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

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.

Thermal Stability and Weather Resistance of a Bionic Lotus Multiscale Micro-Nanostructure TiC/TiN-Ni/Mo Spectral Selective Absorber Based on Laser Cladding-Induced Melt Foaming.

As the core of a solar collector, a solar selective absorbing coating has become the key material for efficient utilization and development of solar energy. In order to overcome the core scientific problem of poor high-temperature stability of optical properties caused by atomic diffusion between layers in the high-temperature environment of traditional multilayer solar absorption coatings, the multiscale lotus bionic porous structure was constructed by using a TiC/TiN-Ni/Mo material system with excellent intrinsic absorption performance. The melt foam method and laser cladding technology were combined to deposit the multiscale bionic porous structure solar selective absorption coating in situ by a laser-induced melt foaming strategy. It was found that the bubbles in the molten pool were affected by Marangoni force, gravity, buoyancy, and surface tension. The unescaped bubbles formed pores near the surface of the coating and showed a bimodal distribution. For the multiscale addition of 1.8 and 0.4 µm pore-forming agents with a mass fraction of 15 wt %, the multiscale pores enhance the scattering and secondary absorption of light and reduce the amplitude of electromagnetic wave to electron vibration; at the same time, the small-size conductor effect formed by the hole increases the surface electron concentration, strengthens the absorption of light, and enhances the magnetic field strength at the hole, and the structural absorbing effect is significant. The coating absorptivity α reaches 85%, and the temperature stability is excellent. Compared with the substrate, the coating has a smaller corrosion current density, larger polarization resistance, and strong corrosion resistance. The research shows that the laser-induced multiscale bionic porous structure coating obtains the intrinsic absorption-structural absorption composite absorption mechanism and realizes the integration of flexible design and efficient manufacturing of high-temperature solar absorption coatings.

Structural Porous Ceramic for Efficient Daytime Subambient Radiative Cooling.

Radiative cooling enables the passive cooling of buildings without energy input. Structural radiative cooling materials, such as cellulose-based composites, have recently received extensive attention due to their exceptional mechanical properties and spectral selectivity. However, the cellulose-based materials face challenges in durability and flame resistance, which limits their practical application. Herein, a structural porous Si3N4-BN ceramic with a high solar reflectivity of ∼0.95 and an atmospheric window emissivity of ∼0.95 was prepared by one-step combustion synthesis. The porous ceramic achieves a subambient radiative cooling performance of 5.14 °C under direct sunlight and theoretically yields a cooling power of 78.55 W m-2. The network structure of Si3N4 crystals leads to a flexural strength of 31.07 MPa and a compressive strength of 65.36 MPa. The porous Si3N4-BN ceramics with excellent radiative cooling performance, mechanical properties, and thermal insulation exhibit wide application prospects in building cooling, especially in the harsh environment of tropical desert and island regions.

Improvement of the Weather Resistance of a Selective Laser-Sintered Copolyester-Limestone Composite Using UV-326 and UV-328.

A copolyester-limestone composite fabricated with selective laser sintering technology is a potential material for the repair of ancient brick structures damaged by the sun and rain, however the weather resistance of this material must be improved. Herein, UV-236 and UV-328 were employed as UV stabilizers and added into the composite. The results show that the addition of UV-326 and UV-328 effectively inhibited the degradation of CH and ester groups and the formation of hydroxyl, carbonyl, and carboxyl groups. Thus, the stabilizers significantly reduced the color change and decline in mechanical properties of the composite under sun and rain conditions. The proposed strategy can be used for the repair of damaged precious brick buildings.