Efficient Electromagnetic Wave Absorption and Thermal Infrared Stealth in PVTMS@MWCNT Nano‑Aerogel via Abundant Nano‑Sized Cavities and Attenuation Interfaces

Pre-polymerized vinyl trimethoxy silane(PVTMS)@MWCNT nano-aerogel system was constructed via radical polymerization,sol-gel transition and supercritical CO_(2)drying.The fabricated organic-inorganic hybrid PVTMS@MWCNT aerogel structure shows nano-pore size(30-40 nm),high specific surface area(559 m^(2)g^(−1)),high void fraction(91.7%)and enhanced mechanical property:(1)the nano-pore size is beneficial for efficiently blocking thermal conduction and thermal convection via Knudsen effect(beneficial for infrared(IR)stealth);(2)the heterogeneous interface was beneficial for IR reflection(beneficial for IR stealth)and MWCNT polarization loss(beneficial for electromagnetic wave(EMW)attenuation);(3)the high void fraction was beneficial for enhancing thermal insulation(beneficial for IR stealth)and EMW impedance match(beneficial for EMW attenuation).Guided by the above theoretical design strategy,PVTMS@MWCNT nano-aerogel shows superior EMW absorption property(cover all Ku-band)and thermal IR stealth property(ΔT reached 60.7℃).Followed by a facial combination of the above nano-aerogel with graphene film of high electrical conductivity,an extremely high electromagnetic interference shielding material(66.5 dB,2.06 mm thickness)with superior absorption performance of an average absorption-to-reflection(A/R)coefficient ratio of 25.4 and a low reflection bandwidth of 4.1 GHz(A/R ratio more than 10)was experimentally obtained in this work.

Ni Flower/MXene-Melamine Foam Derived 3D Magnetic/Conductive Networks for Ultra-Efficient Microwave Absorption and Infrared Stealth

The development of multifunctional and efficient electromagnetic wave absorbing materials is a challenging research hotspot.Here,the magnetized Ni flower/MXene hybrids are successfully assembled on the surface of melamine foam(MF)through electrostatic self-assembly and dip-coating adsorption process,realizing the integration of microwave absorption,infrared stealth,and flame retardant.Remarkably,the Ni/MXene-MF achieves a minimum reflection loss(RLmin)of−62.7 dB with a corresponding effective absorption bandwidth(EAB)of 6.24 GHz at 2 mm and an EAB of 6.88 GHz at 1.8 mm.Strong electromagnetic wave absorption is attributed to the three-dimensional magnetic/conductive networks,which provided excellent impedance matching,dielectric loss,magnetic loss,interface polarization,and multiple attenuations.In addition,the Ni/MXene-MF endows low density,excellent heat insulation,infrared stealth,and flame-retardant functions.This work provided a new development strategy for the design of multifunctional and efficient electromagnetic wave absorbing materials.

Highly oriented MXene/polyvinyl alcohol films prepared by scalable layer-by-layer blade coating for efficient electromagnetic interference shielding and infrared stealth

Controlling the orientation of two-dimensional MXene within layered films is essential to optimize or tune their mechanical properties and electromagnetic interference shielding(EMI)performance,but achieving the high orientation MXene layers on an industrial scale remains a challenging goal.In this paper,a scalable layer-by-layer blade coating(LbLBC)method was employed to fabricate highly oriented MXene/polyvinyl alcohol(PVA)films.During the LbLBC process,MXene/PVA colloid suffered a strong shearing effect,which induced the ordered alignment of MXene nanosheets along the direction of the blade movement.The orientation of MXene can be effectively adjusted by changing the scraping gap of LbLBC,achieving a maximum Herman orientation factor f of 0.81.As a result,the mechanical properties and EMI performance of the as-prepared MXene/PVA films are in direct proportion to their orientation,with the optimal values of tensile strength of 145.5 MPa,fracture strain of 19.6%,toughness of 17.7 MJ·m^(−3),and EMI shielding effectiveness of 36.7 dB.Furthermore,the inherently low mid-infrared(mid-IR)emissivity of MXene,combined with the densely oriented structure affords the composite films with IR stealth,resulting in a substantial decrease from 150 to 66.1℃in the radiative temperature of a surface.Conclusively,these scalable MXene/PVA films exhibit remarkable potential for integration into the next generation of multifunctional protective camouflage materials.

