Preparation And Shielding/Absorbing Performance Research Of Carbon Nanotube Based Composites

Under the background of the rapid development of electronic devices and electronic communication,which in turn brings about increasingly complex and serious electromagnetic pollution and information security,a series of studies on electromagnetic wave shielding and absorption materials have been extensively reported.Due to the advantages of low density,high electrical conductivity,high specific surface area and high stability,and the adjustable structures and morphologies（film,powder,fiber,aerogel）,the conductivity and electromagnetic parameters of carbon nanotubes can be easily adjusted through structural and morphological adjustments,thus having great advantages in the preparation of shielding and absorbing materials for different frequency regions.Therefore,this thesis is based on the lack of research on carbon nanotube-based shielding/absorbing materials preparation in different frequency and mechanism,on the basis of the material research idea of composition,structural morphology and performance relationship,as well as carbon nanotubes and their nano-hybrid structure with various structural morphology as the main research object,we prepare carbon nanotube-based electromagnetic materials for the medium frequency region and high frequency region through the composition,structural design while optimized shielding and absorbing performances are received,and disclose the transformation relationship between shielding and absorbing of carbon nanotube-based electromagnetic materials and their multi-functionalization properties,so as to deepen the understanding of the design of carbon nanotube-based shielding/absorbing materials and the transformation relationship between shielding and absorbing of material.Based on these,the works carried out in this paper are as follows:Firstly,carbon nanotubes with different macroscopic morphologies were prepared by different treatment processes:carbon nanotube film precursors were prepared by floating chemical vapor deposition,and then the precursors were treated with different solvents（ethanol/water,acetone/water,acetic acid/water,sulfuric acid/water in a volume ratio of 4:1）and rolling processes to obtain carbon nanotube films with different morphologies and structures,then the electrical conductivity,electromagnetic shielding properties,hydrophobicity,high temperature resistance and electrothermal properties of these carbon nanotube films were investigated.For the modification of carbon nanotube powder,the effect of oxidation time on microstructure and morphology was investigated via high-temperature air atmosphere oxidation treatment of pristine carbon nanotube powder,thus providing a certain material and theoretical basis for the following research on carbon nanotube-based shielding/wave-absorbing materials.Secondly,based on the above preparation method of carbon nanotube films,the prepared carbon nanotube films were laminated with carbon fiber reinforced epoxy prepreg under hot pressing conditions,and the number of laminated layers of carbon nanotube films/carbon fiber reinforced epoxy prepreg,the lamination angle and the surface density of carbon nanotube films were regulated to control the electromagnetic parameters of the materials（complex dielectric constant and complex magnetic permeability）affected by internal heterogeneous interfaces in the composite plate and conductivity,thus investigating their electromagnetic shielding and microwave absorption properties and analyzing the mechanism of the electromagnetic properties via the physical parameters.In addition,the high temperature resistance,acid-base resistance and hydrophobic properties of the prepared composite plates were evaluated by analytical methods such as thermal weight loss analysis to reveal the multifunctional applications of carbon nanotube film-based electromagnetic shielding/microwave absorption materials.In addition,to endow the CNT-based electromagnetic materials with obvious shielding-absorbing properties,the MWCNT powder,which is easier to change the addition amount and dispersion state,replace the locally distributed carbon nanotube film to tune the electrical conductivity and dielectric,and the structural defects were introduced into the MWCNT by the oxidation reaction according to the research method in Chapter 3,and the composite component molybdenum oxide was adjusted to a porous morphology with oxygen vacancy defects by regulating the hydrothermal reaction conditions to prepare a morphology-adjustable structure-defect-containing the Mo O_3-x@MWCNT porous nanohybrid structure with adjustable morphology（promote impedance matching）.Its electromagnetic shielding and microwave absorption properties in the frequency range of 1-18 GHz was studied by adjusting the content of the porous nanohybrid structure,and the principle that the electromagnetic material based on MWCNT powder has good shielding and absorbing properties in the high frequency region was analyzed according to the electromagnetic parameters and electrical properties.Meanwhile,the nanohybrid structure was compounded with PTFE emulsion under certain formulation conditions to obtain Mo O_3-x@MWCNT/Polytetrafluoroethylene composite films,and the multifunctional properties of the composite films in photothermal de-icing,antibacterial as well as flame retardant were investigated.Finally,in order to further prepare carbon nanotube-based composite suitable for lower frequency region such as the medium frequency region,the MWCNT powder and Mo O_3-x were replaced by SWCNT powder and Fe₃O₄ with higher conductivity,respectively,and the SWCNT surface was functionalized and then compounded with the Fe₃O₄ nano-cage prepared by a simple one-step hydrothermal reaction under ultrasonic-mechanical stirring.The SWCNT@Fe₃O₄ nanocage nanohybrid structure with different composite ratios was obtained to increase the heterogeneous interfaces and dipoles in the structure,and finally it was homogeneously dispersed in a polydimethylsiloxane matrix and cross-linked by heating to obtain the SWCNT@Fe₃O₄nanocage/polydimethylsiloxane shielding and absorbing composite film,and the electromagnetic shielding and absorbing properties of the composite film in the X-band of the medium frequency region were evaluated.The shielding and absorbing transition relationships of the carbon nanotube-based electromagnetic materials and their mechanisms were analyzed,and the multi-functional properties in photothermal,thermoelectric and self-healing fields were also investigated.