Preparation Of Multilayer Graphene With Deep Eutectic Solvent And Its Application In Thermally Conductive Silicone Rubber

The special two-dimensional atomic structure of graphene gives it ultra-high thermal conductivity,so graphene can be used as thermal conductive filler to improve the thermal conductivity of silicone rubber.However,there are two serious problems that restrict the application of graphene in thermally conductive silicone rubber:one is how to prepare graphene at low cost and scalability;the other is how to greatly improve the thermal conductivity of silicone rubber under low filler loading.In response to the above problems,the following experimental research was carried out:The deep eutectic solvent composed of choline chloride and urea was used to assist in ball-milling of expanded graphite,so that multilayer graphene（MG）was prepared at low cost and scalability.The experimental results showed that the prepared MG could be stably dispersed in DMF,and the absorption coefficient of MG in DMF was 824 L·g^-1·m^-1.MG had a thickness of about 11-12 layers,a lateral dimension of 2-5μm,a low degree of oxidation（mass ratio of oxygen to carbon was 0.10）,a low degree of sheet defects（I_D/I_G was 0.08）,and good thermal stability.Boron nitride-multilayer graphene hybrid filler（BN-MG）with a mass ratio of 1:10 was prepared by electrostatic self-assembly method,and BN-MG filled thermally conductive silicone rubber（BN-MG/SR）was prepared by solution mixing method.The results showed that the thermal conductivity of BN-MG/SR was not significantly lower than that of MG/SR with the same filler loading,and the specific gravity was not obviously increased,while the volume resistivity was three to four orders of magnitude higher,and the thermal stability of BN-MG/SR was good.When the filler loading was 3 wt%,the volume resistivity of MG/SR(6×10¹⁰Ω·cm)did not meet the electrical insulation requirements of electronic packaging,while the volume resistivity of BN-MG/SR was maintained at 2×10¹⁴Ω·cm.Magnetically functionalized multilayer graphene（Fe₃O₄@MG）with different coating mass ratios（1:2,1:1,3:1）was prepared by electrostatic self-assembly method,and vertically aligned Fe₃O₄@MG/silicone rubber composites（V-Fe₃O₄@MG/SR）were prepared by applying external magnetic field to align Fe₃O₄@MG along the direction of magnetic field.The obtained results showed that under the same MG loading（≤5wt%）,the thermal conductivity of randomly oriented Fe₃O₄@MG/silicone rubber composites（R-Fe₃O₄@MG/SR）gradually decreased and that of V-Fe₃O₄@MG/SR increased with the increase of coating mass ratio of Fe₃O₄@MG.Especially when the coating mass ratio of Fe₃O₄@MG was 3:1 and the MG loading was 5 wt%,V-Fe₃O₄@MG/SR exhibited a superior thermal conductivity of 0.64 W/（m·K）,which was 191%higher than that of R-Fe₃O₄@MG/SR,39%higher than that of randomly dispersed multilayer graphene silicone rubber composites（MG/SR）,and 433%higher than that of pure silicone rubber（0.12W/（m·K））.This phenomenon was explained by SEM and XRD tests of V-Fe₃O₄@MG/SR:Fe₃O₄@MG was induced to form chain-like bundles in silicone rubber matrix under the applied magnetic field,which enhanced the MG-MG interaction,and formed effective thermal pathways in the alignment direction,thereby improving the thermal conductivity of V-Fe₃O₄@MG/SR.