Fabrication of transparent and superhydrophobic nanopaper via coating hybrid SiO2/MWCNTs composite

Design and Synthesis of a Robust and Multifunctional Superhydrophobic Coating with a Three-Dimensional Network Structure on a Paper-Based Material

A fundamental challenge in artificial superhydrophobic papers is their poor resistance to mechanical abrasion, which limits their practical application in different fields. Herein, a robust and multifunctional superhydrophobic paper is successfully fabricated via a facile spraying method by combining silver nanowires and fluorinated titania nanoparticles through a common paper sizing agent (alkyl ketene dimer) onto paper. It is shown that the surface of the paper-based material presents a three-dimensional network structure due to the cross-linking of silver nanowires with a high aspect ratio. Further hydrophilic and hydrophobic performance test results show that it exhibits exceptional water repellency, with a desirable static contact angle of 165° and roll-off angle of 6.2°. The superhydrophobic paper showcases excellent mechanical durability and maintains its superhydrophobicity even after enduring 130 linear sandpaper abrasion cycles or high-velocity water jetting impact benefited from interfacial van der Waals and hydrogen bonding. Simultaneously, the robust superhydrophobic surface can effectively prevent the penetration of acid or alkali solutions, as well as UV light, resulting in excellent chemical stability. Additionally, the superhydrophobic paper offers supplementary features such as self-cleaning, electrical conductivity, and antibacterial capability. Further development of this strategy paves a way toward next-generation superhydrophobic paper composed of nanostructures and characterized by multiple (or additional) functionalities.

High-Performance Flexible Ionically Conductive Superhydrophobic Papers via Deep Eutectic Polymer-Enhanced Interfacial Interactions

Endowing paper with highly flexible, conductive, and superhydrophobic properties will effectively expand its applications in fields such as green packaging, smart sensing, and paper-based electronics. Herein, a multifunctional superhydrophobic paper is reported in which a highly flexible transparent conductive substrate is prepared by introducing a hydrophobic deep eutectic polymer into the ethylcellulose network via a matrix swelling-polymerization strategy, and then the substrate is modified using fluorinated silica to impart superhydrophobicity. By introducing soft deep eutectic polymers, (1) the superhydrophobic paper can efficiently dissipate energy during deformation, (2) intrinsically ion-conducting deep eutectic polymers can endow the material with good electrical sensing properties, and (3) meanwhile, enhanced interfacial interactions can anchor inorganic particles, thereby improving the coating stability. The prepared superhydrophobic paper has an ultrahigh water contact angle (contact angle ≈ 162.2°) and exhibits a stable electrical response signal to external deformation/pressure, and the electrical properties are almost unaffected by external water molecules. In addition, the superhydrophobic paper was able to withstand 5000 bending-recovery cycles at a large angle of 150°, exhibiting stable electrical performance. The design concepts demonstrated here will provide insights into the development of superhydrophobic paper-based flexible electronic devices.

A Brief Review on Flexible Electronics for IoT: Solutions for Sustainability and New Perspectives for Designers

The Internet of Things (IoT) is gaining more and more popularity and it is establishing itself in all areas, from industry to everyday life. Given its pervasiveness and considering the problems that afflict today's world, that must be carefully monitored and addressed to guarantee a future for the new generations, the sustainability of technological solutions must be a focal point in the activities of researchers in the field. Many of these solutions are based on flexible, printed or wearable electronics. The choice of materials therefore becomes fundamental, just as it is crucial to provide the necessary power supply in a green way. In this paper we want to analyze the state of the art of flexible electronics for the IoT, paying particular attention to the issue of sustainability. Furthermore, considerations will be made on how the skills required for the designers of such flexible circuits, the features required to the new design tools and the characterization of electronic circuits are changing.

