Effects Of Boron Nitride Nanosheets Modified By Sliver Nanoparticles On Thermal,mechanical,and Electrical Properties Of Epoxy Nanocomposites

Miniaturization of power equipment and electronic devices coupled with high voltage electromagnetic environment demands superior thermal conductivity and electrical insulation strength in insulating materials.Epoxy are widely used as insulating materials for their excellent electrical insulation properties,but their low thermal conductivity reduces the lifetime and reliability of power equipment.To improve the thermal conductivity of polymers,many kinds of nanomaterials with high thermal conductivity have been added as fillers.However,conventional methods to synthesize polymer composites with high thermal conductivity often degrade their insulation strength or cause significant increase in dielectric properties.In order to obtain insulating materials with both high thermal conductivity and high insulation strength,molecular dynamics simulation was used to simulate the properties of epoxy nanocomposites(EP-Ag BN,EP-Cu BN)doped with boron nitride nanosheets(BNNSs)modified by nano-silver(Ag NPs)and copper(Ag NPs-BNNSs,Cu NPs-BNNSs).Based on the simulation results,EP-Ag BN was selected to be the experimental group.The epoxy nanocomposite with high thermal conductivity,high insulation strength,low dielectric constant,and low dielectric loss was obtained.Using the composite material doped with BNNSs(EP-BN)as a control,the effects of the nanomaterials prepared in this article on the thermal and electrical properties of epoxy resins were analyzed,and their application prospects in insulation in power systems was confirmed.In this paper,in order to select the suitable nanofillers,the epoxy nanocomposites models of pure epoxy and EP-BN,EP-Ag BN,EP-Cu BN with different content were built and the thermodynamic and electrical properties was simulated.The results show that the addition of BNNSs,Ag NPs-BNNSs,Cu NPs-BNNSs can effectively improve the thermal conductivity of epoxy,in which the Ag NPs-BNNSs is the strongest.All the three nanomaterials can increase the glass transition temperature of the epoxy by weakening its molecular segment motion ability.The addition of the three nanomaterials can increase the dielectric constant of the epoxy nanocomposite by enhancing its internal dipole movement ability,and reduce the free volume fraction at the same time,which helps to improve the dielectric breakdown strength.The simulation results of the interface properties of the epoxy nanocomposites show that both Ag NPs and BNNSs have a strong binding energy with the epoxy matrix.Due to the synergistic effects of BNNSs and Ag NPs,the interface effect area of Ag NPs-BNNSs in the nanocomposites is significantly larger than that of BNNSs and Ag NPs acting alone,which helps to improve the thermal stability and mechanical properties of the nanocomposite.Based on the analysis of the thermodynamic and electrical performance simulation results,Ag NPs-BNNSs was selected as the experimential nanomaterials,and the BNNSs was used as the control group.In this article,BNNSs were prepared by liquid-phase exfoliation of hexagonal boron nitride,Ag NPs-BNNSs were prepared by reduction method,and the two were separately mixed into epoxy resin to prepare nanocomposite EP-Ag BN and EP-BN with different nano-material content.The XRD,TEM,SEM,XPS and other detection methods were used to characterize the properties of nanomaterials and composite materials,which show that their basic structure and performance were good.Compared with pure epoxy,Ag NPs-BNNSs can significantly improve the thermal conductivity(the thermal conductivity is increased by 1086%with a nanofiller conten of 25vol%),which is more than twice that of EP-BN.The results of thermal weight loss curve shows that the two nanomaterials can both increase the initial decomposition temperature and the temperature corresponding to the maximum decomposition rate of the composite,thereby improving its thermal stability.The analysis of the dynamic thermomechanical properties of composite materials shows that both nanomaterials can help increase the storage modulus of epoxy resin,reduce mechanical losses,increase glass transition temperature,and reduce the activation energy required for glass transition.Both of them achieve the optimal value when the doping amount is 20 vol%,and further increase of the doping amount of nano-materials will reduce the homogeneity of the composite material.Compared with the simulation results,the measured values of the thermal conductivity,glass transition temperature and elastic modulus of epoxy nanocomposites are close to their simulated values,which proves the accuracy of the simulation and the experimental results.In order to verify the application prospect of EP-Ag BN in power systems,the basic electrical properties of nanocomposites are studied in this paper.By analying of the wide-band dielectric spectrum of epxoy nanocomposites,it was found that Ag NPs-BNNSs and BNNSs can increase their volume conductivity,dielectric constant,and dielectric loss,but there will not result in the surge of the three.The volume conductivity(10^-14?10^-7S/m),dielectric constant(below 5.5),and dielectric loss(below 0.02)are still low.At the same time,the increase in temperature will also result in the increase in permittivity and dielectric loss.Research on the thermal stimulus current of composite materials on composite materials shows that the addition of nanomaterials will lead to an increase in the amount of polarized charge of the nanocomposite,which will increase the dielectric loss,and will also shallow the depth of its deep traps,resulting in the increase of dielectric constant.The addition of two nanomaterials increased the AC breakdown field strength and creepage breakdown voltage of the nanocomposites.Because of BNNSs successfully separated Ag NPs and prevented them from forming conductive channel,but its breakdown field strength did not decreased with the introduction of conductor silver.The finite element simulation method was used to simulate the electro-thermal coupling process of the composite material under alternating electric field potential.The results shows that Ag NPs-BNNSs can effectively reduce the temperature rise of nanocomposites in the electromagenetic environment,which proves its application potential in power equipment.