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Polymers often have thermal conductivities that are too low to be used directly in thermal management applications. In this study, a poly(p‐phenylene‐2,6‐benzobisoxazole) (PBO) film is prepared through a sol–gel‐film conversion and annealing method that utilizes PBO nanofibers as building blocks. The polymer film shows an in‐plane thermal conductivity of 36.7 W mK−1, which is two orders of magnitude higher than those of most polymers (<0.5 W mK−1) and 2.4 times that of 304‐stainless steel. The high thermal conductivity is attributed to the highly oriented 3D interconnected nanofiber network resulting from the fine‐tuning sol‐gel‐film conversion, and the annealing that further enhances the ordering of the PBO chains and the interactions between the nanofibers. Moreover, the PBO films exhibit excellent mechanical strength, thermal/chemical stability, electrical insulation, flame retardance, and improved UV resistance. The lightweight, robust, and easily processed PBO film with a metal‐like thermal conductivity has promising potential thermal management applications. [ABSTRACT FROM AUTHOR]

Passive daytime radiation cooling (PDRC) has gained considerable attention as an emerging and promising cooling technology. Polymer‐based porous materials are one of the important candidates for PDRC application due to their easy processing, free of inorganic particle doping, and multifunctionality. However, the mechanical properties of these porous materials, which are critical in outdoor services, have been overlooked in previous studies. Herein, a nonsolvent‐induced phase separation (NIPS) method combined with ambient pressure drying to prepare polyethylene‐polysilicate all‐polymer porous coatings is developed. The coatings possess a Cyphochilus beetle‐like skeleton structure with optimal skeleton size, laminated anisotropy, and high volume fraction (64 ± 1%). These structure features ensure a maximum skeleton density without optical crowding, thus enhancing light scattering and stress dispersion, and balancing optical and mechanical properties. The coatings exhibit significant mechanical robustness (only ≈70 µm thickness reduction after 1000 Taber abrasion cycles at a 750 g load without influencing optical performance), durability, optical properties (a solar reflectance of ≈95% and an average near‐normal thermal emittance of ≈96%), and PDRC performance (realizing sub‐ambient cooling of ≈3–6 °C at midday with different weather conditions). The work provides a new solution to improve the practicability of polymer‐based porous coatings in PDRC outdoor services and other fields. [ABSTRACT FROM AUTHOR]

Vat‐photopolymerization‐based 3D printing enables on‐demand construction of customized objects with scalable production capacity and high precision. Herein, the sol‐gel process for aerogels with digital light processing 3D printing to produce advanced functional materials possessing hierarchical pore structures and complex shapes is combined. It has revealed the temporal evolution of the photorheological behavior of acrylate‐modified silica sols in an acid‐base catalytic procedure, and confirmed that silica aerogels can be fabricated with very low acrylate content. The resulting aerogels are thermostable with intrinsic silica contents, skeletal densities, and physical characteristics similar to those of commercial silica aerogels yet distinct mechanical behaviors. More importantly, the printed silica aerogels can be used as a versatile nanoengineering platform to produce high‐performance and multifunctional interpenetrating phase nanocomposites with complex shapes through programmable post‐printing processes. Epoxy‐based nanocomposites possessing excellent mechanical performance, ionogel‐based conductive nanocomposites with decoupled electrical and mechanical properties, and anti‐swelling hydrogel‐based nanocomposites are demonstrated. The results of this study offer new guidelines for the design and fabrication of novel materials by additive manufacturing. [ABSTRACT FROM AUTHOR]

Herein, dual‐tunable structural colors generated from liquid‐infused, robust silsesquioxane aerogels due to the specific light scattering by the aerogel skeleton in liquids with matching refractive indices, are reported. The colors are tunable by changing the temperature and the composition of the liquid that roots from the coherence between the colors and the refractive index of the infused liquid. The finding provides new insights and tools for constructing structural colors and light management. It also opens applications of stimuli‐responsive smart windows, displays, and sensors. Taking advantage of the penetrable light of selected wavelength, the 3D structures of aerogel skeletons are reconstructed by an optical method, which provides a facile alternative approach to characterizing aerogel structure and will be instrumental to the understanding of the relationship between skeleton structure and mechanical property of porous 3D structures. [ABSTRACT FROM AUTHOR]

Smart fluids with tunable rheological properties show a wide range of applications in various areas, so they have attracted intense interest. Recently, the viscoelastic fluids with tunable rheological properties, particularly the CO 2 -triggered smart fluids, have become a popular topic because such reversible change in viscoelasticity conferring them new functions and expanding their applications. Additionally, anioinc polymers can be crosslinked to impart fluids significantly improved rheological properties. Herein, Sodium polyacrylate (NaPAA) and 2,4,6-tris(dimethylaminomethyl)phenol (TAP) are employed to prepare aqueous fluid. The solution properties of the fluid with and without CO 2 are examined by steady and dynamical rheology. The effects of NaCl concentration and the ratio of NaPAA/TAP on the rheologies are studied and the interactions between TAP and NaPAA in the absence and presence of CO 2 are investigated using pH titration, 1H NMR and cryo-TEM technology. CO 2 is able to reversibly change the rheological properties of the fluid via protonating and deprotonating TAP, imparting it smart response. In the absence of NaCl, the introduction of the CO 2 reduces the viscosity and elasticity of the fluid as the produced quaternary ammonium salts largely screen the electrostatic repulsions of NaPAA chains. However, in the presence of NaCl, the addition of CO 2 greatly enhances the viscoelasticity of the fluid because the protonated TAP strongly interacts with NaPAA forming three-dimensional networks. Unlabelled Image • CO 2 gas can reversibly change rheological properties of NaPAA-TAP complexed fluid. • CO 2 -responsiveness on rheological properties can be regulated. • CO 2 protonated TAP plays the role of "crosslinker" for NaPAA. [ABSTRACT FROM AUTHOR]

The scales of the white Cyphochilus beetles are endowed with unusual whiteness arising from the exceptional scattering efficiency of their disordered ultrastructure optimized through millions of years of evolution. Here, a simple, one‐step method based on water vapor–induced phase separation is developed to prepare thin polystyrene films with similar microstructure and comparable optical performance. A typical biomimetic 3.5 µm PS film exhibits a diffuse reflectance of 61% at 500 nm wavelength, which translates into a transport mean free path below 1 µm. A complete optical characterization through Monte Carlo simulations reveals how such a scattering performance arises from the scattering coefficient and scattering anisotropy, whose interplay provides insight into the morphological properties of the material. The potential of bright‐white coatings as smart sensors or wearable devices is highlighted using a treated 3.5 µm film as a real‐time sensor for human exhalation. [ABSTRACT FROM AUTHOR]