Biosustainable Multiscale Transparent Nanocomposite Films for Sensitive Pressure and Humidity Sensors.

Light weight, thinness, transparency, flexibility, and insulation are the key indicators for flexible electronic device substrates. The common flexible substrates are usually polymer materials, but their recycling is an overwhelming challenge. Meanwhile, paper substrates are limited in practical applications because of their poor mechanical and thermal stability. However, natural biomaterials have excellent mechanical properties and versatility thanks to their organic-inorganic multiscale structures, which inspired us to design an organic-inorganic nanocomposite film. For this purpose, a bio-inspired multiscale film was developed using cellulose nanofibers with abundant hydrophilic functional groups to assist in dispersing hydroxyapatite nanowires. The thickness of the biosustainable film is only 40 µm, and it incorporates distinctive mechanical properties (strength: 52.8 MPa; toughness: 0.88 MJ m-3) and excellent optical properties (transmittance: 80.0%; haze: 71.2%). Consequently, this film is optimal as a substrate employed for flexible sensors, which can transmit capacitance and resistance signals through wireless Bluetooth, showing an ultrasensitive response to pressure and humidity (for example, responding to finger pressing with 5000% signal change and exhaled water vapor with 4000% signal change). Therefore, the comprehensive performance of the biomimetic multiscale organic-inorganic composite film confers a prominent prospect in flexible electronics devices, food packaging, and plastic substitution.

Transpiration-induced self-growth of texture hydrogel surfaces.

Trees grow by coupling the transpiration-induced nutrient absorption from external sources and photosynthesis-based nutrient integration. Inspired by this manner, we designed a class of polyion complex (PIC) hydrogels containing isolated liquid-filled voids for growing texture surfaces. The isolated liquid-filled voids were created via irreversible matrix reconfiguration in a deswelling-swelling process. During transpiration, these voids reversibly collapse to generate negative pressures within the matrices to extract polymerizable compounds from external sources and deliver them to the surface of the samples for photopolymerization. This growth process is spatial-controllable and can be applied to fabricate complex patterns consisting of different compositions, suggesting a new strategy for making texture surfaces.

Ostwald ripening for designing time-dependent crystal hydrogels.

Ostwald ripening (OR), a classic solution theory describing molecular transfer from metastable crystal to stable one, is applied to design time-dependent crystal hydrogels that can automatically change their mechanical properties. Using a system made from crosslinked polyacrylamide (PAM) and sodium acetate (NaAc), we demonstrate that metastable fibrous crystal networks of NaAc preferably form in PAM hydrogels via a polymer-involving mismatch nucleation. These fibrous crystals would undergo OR and evolve into isolated bulk crystals, leading to a significant reduction in material rigidity (179 folds) and interfacial adhesion (20 folds). This transformation can be applied to program time-dependent self-recovery in shape and self-delamination. Since OR is a ubiquitous, robust feature of various crystals, the approach reported here represents a new direction for designing advanced transient soft materials.

Self-growing photonic composites with programmable colors and mechanical properties.

Many organisms produce stunning optical displays based on structural color instead of pigmentation. This structural or photonic color is achieved through the interaction of light with intricate micro-/nano-structures, which are "grown" from strong, sustainable biological materials such as chitin, keratin, and cellulose. In contrast, current synthetic structural colored materials are usually brittle, inert, and produced via energy-intensive processes, posing significant challenges to their practical uses. Inspired by the brilliantly colored peacock feathers which selectively grow keratin-based photonic structures with different photonic bandgaps, we develop a self-growing photonic composite system in which the photonic bandgaps and hence the coloration can be easily tuned. This is achieved via the selective growth of the polymer matrix with polymerizable compounds as feeding materials in a silica nanosphere-polymer composite system, thus effectively modulating the photonic bandgaps without compromising nanostructural order. Such strategy not only allows the material system to continuously vary its colors and patterns in an on-demand manner, but also endows it with many appealing properties, including flexibility, toughness, self-healing ability, and reshaping capability. As this innovative self-growing method is simple, inexpensive, versatile, and scalable, we foresee its significant potential in meeting many emerging requirements for various applications of structural color materials.

A self-cleaning zwitterionic nanofibrous membrane for highly efficient oil-in-water separation.

The oil and bacteria adhesion during membrane separation process brings great challenges to the operation costs and membrane service life. Meantime, the strong chemical corrosion in sewage seriously limits the durability of membrane as well. Herein, a facile strategy is developed for fabricating highly stable and efficient zwitterionic nanofibrous membrane (NFM) with self-cleaning feature via the combination of in-situ cross-linking of poly (sulfobetaine methacrylate) (PSBMA) and electrospun poly (ether sulfone) (PES) nanofibers. Owing to the introduction of zwitterionic functional groups, the PSBMA/PES NFM exhibits superior antifouling ability (over 3 cycles of crude oil fouling/self-cleaning and up to 7 days of bacteria adhesion/repelling tests). Moreover, the membrane also presents remarkable chemical stability in acidic, alkaline and salty environments; and exhibits excellent separation performance for both layered oil/water mixture and oil-in-water emulsion as well. Furthermore, the membrane is capable to remove bacteria during the continuous oil/water mixture separation. Overall, the proposed strategy provides a new perspective into developing long-term antifouling membrane materials for complicated oily wastewater remediation in various corrosive environments.