Superhydrophobic modification of cellulosic paper-based materials: Fabrication, properties, and versatile applications

Cellulose is the cheapest and mostly widespread green raw material on earth. Due to the easy and versatile developed modification of cellulose, many cellulosic paper-based sustainable materials and their multifunctional applications have attained increasing interest under the background of the implementation of the "plastic ban" policy. However, intrinsic cellulose paper is hydrophilic and non-water-proof, which highly limited its application, thus becoming a bottleneck for the development of "cellulosic paper-based plastic replacement". Unquestioningly, the superhydrophobic modification of cellulosic paper-based materials and the extension of their high value-added applications are highly desired, which is the main content of this review. More importantly, we presented the comprehensive discussion of the functionalized applications of superhydrophobic cellulosic paper-based materials ranging from conventional products to high value-added functional materials such as paper straw and paper mulch film for the first time, which have great industrialization potential and value. This review would offer the valuable guidance and insightful information for the rational construction of sustainable superhydrophobic cellulosic paper for advanced functional devices.

Cellulose nanofiber assisted dispersion of hydrophobic SiO2 nanoparticles in water and its superhydrophobic coating

It is challenging to build a superhydrophobic coating with aqueous dispersions since hydrophobic substances are usually dispersed in pure organic or water/organic mixed solvents. In this study, hydrophobic SiO₂ nanoparticles were dispersed in water assisted with cellulose nanofiber (CNF) and the superhydrophobic surface was manufactured by coating a waterborne dispersion composed of CNF, hydrophobic SiO₂ nanoparticles and methyltrimethoxysilane (MTMS). It was found that the dispersion of SiO₂ in water can be improved by CNF. Meanwhile, the coated paper surface retained its hydrophobicity after 10 abrasion cycles due to the adhesion of the coating surface promoted by MTMS. When SiO₂ content over 0.25 wt%, the coated paper surface displayed a superhydrophobic property, and the moisture absorption decreased to 31-34%. The contact angle of the coating surface was 162°, the contact angle hysteresis was 1.96° and the rolling contact angle was 1.33° when SiO₂ content was 1 wt%.

Multivalent Metal Ion Cross-Linked Lignocellulosic Nanopaper with Excellent Water Resistance and Optical Performance

Cellulose nanopaper is an attractive film material exhibiting huge potential in various fields, while its terrible water stability greatly hinders practical applications. Previous efforts on addressing this issue usually sacrifice the sustainability or material performance of film. In this study, we report a high-performing lignocellulosic nanopaper with superior water resistance and excellent optical properties. The strategy involves preparing a lignin-containing cellulose nanopaper (LCNP) first, and then infiltrating metal ions into the film to build cross-linking interactions within the fiber networks. Owing to the coordination bonds formed between metal ions and lignocellulosic components, the resulting metal ions cross-linked LCNP (M⁺-LCNP) displays outstanding water resistance, including the highest wet mechanical strength of ∼52 MPa after immersing in water for 24 h, which retains nearly 47% of the dry mechanical strength of the film. The ultralow water uptake ratio of ∼35% also confirms it possesses a superior wet dimensional stability. Moreover, these nanopapers also showcase the desired optical performances, including both high visible transmittance (>85%) and total ultraviolet-blocking efficiency (>91%, only transmitting a little of UVA). Overall, this fully degradable film is a promising alternative to replacing conventional plastics that are applied in multiple areas.

Preparation of Transparent Sandwich-like Superhydrophobic Coating on Glass with High Stability and Self-Cleaning Properties

High stability and transparent superhydrophobic coating on a glass substrate that can effectively repel the wetting dust as a self-cleaning property are beneficial traits for solving the decrease in optical lens clarity in an unmanned underground mining environment. However, the transparent superhydrophobic coating has still not been applied due to the contradiction between visibility, hydrophobicity and durability. Herein, a sandwich-like superhydrophobic coating was designed and prepared on borosilicate glass, which consisted of a micro/nanostructure body of neutral silicone sealant (primer) and hydrophobic silica nanoparticles (interlayer), as well as a protective layer of ultraviolet (UV) gel. The coated glass exhibited excellent superhydrophobicity towards many aqueous solutions, and had highly visible light transparency of 80% at 4 wt.% primer mass content. Furthermore, significant tests including the droplet impact, hot water boiling, stirring in acetic acid aqueous solution and sandpaper abrasion were performed on our superhydrophobic coating, which indicated that the obtained transparent coating had good stability and excellent mechanical durability. The coated glass also showed a more wonderful self-cleaning property compared with that of the original glass. This superhydrophobic coating on glass substrate, fabricated by a facile and cost-effective layer-by-layer construction approach, has great potential for general and practical application in the unmanned mining environment under multiple dust and atomized water conditions.

