Research On Infrared And Microwave Compatible Materials: Preparation And Radiation Properties

Camouflage and stealth technology is one of the research hotspots of modern high-tech military.In recent years,with the rapid development of radar,infrared and other modern photoelectric detection technology,the traditional single-function stealth materials have been difficult to meet the needs of modern information warfare.Explore the multi-band compatible stealth materials has become the trend in the field of national defense science.Among them,infrared and microwave compatible stealth materials have attracted great attention due to their wide use.From the stealth mechanism of infrared and microwave,it can be concluded that a single material system is difficult to achieve an excellent infrared and microwave compatible stealth performance.Therefore,focusing on single performance and taking into account the other performance,two kinds of materials were synthesized respectively in this paper through the selection of raw materials and the structural design,one of which was an organic material with excellent low infrared emission performance and the other was an inorganic material with low-frequency microwave absorption characteristics.The compatibility performance of the two materials was studied respectively.And the infrared and microwave compatibility mechanism was further explored.The main research contents are as follows.1.Preparation,characterization and radiation properties of helical polyacetyleneA series of optically active substituted helical polyacetylenes were synthesized from L-serine-grafted propargylamine(LSA)and propargylamine(PA)through polymerization by rhodium catalyst.A snail-shaped helical polyacetylene(SHPA)was obtained when the molar ratio of LSA monomer to PA monomer was 1:1.The monomer(LSA)and copolymers poly(LSA_m-co-PA_n)were characterized by ¹H nuclear magnetic resonance,Fourier transform infrared spectroscopy,ultraviolet visible spectroscopy,circular dichroism and transmission electron microscopy.Among them,the infrared emissivity of SHPA investigated at 8-14?m was 0.541,which was much lower than that of other copolymers.The minimum reflection loss of poly(LSA₅₀-co-PA₅₀)at the frequency of 14.9 GHz was-13.3 d B at the thickness of5 mm.This was because the poly(LSA₅₀-co-PA₅₀)could form the obvious intramolecular interaction and self-assembled to a snail-shell shape by intermolecular hydrogen bonding in Me OH solution.Meanwhile,the conjugation performance of the main chain was enhanced.Consequently,the abundant hydrogen bonds formed through N-H bonding and the strong conjugate properties both could decrease the unsaturation degree,as well as change the heat conduction mode in the molecules,thereby reducing the infrared emissivity.In addition,the spiral polyacetylene material was polarized repeatedly under the action of radar wave,resulting in polarization loss.The induction current was formed in the material and produced Joule heat,which resulting in the electromagnetic wave energy dissipation.2.Preparation,characterization and radiation properties of graphene oxide TiO₂framework inlaid with TiO₂-C.Foamed TiO₂-C was prepared by heat treatment using MIL-125(Ti)as precursor.And a series of composite materials were prepared by one-step hydrothermal method and freeze drying method with different proportions of graphene oxide(GO)and foamed TiO₂-C.Among them,when the mass ratio of graphene oxide(GO)and foamed TiO₂-C reached 1:15,the self-assembled 3D coral reef-like graphene TiO₂framework inlaid with TiO₂-C was prepared.The formation of this structure was due to the fact that part of TiO₂was grown uniformly agian on the surface of graphene oxide with nucleation point,and the?-?lamination of flexible graphene sheets was formed strong network crosslinking during hydrothermal reduction.Specifically,for the 3D coral reef-like GO TiO₂framework inlaid with TiO₂-C composite in thickness of 5.0 mm,the optimal reflection loss(RL_min)was-64.4 d B in the low frequency band of 7.4 GHz,and the effective bandwidth was 3.9 GHz.The average infrared emissivity of this material was as low as 0.613,showing good low infrared radiation performance.The mechanism of infrared microwave compatible stealth performance was explored:3D coral reef-like GO TiO₂framework inlaid with TiO₂-C had high porosity,which was conducive to multiple reflection of the electromagnetic wave.In addition,the electromagnetic absorption ability of GO TiO₂multilayer and TiO₂-C was improved by multiple reflections between multilayered microstructures and the improved polarization loss(interfaces polarization and dipole polarization),as well as the enhancement of conductivity loss caused by the network cross-linked carbon layers.The lattice of nano-TiO₂in the material was small and compact,and TiO₂exhibit strong reflectivity in the near-infrared band.In addition,rutile content of TiO₂was more conducive to the enhancement of near-infrared reflectance.3.Preparation,characterization and radiation properties of organic-inorganic composites.The organic-inorganic composite PA GTTC-15 was prepared by the method of solution blending,with the helix polyacetylene and coral reef-like graphene TiO₂framework inlaid with TiO₂-C 3D material.The infrared emissivity and microwave absorption properties of the organic-inorganic composite PA GTTC-15 were studied.The infrared emissivity of PA GTTC-15 is 0.576 at 8-14?m.when the coating thickness is 3.0 mm,the reflection loss(RL)of PA GTTC-15 is-14.1 d B,and the effective bandwidth reaches to the widest frequency of 4.5 GHz.The mechanism of infrared and microwave compatibility of organic-inorganic composite materials was PA GTTC-15 explored.The decrease of infrared emissivity was mainly due to the improvement of strong conjugation,optical rotation and molecular stability of helical polyacetylene.The good conductivity of the material,as well as the strong conductivity loss and polarization loss are helpful to enhance the electromagnetic wave attenuation and achieve the broadband microwave absorption performance.