Ultraporous superhydrophobic gas-permeable nano-layers by scalable solvent-free one-step self-assembly

Bioinspired multi-scale interface design for wet gas sensing based on rational water management

Natural organisms have evolved multi-scale wet gas sensing interfaces with optimized mass transport pathways in biological fluid environments, which sheds light on developing artificial counterparts with improved wet gas sensing abilities and practical applications. Herein, we highlighted current advances in wet gas sensing taking advantage of optimized mass transport pathways endowed by multi-scale interface design. Common moisture resistance (e.g., employing moisture resistant sensing materials, post-modifying moisture resistant coatings, physical heating for moisture resistance, and self-removing hydroxyl groups) and moisture absorption (e.g., employing moisture absorption sensing materials and post-modifying moisture absorption coatings) strategies for wet gas sensing were discussed. Then, the design principles of bioinspired multi-scale wet gas sensing interfaces were provided, including macro-level condensation mediation, micro/nano-level transport pathway adjustment and molecular level moisture-proof design. Finally, perspectives on constructing bioinspired multi-scale wet gas sensing interfaces were presented, which will not only deepen our understanding of the underlying principles, but also promote practical applications.

Prevention of uropathogenic E. coli biofilm formation by hydrophobic nanoparticle coatings on polymeric substrates

Biofilms in infections are a major health-care challenge and strategies to reduce their formation on medical devices are crucial. Fabrication of superhydrophobic coatings based on hydrocarbon adsorption on rare-earth oxides constitutes an attractive strategy, but their capacity to prevent biofilm formation has not been studied. Here, we explore a scalable and reproducible nanofabrication process for the manufacture of such superhydrophobic coatings and study their antibiofilm activity against clinically-relevant uropathogenic E. coli. These coatings reduce bacterial biofilm formation and prevent biofouling with potential applications preventing medical device related infections.

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.

Forest-like Laser-Induced Graphene Film with Ultrahigh Solar Energy Utilization Efficiency

To achieve high solar energy utilization efficiency, photothermal materials with broadband absorption of sunlight and high conversion efficiency are becoming a fast-growing research focus. Inspired by the forest structure with efficient sunlight utilization, we designed and fabricated a graphene film consisting of densely arranged porous graphene though laser scribing on polybenzoxazine resin (poly(Ph-ddm)). This hierarchical structure significantly reduced the light reflection of graphene as a 2D material. With a combination of advanced photothermal conversion properties of graphene, the 3D structured graphene film, named forest-like laser-induced graphene (forest-like LIG), was endowed with a very high light absorption of 99.0% over the whole wavelength range of sunlight as well as advanced light-to-heat conversion performance (reaching up to 87.7 °C within 30 s under the illumination of simulated sunlight and showing an equilibrium temperature of 90.7 ± 0.4 °C). As a further benefit of its superhydrophobicity, a photothermal actuator with quick actuated response and high motion velocity, as well as a solar-driven interfacial desalination membrane with durable salt-rejecting properties and high solar evaporation efficiencies, was demonstrated.

Wetting-regulated gas-involving (photo)electrocatalysis: biomimetics in energy conversion

(Photo)electrolysis of water or gases with water to species serving as industrial feedstocks and energy carriers, such as hydrogen, ammonia, ethylene, propanol, etc., has drawn tremendous attention. Moreover, these processes can often be driven by renewable energy under ambient conditions as a sustainable alternative to traditional high-temperature and high-pressure synthesis methods. In addition to the extensive studies on catalyst development, increasing attention has been paid to the regulation of gas transport/diffusion behaviors during gas-involving (photo)electrocatalytic reactions towards the goal of creating industrially viable catalytic systems with high reaction rates, excellent long-term stabilities and near-unity selectivities. Biomimetic surfaces and systems with special wetting capabilities and structural advantages can shed light on the future design of (photo)electrodes and address long-standing challenges. This article is dedicated to bridging the fields of wetting and catalysis by reviewing the cutting-edge design methodologies of both gas-evolving and gas-consuming (photo)electrocatalytic systems. We first introduce the fundamentals of various in-air/underwater wetting states and their corresponding bioinspired structural properties. The relationship amongst the bubble transport behavior, wettability, and porosity/tortuosity is also discussed. Next, the latest implementations of wetting-related design principles for gas-evolving reactions (i.e. the hydrogen evolution reaction and oxygen evolution reaction) and gas-consuming reactions (i.e. the oxygen reduction reaction and CO2 reduction reaction) are summarized. For photoelectrode designs, additional factors are taken into account, such as light absorption and the separation, transport and recombination of photoinduced electrons and holes. The influences of wettability and 3D structuring of (photo)electrodes on the catalytic activity, stability and selectivity are analyzed to reveal the underlying mechanisms. Finally, remaining questions and related future perspectives are outlined.