UV-Assisted Multiscale Superhydrophobic Wood Resisting Surface Contamination and Failure

In the modern forestry, the demand for renewable and environmentally friendly wood protection is increasing. This paper reports a green method for preparing stable and self-cleaning superhydrophobic coating for wood protection by dripping polyvinyl alcohol cross-linked hollow silica nanoparticles on the surface of wood in combination with polydimethylsiloxane modification. The coating is based on a laminated structure with layers stacked on the surface of the wood and cured quickly with the assistance of UV. The coatings obtained on wood substrates with appropriate ratios have excellent superhydrophobic properties, with an optimum water contact angle of up to 160.4 ± 0.2°. The coating also exhibits good transparency in the UV-visible spectrum and a maximum transmittance of 91%. With transmission electron microscopy, the microscopic morphology of the self-assembled hollow silica nanoparticles was observed. Scanning electron microscopy, Fourier transform infrared spectroscopy, and X-ray diffraction were also applied to investigate the morphology and chemical composition of the coatings. A water contact angle of 151.5 ± 0.7° was maintained even after the abrasion tests with sandpaper at a distance of 300 cm. Meanwhile, the resultant coatings exhibit good self-cleaning properties apart from mechanical durability and chemical stability, which enables effective resistance to contamination. Evidenced by the abovementioned data, this composite coating is capable of optimizing the surface wettability of wood, offering a new dimension to the extensive and prolonged application of wood and wood-based products. Furthermore, considering the advantages of this method, it could also be used in other areas in the future, such as glass, solar substrates, and optical devices.

Fabrication of a waterborne, superhydrophobic, self-cleaning, highly transparent and stable surface

Superhydrophobic surfaces have received tremendous attention worldwide. However, the synthesis of a superhydrophobic surface possessing two paradoxical characteristic properties - stability and transparency, is a vital aspect that has been addressed in this paper. The surface was fabricated by an environmentally friendly process, which used distilled water for the dissolution of SiO2 nanoparticles in the presence of surfactants, instead of organic solvents. Moreover, the surface was transparent and had self-cleaning properties and stability. The optimal balance of roughness and multi-porous structure imparted excellent transparency to this surface. Importantly, both the conformal coating and the SiO2 nanoparticles embedded in the half solidified conformal coating contributed to the excellent stability, thus overcoming the paradox. The surface could withstand a temperature of 150 °C for 24 h and also different temperature regimes between 0-200 °C for 2 h. In addition, this surface could resist repeated scratches and abrasion as well as strong acids and alkali. The surface achieved its self-cleaning ability due to the introduction of surfactants containing the F element. This simple but novel strategy and surface have the advantages of high safety, low cost and environmental-friendliness.

Genetical Surface Display of Silicatein on Yarrowia lipolytica Confers Living and Renewable Biosilica-Yeast Hybrid Materials

In this work, a biological engineering-based biosilica-yeast hybrid material was developed. It was obtained by the aggregation of Yarrowia lipolytica through biosilicification catalyzed using genetically displayed silicatein on its cell surface. With orthosilicate or seawater as the substrate, the silicatein-displayed yeast could aggregate into flocs with a flocculation efficiency of nearly 100%. The resulting floc was found to be a sheetlike biosilica-yeast hybrid material formed by the biosilica-mediated immobilization of yeast cells via cross-linking and embedding, turning the original hydrophilicity of yeast cells into hydrophobicity. In addition, this material was characterized to be porous with an average pore diameter of approximately 10 μm and porosity of over 70%. Because of these properties, this hybrid material could achieve enhanced removal efficiencies for chromium ions and n-hexadecane, which were both above 99%, as compared to the free cells of Y. lipolytica in aqueous environments. Importantly, this hybrid material could be recultivated to generate new batches of yeast cells that maintain parallel properties to the first generation so that the same hybrid material could be reproduced with unchanged highly efficient removal of chromium and n-hexadecane to those of the first generation, demonstrating that this biosilica-yeast hybrid material was living and renewable. This work presented a novel way of harnessing silicatein and Y. lipolytica to achieve biological synthesis of a living inorganic-organic hybrid material that has potential to be applied in water treatment.