Large‐Scale, Mechanically Robust, Solvent‐Resistant, and Antioxidant MXene‐Based Composites for Reliable Long‐Term Infrared Stealth

Abstract MXene‐based thermal camouflage materials have gained increasing attention due to their low emissivity, however, the poor anti‐oxidation restricts their potential applications under complex environments. Various modification methods and strategies, e.g., the addition of antioxidant molecules and fillers have been developed to overcome this, but the realization of long‐term, reliable thermal camouflage using MXene network (coating) with excellent comprehensive performance remains a great challenge. Here, a MXene‐based hybrid network comodified with hyaluronic acid (HA) and hyperbranched polysiloxane (HSi) molecules is designed and fabricated. Notably, the presence of appreciated HA molecules restricts the oxidation of MXene sheets without altering infrared stealth performance, superior to other water‐soluble polymers; while the HSi molecules can act as efficient cross‐linking agents to generate strong interactions between MXene sheets and HA molecules. The optimized MXene/HA/HSi composites exhibit excellent mechanical flexibility (folded into crane structure), good water/solvent resistance, and long‐term stable thermal camouflage capability (with low infrared emissivity of ≈0.29). The long‐term thermal camouflage reliability (≈8 months) under various outdoor weathers and the scalable coating capability of the MXene‐coated textile enable them to disguise the IR signal of various targets in complex environments, indicating the great promise of achieved material for thermal camouflage, IR stealth, and counter surveillance.


Characterizations
The morphology and microstructure of MXene and various samples were analyzed using scanning electron microscopy (SEM) with an energy-dispersive spectrometer (EDS) on a Sigma-500, ZEISS instrument.Transmission electron microscopy (TEM) images were obtained using a Talos F200X G2 instrument with an accelerating voltage of 200 kV.The chemical compositions and structure of the materials were analyzed using a Nicolet 7000 Fourier-transform infrared (FT-IR) spectrometer and a VG Scientific ESCALab 220I-XL X-ray photoelectron spectrometer (XPS), respectively.The water contact angle of the samples was measured at room temperature using a DSA30 CA analyzer from Kruss, Germany.X-ray diffraction (XRD) analysis was performed using a Rigaku D/Max 2550 V Xray diffractor with a 2θ range of 5° to 80°.The oxidation behavior of MXene and MXene composites was analyzed via Raman spectroscopy using a spectrometer from Bruker Instruments, Germany, and a universal electricity meter.The electrical conductivity of the samples was measured using a standard four-probe tester (ST2722-SD).The infrared (IR) reflectivity (r) and transmittance (t) were measured using an FTIR spectrometer (Nicolet iS50) equipped with an infrared integrating sphere, while the IR emissivity (e) was calculated using the equation e=1-r-t.The electrical conductivity and electromagnetic interference (EMI) shielding performance were measured in the frequency range of 8.2~12.4GHz using an Agilent vector network analyzer (PNA-N5244A).The 1H cross-polarization magic angle spinning (CP/MAS) nuclear magnetic resonance (NMR) measurements were conducted on a 400 MHz NMR spectrometer from Bruker Corp., Germany.The uniaxial stress-strain tests were performed using a dynamic mechanical thermal analyzer (DMA-Q800) from TA Instruments, America.
The thermal camouflage property of MXene-based papers was evaluated using infrared thermal imagers (FLIR E60 and FOTRIC 320Pro, America).The thermal performance of the samples was characterized using thermogravimetric analysis (TA Instruments Q500, America) under an air atmosphere with a heating rate of 10 °C/min from room temperature to 750 °C.

Figure S1 .
Figure S1.(a) Photographs showing the fabrication process of MXene via the etching and

Figure S5 .
Figure S5.(a) Mapping test of a MXene/HA mixture dispersed on a silicon wafer and (b) the

Figure S6 .
Figure S6.EDS results of MXene and MXene/HA mixture dispersed on silicon wafer before and after

Figure S10 .
Figure S10.Chemical reaction between HA and HSi.

Figure S13 .
Figure S13.(a, b) SEM images of crossing-section of MXene paper with different magnifications.

Figure S15 .
Figure S15.(a) Water contact angle for HM and HMSi nanocomposite papers.(b) Structure stability

Figure S18 .
Figure S18.(a, b) SEM images of surface and crossing-section of MXene paper with different

Figure S19 .
Figure S19.(a) IR thermal images and (b) temperature curves of MXene, HM and HMSi film cover

Figure S21 .
Figure S21.(a-b) Thermal camouflage behavior of H3M3Si2 papers under various temperatures and

Figure S22 .
Figure S22.Digital and IR thermal images of "HZNU" letters cut from H3M3Si2 film directly.

Figure S23 .
Figure S23.Digital and IR thermal images of palm covered by H3M3Si2 film.

Figure S24 .
Figure S24.(a) Surface electrical resistance and EMI SE of MXene and (b) various MXene

Figure S25 .
Figure S25.Schematic illustration for thermal camouflage test of H3M3Si2 paper in the piratical

Figure S26 .
Figure S26.Evaluating thermal camouflage performance of H3M3Si2 paper in the sun environment (summer).

Figure S29 .
Figure S29.IR thermal images and SEM images of MXene-based papers before long-term oxidation measure.

Figure S30 .
Figure S30.SEM image of the MXene paper surface after 4 months at room-temperature storage.

Figure S31 .
Figure S31.The element ratio of MXene paper surface and H3M3Si2 paper surface before and after 4 months at room-temperature storage.

Figure S32 .
Figure S32.SEM images and Mapping tests of H3M3Si2 paper (a) before and (b) after immersed in seawater for 50 days.

Figure S33 .
Figure S33.XRD patterns of H3M3Si2 paper (a) before and (b) after immersed in seawater for 50 days.

Figure S36 .
Figure S36.Combining low emissive material with thermal insulation aerogel.(a) The preparation of H3M3Si2/Glass fiber@silicone aerogel.(b) Comparison of thermal camouflage property of various samples on the 450 °C hot stage， and (c) corresponding to radiation temperature-time curves.

Table S1 .
A comparison of comprehensive properties with different MXene-based materials.