Research on Infrared Emissivity and Laser Reflectivity of Sn_(1−x)Er_(x)O_(2)Micro/Nanofibers Based on First-Principles

Sn_(1−x)Er_(x)O_(2)(x=0%,8%,16%,24%)micro/nanofibers were prepared by electrospinning combined with heat treatment using erbium nitrate,stannous chloride and polyvinylpyrrolidone(PVP)as raw materials.The target products were characterized by thermogravimetric analyzer,X-ray diffrotometer,fourier transform infrared spectrometer,scanning electron microscope,spectrophotometer and infrared emissivity tester,and the effects of Er^(3+)doping on its infrared and laser emissivity were studied.At the same time,the Sn_(1−x)Er_(x)O_(2)(x=0%,16%)doping models were constructed based on the first principles of density functional theory,and the related optoelectronic properties such as their energy band structure,density of states,reflectivity and dielectric constant were analyzed,and further explained the mechanism of Er^(3+)doping on SnO_(2)infrared emissivity and laser absorption from the point of electronic structure.The results showed that after calcination at 600℃,single rutile type SnO_(2)was formed,and the crystal structure was not changed by doping Er^(3+).The calcined products showed good fiber morphology,and the average fiber diameter was 402 nm.The infrared emissivity and resistivity of the samples both decreased first and then increased with the increase of Er^(3+)doping amount.When x=16%,the infrared emis-sivity of the sample was at least 0.71;and Er^(3+)doping can effectively reduce the reflectivity of SnO_(2)at 1.06μm and 1.55μm,when x=16%,its reflectivity at 1.06μm and 1.55μm are 50.5%and 40%,respectively,when x=24%,the reflectivity at 1.06μm and 1.55μm wavelengths are 47.3%and 42.1%,respectively.At the same time,the change of carrier concentration and electron transition before and after Er^(3+)doping were described by first-principle calculation,and the regulation mechanism of infrared emissivity and laser reflectivity was explained.This study provides a certain experimental and theoretical basis for the development of a single-type,light-weight and easily prepared infrared and laser compatible-stealth material.

Preparation of ZAO powder and investigation on its infrared emissivity

According to the basic infrared stealth mechanism of low infrared emissivity powders,the ZAO powder materials were prepared by liquid coprecipitation method,and the starting materials were Zn( NO3) 6H2O and Al( NO3) 39H2O. The process parameters were obtained,and the relationship between technology parameters and infrared emissivity was investigated. The temperature of thermal treatment,crystal structure and surface micrograph of ZAO powder was analyzed by the help of TG-DTA,XRD and SEM. The infrared stealth performance of ZAO powder was studied by IR-2 emissivity spectroscopy. Results showed that the infrared emissivity was the lowest when pH was 8. 0,calcination temperature was 1100 ℃,calcination time was 2 h,and the Al2O3doping content was 3% ( mass percentage) . The crystal structure of doped ZAO powder was lead-zinc, and there exists distortion of crystal lattice in nanocrystalline ZnO. The average particle size was 10 μm. The lowest infrared emissivity reached to 0. 61 at between 8 μm and 14 μm. It means that the ZAO powders will be excellent infrared stealthy materials.

Coupling of Epsilon-Near-Zero Mode to Mushroom-Type Metamaterial for Optimizing Infrared Suppression and Radiative Cooling

We report a complementary metal oxide semiconductor(CMOS)compatible metamaterial-based spectrally selective absorber/emitter(MBSSAE)for infrared(IR)stealth,which has the low absorption/emissivity in the IR atmospheric transmission window(3μm-5μm,8μm-14μm)and ultra-high and broadband absorption/emissivity in the IR non-atmospheric window(5μm-8μm).We propose a novel method for the broadband absorption/emissivity in 5μm-8μm with incorporation of an epsilon-near-zero(ENZ)material between the top patterned aluminum(Al)disks layer and the silicon oxide(SiO_(2))spacer layer.With an appropriate design,the peaks in the IR atmospheric transmission window can be suppressed while the peak intensity in the non-atmospheric window remains high.The optimized MBSSAE has an average absorption/emissivity less than 10%in 8μm-14μm and less than 6%in 3μm-5μm.And the average absorption/emissivity in 5μm-8μm is approximately over 64%.This proposed scheme may introduce the opportunities for the large-area and low-cost infrared stealth coating,as well as for the radiative cooling,spectral selective thermal detector,optical sensor,and thermophotovoltaic applications.

