Preparation Of Modified Graphene/Polyimide Composite Films And Their Electromagnetic Wave Absorbing Properties

In order to improve electromagnetic absorbing properties of graphene-based polymer composites,modify the compatibility of graphene with polymer,different methods have been utilized to modify graphene oxide(GO).Then,composite films with polyimide(PI)as matrix has been prepared by in suit polymerization and phase-separation technique,the structure and electromagnetic absorbing properties have been investigated.Finally,composite films with strong absorption,light weight,and thin thickness was obtained.The main research contents were summarized as follows:Non-covalent modified GO/PI electromagnetic wave absorbing composite films have been prepared and characterized.GO has been non-covalent modified with surfactant octadecyltrimethyl ammonium bromide(STAB)to obtain STAB-GO,which acted as the absorbing agent evenly dispersed in polyimide(PI)resins by in suit polymerization,then STAB-GO/PI composite films with thickness of 0.2 mm have been prepared by phase separation process.The effect of STAB-GO content on electromagnetic absorbing properties of composite films was analyzed.The results showed that,after modification,lamella spacing of STAB-GO hasincreased.The maximum reflection loss of composite films reached-18 d B on the frequency of 18 GHz,and the effective absorption bandwidth(Reflection loss(RL)?-10 d B)reached 6.3 GHz(11.7~18GHz)when STAB-GO content was 1%.The effective absorption bandwidth of composite film reached 9.4GHz(8.6~18GHz)with the content of 0.8%.Graphene oxide-polyaniline(GO-PANI)/PI electromagnetic wave absorbing composite films have been prepared and characterized.GO-PANI nanocomposite has been prepared by in suit polymerization,then 0.2 mm GO-PANI/PI composite filmshave been prepared.The effect of GO-PANI contenton electromagnetic wave absorbing properties of composite films has been investigated,and the absorbing mechanism has been proposed.The results indicated that long fibrous PANI sparsely and irregularly adhered tographene nanosheets,the maximum reflection loss of composite films reached-28.2d B on the frequency of 9.6GHz,and the effective absorption bandwidth(RL?-10 d B)reached 5.2 GHz(11.7 ~ 18 GHz)when GO-PANI content was 8%,the electromagnetic wave absorbing performance has improved compared to STAB-GO/PI.Through dielectric loss of graphene with PANI to electromagnetic wave and electromagnetic wave multi-reflection loss within the material,electromagnetic wave absorbing performance of GO-PANI/PI composite has been increased.In order to improve electromagnetic wave absorbing properties of composite films further,covalent modification to GO has been carried out,then,composite films have been prepared and characterized.Through covalent modification(CC)to GO,CCGO has been obtained,and PANI has been aggregated in the surface layer of CCGO,then CCGO-PANI nanocomposite has been prepared.Finally,CCGO-PANI/PI composite films with thickness of 0.2 mmhave been prepared by in suit polymerization and phase separation process.The results showed that through covalent modification,PANI with the form of short acicularwas arranged in graphene nanosheets densely.The composite film had the maximum reflection loss – 44 d B at 7.7 GHz,and the effective absorption bandwidth reached6 GHz(4.9~10.9 GHz)when CCGO-PANI content was 8%.Compared to GO-PANI/PI,the maximum reflection loss and effective absorption bandwidth of CCGO-PANI/PI have been increased obviously,and the effective absorption spectrum changed to lower,electromagnetic absorbing performance has been improved significantly.Dielectric loss of graphene and PANI was mainly absorbing mechanism,and neat arrangement of PANI have played an important role to improve the dielectric loss of composite membranes and multiple reflection loss.In summary,with the modification of graphene gravimetric to varying degrees,and dispersion of the nanocomposites in PI substrate have been carried out evenly by using in situ polymerization.Electromagnetic wave absorbing composite films with strong absorption,wide bandwidth,light weight and thin thickness have been prepared successfully.In addition,composite films hadexcellent thermal stability and mechanical properties,provided the referencefor ideal absorbing composites.