Structure Design And Electromagnetic Shielding Performance Of Graphene Fibres And Their Composites

The high-frequency electromagnetic waves such as the microwave and radiofrequency waves are all around us,owing to the rapid development and rapid rise in usage of electronic devices.Developing light-weight and cost-effective shielding materials are,therefore,imperative to mitigate electromagnetic interference pollution caused by the intruding waves.Among others,graphene as a new type of carbon material circumvents the shortcomings of high density and easy corrosion of materials like metals for its advantages of low density,superior thermal stability,strong corrosion resistance,high conductivity and remarkable flexibility.Graphene fibers,a star member of graphene family,have been widely exploited in the fields of energy storage and sensors in the past ten years.However,there are few reports on their application in electromagnetic interference shielding.Therefore,in order to capitalize on the advantages of graphene fibers and optimally configure them in a composite material,we start from the study of the preparation and performance of graphene fibers,and then choose silicone rubber as the matrix to prepare a series of graphene fibers/silicon rubber composite materials and explore their electromagnetic properties as well as the structure-property relationships.The main research output in this article lies threefold as below:(1)Preparation and performance of graphene fibers:Firstly,we used a"one-step"method to quickly prepare single-layer graphene oxide,and then used its high concentration solution(40mg/ml)as a raw material to prepare graphene oxide fibers by wet spinning.After that,a series of fibers were prepared by means of methods,such as hydroiodic acid chemical reduction,microwave hydrothermal reduction,thermal annealing and electroplating.For intrinsic conductive fibers,the fibers obtained after two steps of reduction(chemical and thermal annealing at 600?)reached a conductivity of 605S/cm due to the nucleophilic substitution reaction of hydroiodic acid and the effect of high temperature.Compared to graphene fibers that were only chemically reduced,the conductivity had increased by 70%,and there was almost no weight loss before 600?.After treatment with nickel plating for 5 minutes,the fibers'electrical conductivity proved to be increased by more than 150 times to 5.5×10~4S/cm under the action of a 4?m thick Ni layer on the surface.(2)Structural design and electromagnetic shielding performance of graphene fiber composite materials:Taking advantage of the ease of fiber arrangement,a series of graphene fibers/silicon rubber binary composites were prepared through the adjustment of fiber spacing,quantity and design of sandwich structure and their electromagnetic shielding performance in the X-band were studied.The results showed that intrinsic conductive fiber composites were absorption-dominated shields due to the dielectric loss characteristics of graphene fibers.Featured with the exhibited Lorentz-type resonance,all samples showed frequency-selective properties.Following the design of the sandwich structure,the Fabry–Pérot cavity resonance acts to the case of the filling amount of mere 0.2wt%,the shielding effectiveness of the best intrinsic conductive fiber composites were increased by 41%(38 dB)as compared with the single layer samples of the same filler loading.Nickel plating fiber composites were improved by43%(63 dB)under the same condition,and accordingly,they transformed from reflection-dominant to absorption-dominant shielding materials.(3)A case study of hybrid fiber composites design and its electromagnetic shielding properties:Drawing on the synergy between ferromagnetic microwires and graphene fibers,we combined the two fibers to prepare microwires/graphene fibers/silicone rubber ternary composites.The electromagnetic shielding test revealed that,owing to impedance match of the dielectric loss and magnetic loss of microwires and the dielectric loss of graphene fibers,an"absorption-reflection-reabsorption"mechanism is believed to play important role,and that the ternary composites showed a synergistic effect in terms of its EMI performance.When the filler loading was only 0.059wt%,the shielding effectiveness of the composites reached 18 dB,which meant an attenuation of 98.4%electromagnetic wave.To sum up,the preparation methods were optimized to adjust the properties of the fibers;a series of electromagnetic functional composites with silicone rubber as matrix and single or hybrid fibers as fillers were obtained by controlling the arrangement of the fibers,and their electromagnetic shielding performance were systematically and deeply studied.The above results show that composites containing either single-type of filler,i.e.,graphene fiber or hybrid fibers can achieve efficient and selective shielding of incident electromagnetic waves under marked low loading through the manipulation of fiber arrangement.Graphene fibers composites also exhibit high degree of design freedom and fully adjustable performance.The present research on the structure-effect relationship between the structure of the fibers,which are the basic functional unit,the arrangement of the fibers and the electromagnetic performance of the overall composites provides an important scientific basis for the design and realization of light-weight and frequency-adjustable electromagnetic shielding composites built on graphene fiber;the advanced composites prove to be potentially valuable in practical engineering applications.