Preparation And Electrical Properties Of Graphene Loaded Fe₃O₄/Silicone Rubber Magnetic Field Induced Orientation Composites

The filler filled conductive silicone rubber composite is composed of conductive filler and silicone rubber matrix.How to effectively solve the dispersion and orientation of fillers in silicone rubber is an important research direction for the preparation of high-performance conductive silicone rubber materials.Although the orientation structure in the composite will reduce the contact between the fillers in the non-orientation direction,the percolation value will be further reduced in the orientation direction,so as to reduce the resistivity of the composite and further improve its electromagnetic shielding ability.In this paper,nano-Fe（OH）₃colloidal particles and graphene oxide sheet materials were electrostatic self-assembled,and then the excellent performance of flake Fe₃O₄supported graphene powder was prepared by inert gas reduction（Fe₃O₄@RGO）.Then,the composites were prepared by filling room temperature vulcanized liquid silicone rubber（SR）with Fe₃O₄@RGO filler.Fe₃O₄@RGO in the composites are oriented by static magnetic field,translational magnetic field and rotational magnetic field during normal temperature vulcanization.Furthermore,the relationship between these magnetic field（translational magnetic field and rotational magnetic field）and Fe₃O₄@RGO orientation and the influence on the structure and electrical properties of Fe₃O₄@RGO/SR composites are investigated.The main conclusions are as follows:（1）Oxidized groups on GO surface create good conditions for electrostatic adsorption of Fe₃O₄.After Fe₃O₄were loaded and reduced by inert gas at high temperature,most oxygen-containing groups on GO surface are reduced.After loading,the mass fraction of Fe₃O₄in Fe₃O₄@RGO is about 26.06%-28.58%,the saturation magnetic field intensity of Fe₃O₄@RGO composite powder is 25.65emu/g,and there is no obvious hysteresis phenomenon of Fe₃O₄@RGO powder.The seepage threshold of the Fe₃O₄@RGO powder in the Fe₃O₄@RGO/SR composites is 25wt%.（2）For Fe₃O₄@RGO/SR composites,when the dosage of curing accelerator was 4%,the Fe₃O₄@RGO/SR composites began to vulcanize after about 200s,and were basically vulcanized after 800s.The cyclohexane did not significantly improve the conductivity of composite materials,the amount of cyclohexane increased,the conductivity decreased.The Fe₃O₄@RGO cloud affected the vulcanization process of silicone rubber when the addition of Fe₃O₄@RGO reaches more than 35 wt%,but it had no obvious effect on the vulcanization process of the composites in the range of20wt%-30wt%,and Fe₃O₄@RGO has excellent thermal conductivity,the heat resistance of Fe₃O₄@RGO/SR composites improved.（3）For the addition of 25wt%Fe₃O₄@RGO,Fe₃O₄does not move obviously in the composites under a relatively weak static uniform magnetic field,while Fe₃O₄@RGO can be oriented along the magnetic field direction under a static magnetic field of 150m T.At the magnetic field intensity of 180m T,Fe₃O₄@RGO in the composite not only enriched onto the surface,but also effectively oriented and aligned along the direction parallel to the magnetic field.When the static magnetic field intensity varies from 30m T to 210 m T,the shielding band of Fe₃O₄@RGO/SR composites became wider,and the shielding performance is obviously enhanced.When the static uniform magnetic field intensity is 180m T,the shielding efficiency of the composite material reaches17.8d B.（4）After the addition of 25wt%Fe₃O₄@RGO and 180m T,Fe₃O₄@RGO can be effectively oriented along the magnetic field direction and distributed in continuous strips with the magnetic field moving in parallel with 2cm/s.When the magnetic field intensity reaches above 180m T,the sheet Fe₃O₄@RGO was more likely to move in the direction of magnetic field（enrichment）rather than orientation in the strong magnetic field,and this enrichment results in the decrease of electrical conductivity on the opposite side of the samples（lower surface of the sample）.The electromagnetic shielding efficiency of Fe₃O₄@RGO/SR composites was about 18d B,19d B,20d B and 21d B respectively under the translational magnetic field of 120m T,150m T,180m T and 210m T.（5）When 25wt%Fe₃O₄@RGO was added,the cross-section of the composites appeared undulating"wavy fringe"at the translative velocity of 2cm/s under the condition of 180m T.Fast motion speed is not conducive to the movement and orientation of Fe₃O₄@RGO.With the increase of translational magnetic field velocity,the surface resistance of Fe₃O₄@RGO/SR composite decreases,but the amplitude is not obvious.Correspondingly,when the translational magnetic field velocity changes from 2cm/s to 6cm/s,the shielding property of the composites gradually increases,but the shielding property gradually decreases when it changes from 6cm/s to 10cm/s.By comprehensive analysis,the translational velocity of 2-4cm/s is more favorable to the motion and orientation of Fe₃O₄@RGO in the composites.（6）With the addition of 25wt%Fe₃O₄@RGO and the increase of rotating magnetic field velocity at 180m T,obvious undulated"wavy"fracture fringe can be observed when the rotational speed is 2 r/s-6 r/s.This"wavy fringe"is the result of the periodic movement and orientation of Fe₃O₄@RGO under the condition of magnetic field movement.The speed is too fast,although the silicone rubber and Fe₃O₄@RGO can be effectively dispersed,but the phase structure is not continuous and unable to form a continuous network structure.（7）The magnetic field size and direction could change periodically,the sheet Fe₃O₄@RGO powder moved and oriented periodically,and then can be locally oriented.Finally,the silicon rubber and Fe₃O₄@RGO powder in the composites form a dual continuous network structure.At 2r/s,the frontal and reverse resistances of Fe₃O₄@RGO/SR composites are the smallest,which are 307±16Ωand 1917±112Ω,respectively.With the increase of magnetic rotation speeds,the surface resistances of Fe₃O₄@RGO/SR composites decreased,but the amplitude is not obvious.（8）The electromagnetic shielding property of pure silicone rubber is poor.Without any magnetic field orientation,the electromagnetic shielding efficiency is 12.69d B（33.64%reflection,66.36%absorption）for the composites with 25wt%Fe₃O₄@RGO.After the orientation of translational magnetic field and rotating magnetic field,the electromagnetic wave absorption is dominated by the structure of sheet Fe₃O₄@RGO which was a continuous chain shape along the orientation of magnetic field.After2cm/s,180m T translational magnetic field orientation,the electromagnetic shielding efficiency of the composites is 20.26d B（16.68%reflection,83.32%absorption）.At2r/s and 180m T,the electromagnetic shielding efficiency of the composite material is21.6d B（18.14%reflection,81.86%absorption）.