Preparation And Microwave Absorption Property Of Graphene/Electromagnetic Functionalized Organic Spheres Lightweight Absorber

The development of electronic technology and the widespread use of electronic equipment have brought convenience to our society and also built up an increasing complex electromagnetic environment,which has resulted in growing serious electromagnetic pollution problems.Microwave absorbing materials can effectively attenuate these harmful electromagnetic energy to ensure electronic equipment under normal operation without interference.Especially in military field,microwave absorbers have the ability to reduce the probability of the detection of military equipment and improve the survivability in battlefield.However,it's difficult to meet the demand of advanced stealth fighters or warships with thin thickness,light weight,strong absorption capacity and wide absorption bandwidth for conventional absorbers because of their large density and narrow bandwidth.In this paper,thermosensitive organic microspheres were used as templates to obtain electromagnetic functionalized spheres modified by magnetic or conductive materials,which could be used as lightweight microwave absorbers.Incorporating with conductive reduced graphen oxide?RGO?sheets in epoxy resin,an enhanced conductive network was formed with increasing conductive loss.Besides,RGO sheets with large specific surface area could be modified with magnetic nanoparticles.Composites with controllable electromagnetic parameters could be prepared with reasonable ratio of magnetic loss materials and dielectric loss materials,leading to improved impedance matching condition and realizing the requirements of broadband and strong absorption.The main contents are as follows:?1?The single-layer magnetic PANS@CoFe₂O₄ spheres with a layer thickness of about 1.5²?m were synthesized by co-precipitation method.The M_s and density was 44.7 emu/g and 0.053 g/cm₃,respectively.Combined with RGO sheets dispersed in epoxy resin,RGO-PANS@CoFe₂O₄ composites were prepared with stronger microwave absorption performance than pure RGO/EP and CoFe₂O₄/EP composites due to the incorporation of dielectric RGO and magnetic PANS@CoFe₂O₄ with improved impedance match.The minimum reflection loss was about-14.8 dB and the corresponding bandwidth was 3.6 GHz?12¹5.6 GHz?with a light density of0.41⁰.50 g/cm³.?2?The single-layer dielectric PANS@Ag spheres with a light density of 0.012g/cm³ were synthesized by silver mirror reaction.A developed conductive network was formed with the use of RGO sheets and PANS@Ag spheres,resulting in improved dielectric properties.Multiple reflection occurred as the incident EM wave propagated among the conductive RGO sheet and PANS@Ag network with increasing attenuation of EM energy.At the same time,the interfaces between conductive microsphere,RGO layer and resin also caused polarization relaxation.RGO-PANS@Ag composite showed a minimum reflection loss value of 28.1 dB at8.8 GHz and the effective absorption band was about 2 GHz with a density of0.49⁰.87 g/cm³.?3?The surface modification of the thermosensitive microsphere were conducted by coupling agent so that Fe₅₀Ni₅₀0 nanoparticles could be anchored on the surfaces to form a uniform shell with a thickness of 70¹40 nm.The density and M_s of as-prepared PANS@Fe₅₀Ni₅₀0 was 0.031 g/cm³ and 47.5 emu/g,respectively.The synergistic effect of dielectric RGO and magnetic PANS@Fe₅₀Ni₅₀0 gave rise to the enhanced absorption performance of RGO-PANS@Fe₅₀Ni₅₀0 composites.As the dosage of RGO and PANS@Fe₅₀Ni₅₀0 was both 1 wt%,the maximum absorption value was-16.1 dB at 12.2 GHz with an effective absorption bandwidth of 4.5GHz,and the density was about 0.73⁰.79 g/cm³.While the content of PANS@Fe₅₀Ni₅₀0 increased to 5 wt%,the absorption performance decreased to-11.1 dB with a lighter density of0.25⁰.34 g/cm³,which provided an effective method for the preparation of new light absorbing materials.?4?A two-step method of chemical reduction method and in situ polymerization was adopted to prepare double-layer PANS@PANI@Ag conductive microspheres with a density of about 0.018 g/cm³.The conductive polyaniline formed a dense network structure on the surface of microspheres,supplying more stable growth points for Ag nanoparticles.The thickness of PANI/Ag coating was about 500 nm.RGO and PANS@PANI@Ag microspheres in resin matrix made up developed conductive network structure,which could cause conductive loss,multiple scattering and reflection.In addition,interfacial polarization relaxation,defects polarization and electronic polarization also appeared and enhanced the dielectric loss.When the dosage of RGO and PANI@Ag was both 1 wt%,the RGO-PANS@PANI@Ag composites exhibited the strongest absorption capacity of-44.9 dB with a density of0.86⁰.91 g/cm³.With the increase content of conductive PANS@PANI@Ag,absorbing performance,the absorption capacity decreased due to wave reflection of the eddy current caused by alternating electromagnetic.As it increased to 5 wt%,the corresponding absorption peak decreased to 14.7 dB with a lighter density of0.47⁰.53 g/cm³.?5?A two-step method was used to produce lightweight double-layer electromagnetic PANS@Fe₅₀Ni₅₀@PPy microspheres,the M_s and density was about7.4 emu/g and 0.028 g/cm³ respectively.Coupling them with Fe@Ni-modified RGO sheets in epoxy,RGO/Fe@Ni-PANS@Fe₅₀Ni₅₀@PPy composites were prepared.The introduction of Fe@Ni endowed RGO magnetic property,effectively improving impedance matching condition and preventing the agglomeration of RGO.For RGO/Fe@Ni/EP composites,it displayed the minimum reflection loss of-22.7 dB at14.9 GHz with an effective absorption bandwidth of 5.5 GHz?12.5¹8 GHz?,which was one kind of strong and broadband absorbers While only 1 wt%PANS@Fe₅₀Ni₅₀@PPy was added,further enhanced conductive network was formed and it showed a minimum reflection loss of-17.8 dB dB at 15.3 GHz with an effective absorption bandwidth of 5 GHz.The addition of double-layer PANS@Fe₅₀Ni₅₀@PPy microspheres could reduce the density significantly from 1.24g/cm³ to 0.98 g/cm³ and retain an ideal absorption ability simultaneously.The comprehensive performance of broad absorption bandwidth,light weight and strong absorption capacity made it a promising candidate among these five as-prepared microwave absorbers.