene oxide and freeze-drying process.The microstructure and macroscopic distribution of graphene aerogels were designed by adjusting the emulsification parameters of the preparation process,and the effects of the aerogel structure on the dielectric properties and microwave absorption performance were discussed.The main research work of this topic is as follows:(1)Nanoscale carbon materials are prone to excessive stacking and agglomeration,leading to mismatched impedance,so the key to the microwave absorption performance of pure graphene aerogel lies in its preparation technology.For this reason,the lightweight graphene aerogel material was prepared by Pickering emulsion technique and freeze-drying method,which solved the problem of excessive stacking and agglomeration of graphene.(2)The multilevel regulation of the microstructure of graphene aerogel is achieved by adjusting the concentration of graphene oxide solution in the preparation of Pickering emulsion,the ratio of aqueous(graphene oxide solution)and oil phase(diphenyl ether)and the shear strength of the emulsion.and the effect of the microstructure of the graphene aerogel on the microwave absorbing performance is discussed.OCGA showed significantly enhanced microwave absorption property without any second phase,and the minimum value of reflection loss reached-51.22 d B,while the material density was only 4.81 mg/cm~3.(3)Beyond above traditional absorption mechanism,a more specific loss mechanism is shown in OCGAs.On the one hand,OCGA has a unique open-cell structure,resulting in frequent refraction and reflection of electromagnetic waves inside and outside the microsphere,which greatly increases the propagation path of electromagnetic waves and improves the microwave multiple reflection losses.On the other hand,the open cells form microscale spherical conductive structures and OCGA is regard as a huge network composed of open-hole microspheres connected in series,parallel and other hybrid connection methods,which can respond to electromagnetic waves to form a huge resistance-inductor-capacitive coupling circuit.When the microwave reaches the aerogel,a time-varying induced current is generated in the circuit,and the electromagnetic energy is eventually dissipated in the form of heat.(4)We designed gradient structure for OCGAs to improve the microwave absorbing performance further.The gradient distribution of microspheres in graphene aerogels was achieved by centrifugal the Pickering emulsion,and the effects of macroscopical distribution of graphene aerogels on microwave absorbing properties were discussed.OCGA with high absorption,wide frequency band,low density and thin thickness was successfully prepared.It achieved an ultra-low reflection loss of-62.58 d B at the matching thickness of 3.2 mm and ultra-low filling rate(0.53 wt%).At the same time,the effective absorption bandwidth of the material reached 8.55 GHz.Such excellent microwave absorption performance is at a champion level among graphene-based materials.