Construction Of Functionalized Porous Electromagnetic Wave Absorbing Materials By Pickering Emulsion Method And Research On Their Performance

In recent years,the rapid development of communication equipment has resulted in serious electromagnetic pollution,and it is an urgent necessary to develop efficient electromagnetic wave absorbing materials.In this paper,the Pickering emulsion technology stabilized by a variety of nanoparticles with the assistance of cellulose nanofibers(CNF)was utilized to construct a three-dimensional conductive porous electromagnetic wave absorbing material combined with freeze-drying,in-situ polymerization or high-temperature annealing processes.The synergistic effect of conductive nanoparticles and magnetic nanoparticles was studied on the electromagnetic wave absorption performance of the materials,and the electromagnetic wave absorption mechanism was further revealled.The specific contents are as follows:(1)Followed by the formation of the Pickering emulsion gel stabilized by CNF and carbon nanotube(CNT)in which the 1,2-dichloroethane solution of polylactic acid and Fe₃O₄nanoparticles acted as the oil phase,the CNF/CNT/PLA/Fe₃O₄electromagnetic wave absorbing materials were obtained through the further freeze-drying process.The effects of mass ratio of CNT to CNF in water phase and Fe₃O₄ concentration in oil phase on the morphology of Pickering emulsion droplets as well as the structure,morphology and performance of the resultant electromagnetic wave absorbing porous materials were studied.The results showed the final material had excellent electromagnetic wave absorption property with the reflection loss value of–65.14 d B at the thickness of 3 mm,resulted from that the conductive CNT and the magnetic Fe₃O₄ in the electromagnetic wave absorbing material not only provide conductive loss and magnetic loss,but also effectively improve impedance matching.In addition,it also exhibited good light-to-heat conversion,excellent heat insulation property and infrared stealth function.(2)The CNF/Fe₃O₄/PW composite foams were first prepared by freeze-drying the Pickering emulsion gel stabilized by CNF and Fe₃O₄ nanoparticles in which the1,2-dichloroethane solution of paraffin(PW)acted as the oil phase,and then the CNF/Fe₃O₄/PW/polypyrrole(PPy)foams for the electromagnetic wave absorption were obtained by in-situ polymerization of pyrrole monomer.The influence of the molar ratio of pyrrole monomer to oxidant and the mass fraction of paraffin wax on the structure morphology and performance of the final CNF/Fe₃O₄/PW/polypyrrole(PPy)foam was studied.The results showed that due to the high phase change enthalpy of PW as well as the synergistic effect of conductivity and magnetic properties between PPy and Fe₃O₄ nanoparticles,the composite foams exhibited multifunctional characteristics.The best reflection loss value(–55.60 d B)of the CNF/Fe₃O₄/PW/PPy foam was obtained at a thickness of 2.5 mm,and the effective bandwidth was as high as 10.0 GHz.In addition,the foams also exhibited good energy storage capacity and hydrophobicity.(3)The CNF/GO/PW/Fe₃O₄ composite foams were fabricated by freeze-drying the Pickering emulsion gels,which were obtained through emulsifying the water phase of CNF and graphene oxide(GO)aqueous dispersion and the oil phase of1,2-dichloroethane dispersion of PW and Fe₃O₄ nanoparticles.Then,C-r GO/Fe₃O₄carbon foams were obtained via high temperature annealing process.The effects of water-oil volume ratio,paraffin wax mass fraction and Fe₃O₄ concentration on the morphology and particle size of Pickering emulsion droplets,the structure morphology and performance of C-r GO/Fe₃O₄ carbon foam were studied.The results showed that the obtained carbon foam was ultralight in weight with a density of only4.6 mg/cm³ and had excellent compression resilience and fatigue resistance.The electromagnetic wave absorbing performance of carbon foams can be flexibly adjusted by adjusting the concentration of Fe₃O₄ and compressive strain.In addition,C-r GO/Fe₃O₄ carbon foam with the highly current responsiveness can be used in sensing equipment to detect human motion signals.