| Considering the rapid development of electronic communication technology,electromagnetic wave pollution becomes more and more serious.Therefore,the research of high-performance electromagnetic shielding(EMI)materials has received unprecedented attention.Ferromagnetic materials with high permeability are prone to create magnetic losses and are often used as the shielding materials in the low frequency range.While metals with good electrical conductivity are suitable for shielding in the low and high frequency of electromagnetic fields and electrostatic fields,however,it is difficult for the metals to meet the increasing practical application requirements due to their high density and the susceptibility to corrasion.In order to prepare new types of electromagnetic shielding materials with high shielding efficiency,light weight and good flexibility,we took GO as the construction unit to design and prepare porous films with quantities of cellular structures.The results indicate that the graphene film with porous structure shows obvious advantages:(1)lower cost;(2)low density;(3)high electromagnetic shielding efficiency,and help to realize the lightweight and electromagnetic shielding functionalization of graphene film materials.The main research contents are listed as follows:1.Porous graphene films were prepared by high temperature reduction method.First,we used the vacuum-filtering method to induce the self-assembly of GO and obtained the GO film because of the ordered stacking of GO sheets,and then the product is treated at 2800? to transform into the self-supporting graphene porous film with low density(?54 mg cm-3),high conductivity(?2.4×104 S m-1),high shielding efficiency(?190 ?m,98 dB),high specific shielding(1815 dB cm3 g-1)and a certain strength of 5.1 MPa.In addition to the comparison of graphene films obtained by the chemical reduction method and the high temperature reduction method about their differences on the structure and properties,we systematically explored the relationship between the thickness as well as the introduced porous structure and the shielding properties of graphene porous film.2.The multiscale porous structure of graphene films was controlled by template method.We prepared the graphene film with a multiscale pore structure using PS mierospheres as a template,and further explored the relationship between multistage pore structures and shielding performances.In detail,we prepared PS microspheres with different particle sizes by dispersion polymerization method,blended them with GO solution,and vacuum-filtered the mixture to form a film.For the removal of the template PS microspheres,we performed the low temperature pretreatment followed by the high temperature graphitization to prepare graphene film with hierarchical pores,during which the defects on graphene could be repaired,and the two-staged strategy effectively helped to maintain the multiscale pore morphology of the precursor.The particle size and content of PS microspheres have a significant effect on cell structure and material properties;the shielding performance is optimal(?260 ?m,97 dB)when the particle size of PS microsphere is 720 nm and the content is 30 wt%inside the precursor composite,in particular,the shielding performance is as high as 101dB at 12.3 GHz,and at this time the density of the porous graphene film as the final product is as lower as?71 mg cm-3.This works has important reference significance for realizing lightweight and high performance shielding materials through regulating structures. |
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