Multifunctional superhydrophobic adsorbents by mixed-dimensional particles assembly for polymorphic and highly efficient oil-water separation

Supra-wetting materials, especially superhydrophobic absorption materials, as an emerging advanced oil-water separation material have attracted extensive concern in the treatment of oil spillage and industrial oily wastewater. However, it is still a challenge to fabricate robust and multifunctional superhydrophobic materials for the multitasking oil-water separation and fast clean-up of the viscous crude oil by an environment-friendly and scalable method. Herein, a solid-solid phase ball-milling strategy without chemical reagent-free modification was proposed to construct heterogeneous superhydrophobic composites by using waste soot as the solid-phase superhydrophobic modifier. A series of covalent bond restricted soot-graphene (S-GN) or soot-Fe₃O₄ (S-Fe₃O₄) composite materials with a peculiar micro-nano structure are prepared. Through "glue+superhydrophobic particles" method, the prepared soot-based composite particles are facilely loaded on the porous skeleton of the sponge to obtain multifunctional superhydrophobic adsorbents. The reported superhydrophobic adsorbents exhibited robust chemical and mechanical stability, convenient magnetic collection, the high oil absorption capacity of 60-142 g g^-1, durable recyclability (>250 cycles), efficient separation efficiency (>99.5%) and outstanding self-heated performance, which enable them to be competent for oil-water separation in multitasking and complex environment (floating oils, continuous oil collection, oil-in-water emulsion, and viscous oil-spills).

Designing Re-Entrant Geometry: Construction of a Superamphiphobic Surface with Large-Sized Particles

Re-entrant geometries can effectively trap air pockets beneath coating surfaces, prevent the penetration of low surface tension organic liquids, and achieve superamphiphobic performance. However, the creation of re-entrant geometries through particle-based spray coating remains a challenge. In the past decade, various studies have focused on the preparation of superamphiphobic coatings using ultrafine nanoparticles (10-15 nm) using conventional spray-coating methods. In this work, we aim to fabricate a spray-coated superamphiphobic surface using large particles with a hierarchical structure. The study systematically investigated the wetting behaviors of liquids with different topographies obtained using large particles (i.e., smooth, micro, nano, and micro/nanostructures) by different coating methods. The findings suggested that compared with the typical colloid template method, the surface obtained using the spray-coating method showed much greater roughness, which greatly enhanced the oleophobicity of the coating. Furthermore, only hierarchically monodisperse hollow SiO₂ spheres (MDH-SiO₂) showed excellent superamphiphobicity, which was independent of the hollow sphere size. While maintaining the coating roughness, by applying solid C@SiO₂ as a reference sample, the important role of the hollow structure of MDH-SiO₂ at the solid-liquid-air interface was confirmed. Nanosphere-surrounded hollow structures were shown to serve as a re-entrant type structure, preventing the imbibition of the liquid, finally leading to a stable Cassie state. This design strategy may provide useful guidelines for the fabrication of large particle-based spray-coated superamphiphobic surfaces.

A femtosecond laser-induced superhygrophobic surface: beyond superhydrophobicity and repelling various complex liquids

Surfaces that can strongly repel various complex liquids, not just pure water, are highly desirable and the fabrication of such surfaces still remains a huge challenge because the liquids one wants to repel usually have a complex chemical composition, viscosity, and concentration. Here, a superhygrophobic surface microstructure was created on a polytetrafluoroethylene (PTFE) surface by femtosecond laser treatment. The laser-ablated surface was composed of a micro/nanoscale hierarchical structure and micropores with a certain degree of re-entrant curvature. After femtosecond laser ablation, the sample surface is directly endowed with superhygrophobicity and has great ability to repel various pure and complex liquids, such as water, 10 000 ppm bovine serum albumin, cola, 10 000 ppm glucose, juice, and saline. It is because the combined effect of the ultralow surface energy of the PTFE material, the laser-induced hierarchical rough microstructure, and the partly re-entrant surface curvature of the porous structure allows the complex liquid droplets to be at the robust Cassie state on the laser-induced surface microstructure. Such superhygrophobic surfaces can be potentially applied in cell engineering, medical instruments, food packaging, microfluidics technology, chemical engineering, and so on.

TDI/TiO2 Hybrid Networks for Superhydrophobic Coatings with Superior UV Durability and Cation Adsorption Functionality

Durability under UV illumination remains a big challenge of TiO₂-based superhydrophobic coatings, with the photocatalytic effect causing degradation of low-surface-energy material over time, resulting in the surfaces losing their hydrophobicity. We report surfaces made from tolylene-2,4-diisocyanate (TDI)/TiO₂ hybrid networks that demonstrate superhydrophobicity and superior UV durability. Structural and morphological studies reveal that the TDI/TiO₂ hybrid networks are composed of TiO₂ nanoparticles interconnected with TDI bridges and then encapsulated by a TDI layer. Through controlling the fraction of TDI in the synthesis process, the thickness of the TDI encapsulation layer around the TDI/TiO₂ hybrid networks can be varied. When the weight ratio of TDI/TiO₂ is 5:1, the superhydrophobicity of the hybrid network surface remains almost unchanged after a month of continuous UV illumination. This hybrid network surface can also clean methylene blue solution through the synergistic effects of cation adsorption and photocatalysis, holding promising potential for applications toward reducing cation pollutions in both liquid and air environments.

