Preparation And Properties Of Polypyrrole Modified Microwave Absorbing Composites

With the development of radar stealth technology and electronic communication technology,higher requirements are put forward for the performance of electromagnetic wave absorbing materials.Polypyrrole(PPy)is an important class of conductive polymers that has received widespread attention in the field of wave-absorbing materials because of its simple synthesis process,low density,good electrical conductivity and stable chemical properties.Therefore,the preparation of a kind of PPy-based composites with excellent electromagnetic absorption properties has important research significance and good development prospects.As a kind of conductive lossy wave absorbing material,this thesis focused on the design and preparation of three PPy-based composites,including zinc oxide(Zn O)/PPy composites with different morphologies,MWCNTs(rGO)/PPy binary composites and MWCNTs/rGO/PPy ternary composites.The effects of the structure and composition of these composites on their electromagnetic parameters and absorbing properties were explored,and the microwave loss mechanism was analyzed.The surface morphologies and crystal structure of the composites were analyzed by field emission scanning electron microscopy(FESEM),transmission electron microscopy(TEM),X-ray diffraction(XRD),Raman spectroscopy(Raman),X-ray photoelectron spectroscopy(XPS),and infrared spectroscopy(FTIR).The electromagnetic parameters of the composite materials were tested by vector network analyzer(VNA)and the microwave loss mechanism was analyzed.The details were as follows:(1)Hollow porous,flower-like and rod-like structured Zn O and corresponding three Zn O/PPy composites were successfully fabricated by hydrothermal and in situ polymerization methods.The modulation of the Zn O content wrapped on PPy was achieved by regulating the amount of pyrrole,which in turn modulated the dielectric properties of the Zn O/PPy composites.The results show that the hollow porous Zn O/PPy composite has the widest microwave absorption band and the best overall performance.The minimum reflection loss value of hollow porous Zn O/PPy composites is up to-48.5 d B with an effective absorption bandwidth of 6.1 GHz at a matched thickness of 2.2 mm at a pyrrole dosage of 0.8 m L.The flower-like Zn O/PPy composites with a minimum reflection loss value of-20.1 d B at 14.5 GHz and an effective absorption bandwidth of 6.6 GHz when the thickness is 1.6 mm.The rod-like Zn O/PPy composites has strong microwave absorption performance in the high frequency region,with a minimum reflection loss value of-59.7 d B at 15.8 GHz and an effective absorption bandwidth of 6.4 GHz at a thickness of2.7 mm.The introduction of the conductive polymer PPy and the hollow porous structure of Zn O can effectively improve the dielectric properties of the composites and form multiple reflections of the incident electromagnetic waves,while forming an interfacial polarization effect between PPy and Zn O,both of which are conducive to improving the microwave absorption properties of the composites.(2)The MWCNTs/PPy and rGO/PPy composites with homogeneous PPy coating were successfully fabricated by modification of PPy on MWCNTs and GO by in situ polymerization.The effect of the variation of PPy content on the microwave absorption properties of different carbon matrix composites was investigated.The results show that the appropriate amount of conducting polymer can effectively improve the microwave absorption performance of rGO/PPy composites.At a pyrrole dosage of 0.3 m L,the rGO/PPy complex achieves a minimum reflection loss value of-69.7 d B at 17.5 GHz with a thickness of 1.9 mm.The relaxation loss plays a key role in the microwave decay of rGO/PPy.When the amount of pyrrole in MWCNTs/PPy composites is too high,the PPy cladding layer formed is too thick,resulting in poor impedance matching,high reflection loss values of above-10 d B,as well as poor microwave absorption performance.(3)The MWCNTs/rGO/PPy ternary complexes were successfully fabricated by the modification of PPy with complexes of MWCNTs and rGO under hydrothermal conditions using in-situ polymerization.The effects of MWCNTs and rGO composite substrates and the content of modified PPy on the microwave absorption performance of this ternary complex were investigated.The results show that the electromagnetic wave attenuation ability of the complexes shows a trend of increasing first and then decreasing with the increase of PPy content.When the pyrrole dosage is 0.3 m L,the MWCNTs/rGO/PPy complex has a large reflection loss of-52.2 d B and-54.1 d B at7.5 GHz and 11.0 GHz,corresponding to an effective absorption bandwidth of 2.2 GHz and 3.6GHz at a thickness of 3.5 mm and 2.4 mm,respectively.The interfacial polarization between MWCNTs/rGO composite substrate and PPy as well as the multi-gap network structure formed by tubes and layers can effectively attenuate electromagnetic waves,thus improving the microwave absorption performance of the composites.