Preparation Of Conductive Coatings Based On Graphite Nanosheets And Its Electromagnetic Shielding Property

Carbonic series compound coatings were attracted by people due to their low cost, lightweight, anti-corrosion, simple technics and good applicability. They are important electromagnetic shielding (EMS) materials. In this paper, conductive compound coating based on graphite nanosheets (GNs) were prepared by blend method. The influences on conductivity and EMS performance of the compound coating were studied, on the base, EMS mechanism of it was proposed. The further research of GNs-based compound coating was also discussed in the end.The results of the study on conductivity for the GNs-based compound coating manifested: shape and diameter of the filler, content of the filler, pre-treatment of the filler, dispersion process, matrix resin, solvent, thickness of the coating and coating process were important in the functions. The smaller the diameter of the filler and the higher aspect ratio of GNs were, the better conductivity of the coatings showed. Conductivity was closely dependant on the GNs loading, the surface resistivity sharply decreased as GNs added at the beginning and achieved a relatively ideal value around 30 wt%, the resistivity continued to decline with more GNs were added but the coating surface situation and wearability were quickly decreased meanwhile. It was necessary to pre-treat GNs, especially using dodecyl trimethyl ammonium chloride to modify the surface of GNs, which effectively improved dispersion of GNs in the matrix and increased conductivity of the coating as well. The best dispersion process in this paper was sonication with the aid of shear mixing. Matrix influenced a lot on the conductivity, and acrylic resin showed better match with GNs. Solvent possessed strong solvency was benefit for GNs dispersion in the matrix, while good dispersion would improve the conductivity of the system. Conductivity was closed related with thickness. When d≤80μm (d is the thickness of the coating), the surface resistivity was high and decreased quickly. When d > 80μm, the surface resistivity decreased slowly and achieved a relatively low value with d = 400μm. In the end, it was found that coating process influence little on conductivity of the coating but influence a lot on its surface situation.The results of the study on EMS performance for the GNs-based compound coating manifested: conductivity, morphology of graphite, enamel-covering and sandwich-type structure design were important in the functions. The shielding effectiveness (SE) and conductivity of the coating varied uniformly, the better conductivity was, the higher SE performed. Therefore, the influences on conductivity affect EMS performance similarly. Using GNs as filler which possessed special nano-structure could increase the SE of the coating as compared with expanded graphite (EG). Covering enamel would decrease the SE of the coating. Furthermore, it was found that the SE of the coating was increased via structure design and sandwich-type coating showed better SE than ordinary coating in the paper. Based on the research above, we proposed the mechanism of GNs/resin coatings at the range from 300 KHz to 1.5 GHz was: the main shielding mechanism of the system was reflection and the secondary shielding mechanism was multiple reflections, while absorption can be neglected.