Multi-functional and multi-scenario applications for MXene aerogels with synergistically enhanced asymmetric modules

The development of multifunctional materials and synergistic applications of various functions are important conditions for integrated and miniaturized equipment.Here,we developed asymmetric MXene/aramid nanofibers/polyimides(AMAP)aerogels with different modules using an integrated molding process.Cleverly asymmetric modules(layered MXene/aramid nanofibers section and porous MXene/aramid nanofibers/polyimides section)interactions are beneficial for enhanced performances,resulting in low reflection electromagnetic interference(EMI)shielding(specific shielding effectiveness of 2483(dB·cm^(3))/g and a low R-value of 0.0138),high-efficiency infrared radiation(IR)stealth(ultra-low thermal conductivity of 0.045 W/(m·K)and IR emissivity of 0.32 at 3–5μm and 0.28 at 8–14μm),and excellent thermal management performances of insulated Joule heating.Furthermore,these multifunctional AMAP aerogels are suitable for various application scenarios such as personal and building protection against electromagnetic pollution and cold,as well as military equipment protection against infrared detection and EMI.

Numerical study of a trapezoidal bypass dual throat nozzle

Bypass Dual Throat Nozzle(BDTN)is a novel type of fluidic thrust vectoring nozzle.To improve the infrared stealth performance of BDTN,a nozzle based on BDTN is proposed and numerically simulated.Each cross-section along the x-axis of the novel nozzle becomes a trapezoid,which is named“BDTN-TRA.”The main numerical simulation results show that BDTN-TRA can produce a thrust vectoring angle when the upper or lower bypass valve is open.The angle difference between the two conditions mentioned above is usually approximately 1°-2°.Even if the two bypasses are closed,BDTN-TRA can produce a small thrust vectoring angle at around 3°-5°.When the sidewall angle increases from 60°to 90°,the thrust coefficient and thrust vectoring angle under each work condition usually decrease.A larger aspect ratio indicates better performance.As the aspect ratio increases over 7.2,the performance of BDTN-TRA is quite close to that of BDTN with rectangular cross-sections at the same aspect ratio.These features will benefit the control and trimming for future aircraft design,especially for the flying wing layout aircraft.Last but not least,BDTN-TRA has a more extraordinary mixing performance compared with BDTN.The distributions of static temperature and axial velocity along the x-axis of BDTN-TRA with sidewall angle of 60°decrease faster than those of BDTN.When the total temperature of the inlet equals 1600 K,the static temperature difference between BDTN-TRA with sidewall angles of 60°and 90°is over 360 K at twice the length of the nozzle downstream of the nozzle exit,which is the reflection for excellent infrared stealth for the fighter.

Multifunctional protective aerogel with superelasticity over−196 to 500℃

Protective materials that possess superelasticity and multifunctionality over a broad temperature range are urgently needed in various advanced applications.However,under harsh work conditions,the performance of current materials may largely deteriorate to lose protective functionality.Herein,we report a bidirectionally oriented multi-walled carbon nanotubes(MWCNTs)-reinforced chitosan carbon aerogel(CS-MWCNT)that possesses superelasticity,high electromagnetic interference shielding,thermal insulation,and infrared stealth at both low temperatures(such as liquid nitrogen)and high temperatures(such as alcohol flames).Highly oriented lamellar arch structures combined with an MWCNTs-reinforced carbon skeleton act as elastic segments to disperse the stress during compression and endow CS-MWCNT with the ability to recover to almost the original size after being compressed at−196-500℃.The lamellar structures make CS-MWCNT thermally insulating and infrared stealth with a low thermal conductivity of~0.03 W/(m·K).Furthermore,a high electromagnetic interference(EMI)shielding effect of 64 dB is realized via an absorption-dominant EMI shielding mechanism derived from the successive inherently conductive carbon lamella,and the EMI shielding performance is largely maintained after treatment under extreme conditions like low temperature,high temperature,as well as cyclic compression.This work provides a new strategy for the development of temperature-invariant multifunctional aerogels for harsh environment applications.