Functionally graded materials (FGMs) and functionally graded structures (FGSs) are special types of advanced composites with peculiar features and advantages. This article reviews the design criteria of functionally graded additive manufacturing (FGAM), which is capable of fabricating gradient components with versatile functional properties. Conventional geometrical‐based design concepts have limited potential for FGAM and multi‐scale design concepts (from geometrical patterning to microstructural design) are needed to develop gradient components with specific graded properties at different locations. FGMs and FGSs are of great interest to a larger range of industrial sectors and applications including aerospace, automotive, biomedical implants, optoelectronic devices, energy absorbing structures, geological models, and heat exchangers. This review presents an overview of various fabrication ideas and suggestions for future research in terms of design and creation of FGMs and FGSs, benefiting a wide variety of scientific fields.
Most previous fiber-shaped solar cells were based on photoelectrochemical systems involving liquid electrolytes, which had issues such as device encapsulation and stability. Here, we deposited classical semiconducting polymer-based bulk heterojunction layers onto stainless steel wires to form primary electrodes and adopted carbon nanotube thin films or densified yarns to replace conventional metal counter electrodes. The polymer-based fiber cells with nanotube film or yarn electrodes showed power conversion efficiencies in the range 1.4% to 2.3%, with stable performance upon rotation and large-angle bending and during long-time storage without further encapsulation. Our fiber solar cells consisting of a polymeric active layer sandwiched between steel and carbon electrodes have potential in the manufacturing of low-cost, liquid-free, and flexible fiber-based photovoltaics.
The development of stimuli-responsive materials with the ability of controllable oil/water separation is crucial for practical applications. Here, a novel pH responsive nonfluorine-containing copolymer was designed. The copolymer together with silica can be dip-coated on different materials including cotton fabric, filter paper, and polyurethane foam. The coated materials exhibit switchable superhydrophilicity and superhydrophobicity and can be applied in continuous separation of oil/water/oil three phase mixtures, different surfactant stabilized emulsion (oil-in-water, water-in-oil, and oil-in-acidic water) as well as oil uptake and release via in situ and ex situ pH change. We expect that the coatings highlight the practical applications because of the cost-effective preparation process and fluorine-free strategy.
The
ability to allow microliquid to penetrate in one direction
but block in the opposite direction plays an irreplaceable role in
intelligent liquid management. Despite much progress toward facilitating
directional transport by multilayer porous membranes with opposite
wettability, it remains difficult to achieve a highly multifunctional
flexible membrane for highly efficient unidirectional liquid transport
in different situations. Herein, a superhydrophilic–hydrophilic
self-supported monolayered porous poly(ether sulfone) (PES) membrane
with special nano- and micropores at opposite surfaces is demonstrated,
which can be used for unidirectional liquid transport. The results
reveal that the competition of liquid spreading and permeation is
critical to achieve directional liquid transport. The porous PES membrane,
transformed with 70 vol % of ethanol in water (E/W-PES-70%), exhibits
continuous unidirectional liquid penetration and antigravity unidirectional
ascendant in a large range of pH values and can be used as “liquid
diode” for moisture wicking. Moreover, the PES membrane can
be prepared in a large area with excellent flexibility at room and
liquid nitrogen temperature, indicating great promise in harsh environments.
This work will provide an avenue for designing porous materials and
smart dehumidification materials, which have promising applications
in biomedical materials, advanced functional textiles, engineered
desiccant materials, etc.
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