Studies On Magnetic-Field-Induced Epoxy Resin/Graphite Nanosheets Ordered Composites And Their Anisotropic Properties

Graphite nanosheets (GNs), a new carbon nanofiller, 50 nm in thickness and 0.5-20 micrometer in diameter averagely, possess a high aspect ratio of diameter to thickness and much better in-plane conductivity compared to that in c-direction. It is understandable that the alignment of GNs in polymer will result in the composite with anisotropic properties, due to the anisotropy of GNs. In this study, for the first time, GNs have been aligned in an epoxy resin through the inducement of magnetic field. Compared with the shear-force inducement, by this method, the composites have a much higher degree of alignment which can be adjusted much easily.Herein, we have investigated the alignment of magnetically modified GNs in epoxy resin by subjecting the mixture to an external constant magnetic field before the system cured to form epoxy resin/GNs highly ordered composites, and special attentions were paid on their anisotropic properties.GNs obtained from sonicating the expanded graphite were modified chemically by depositing magnetite nanoparticles onto their surface through wet-chemical coprecipitation of ferric and ferrous ions with sodium hydroxide in the absence of nitrogen protection and surfactant, and were characterized using XRD and SEM. It was found that excellent magnetite-coated GNs can be obtained at 30 oC with 5:1 molar ratio of Fe2+ to Fe3+ in the air. The coated GNs are electrically conducting and ferromagnetic at room temperature.The modified GNs were dispersed in epoxy prepolymer, and then subjected to a magnetic field before the suspension solidified. Modified GNs were aligned with their 002 planes parallel to the field direction in epoxy matrix forming an ordered structure. We have successfully obtained 1-dimensionally ordered composite through single-directional inducement and 2-dimensionally ordered composite by double-directional inducement which were confirmed by XRD and AFM measurements. The 1-dimensional orientation of GNs brought about an improvement in transmittance of composite films in the visible light region of 400-750 nm in wavelength and an remarkable enhancement in the tensile strength in direction perpendicular to the magnetic filed. The two-dimensionally ordered composites with modified GNs being induced to align with layers parallel to each other display interesting anisotropic electromagnetic interference fielding shielding properties.