Environmentally durable superhydrophobic surfaces with robust photocatalytic self-cleaning and self-healing properties prepared via versatile film deposition methods

Superhydrophobic (SH) surfaces with self-cleaning photocatalytic properties have become an important research focus in recent years. In this work, we fabricated multifunctional and environmentally durable SH surfaces via a facile one-step reaction of octadecyl isocyanate (ODI) with TiO₂ particles. The resulting films possess SH properties, facilitated by a combination of hydrophobic long alkyl chains and the hierarchical crystalline structure. Films can be prepared via spray or blade coating on a variety of hard and soft substrates, and function well when exposed to either air or oil. The coating retains its SH properties for at least 6 months in ambient conditions, and after organic pollution it can recover its SH properties using UV or sun light illumination. After water impalement, the SH properties can self-heal via the self-assembly of long alkyl chains to their original state within several hours at ambient conditions, or within minutes on a heating stage. The covalent bonds between alkyl chains and TiO₂, together with hydrogen bonds between adjacent alkyl chains, greatly increased the surface durability of the SH films. This multifunctional SH coating is a very promising material for commercial and industrial coating applications.

RMS roughness-independent tuning of surface wettability by tailoring silver nanoparticles with a fluorocarbon plasma polymer

A layer of 14 nm-sized Ag nanoparticles undergoes complex transformation when overcoated by thin films of a fluorocarbon plasma polymer. Two regimes of surface evolution are identified, both with invariable RMS roughness. In the early regime, the plasma polymer penetrates between and beneath the nanoparticles, raising them above the substrate and maintaining the multivalued character of the surface roughness. The growth (β) and the dynamic (1/z) exponents are close to zero and the interface bears the features of self-affinity. The presence of inter-particle voids leads to heterogeneous wetting with an apparent water contact angle θ_a = 135°. The multivalued nanotopography results in two possible positions for the water droplet meniscus, yet strong water adhesion indicates that the meniscus is located at the lower part of the spherical nanofeatures. In the late regime, the inter-particle voids become filled and the interface acquires a single valued character. The plasma polymer proceeds to grow on the thus-roughened surface whereas the nanoparticles keep emerging away from the substrate. The RMS roughness remains invariable and lateral correlations propagate with 1/z = 0.27. The surface features multiaffinity which is given by different evolution of length scales associated with the nanoparticles and with the plasma polymer. The wettability turns to the homogeneous wetting state.

Omnidirectional Self-Assembly of Transparent Superoleophobic Nanotextures

Engineering surface textures that are highly transparent and repel water, oil, and other low surface energy fluids can transform our interaction with wet environments. Despite extensive progress, current top-down methods are based on directional line-of-sight fabrication mechanisms that are limited by scale and cannot be applied to highly uneven, curved, and enclosed surfaces, while bottom-up techniques often suffer from poor optical transparency. Here, we present an approach that enables the rapid, omnidirectional synthesis of flexible and up to 99.97% transparent superhydrophobic and -oleophobic textures on many variable surface types. These features are obtained by the spontaneous formation of a multi re-entrant morphology during the controlled self-assembly of nanoparticle aerosols. We also develop a mathematical model to explain and control the self-assembly dynamics, providing important insights for the rational engineering of functional materials. We envision that our findings represent a significant advance in imparting superoleophobicity and superamphiphobicity to a so-far inapplicable family of materials and geometries for multifunctional applications.

A superhydrophobic solar selective absorber used in a flat plate solar collector

A new kind of superhydrophobic (SH) solar selective absorber (SSA) used in a low-temperature flat plate solar collector is proposed.

Ultra-Durable and Transparent Self-Cleaning Surfaces by Large-Scale Self-Assembly of Hierarchical Interpenetrated Polymer Networks

In nature, durable self-cleaning surfaces such as the Lotus leaf rely on the multiscale architecture and cohesive regenerative properties of organic tissue. Real-world impact of synthetic replicas has been limited by the poor mechanical and chemical stability of the ultrafine hierarchical textures required for attaining a highly dewetting superhydrophobic state. Here, we present the low-cost synthesis of large-scale ultradurable superhydrophobic coatings by rapid template-free micronano texturing of interpenetrated polymer networks (IPNs). A highly transparent texture of soft yielding marshmallow-like pillars with an ultralow surface energy is obtained by sequential spraying of a novel polyurethane-acrylic colloidal suspension and a superhydrophobic nanoparticle solution. The resulting coatings demonstrate outstanding antiabrasion resistance, maintaining superhydrophobic water contact angles and a pristine lotus effect with sliding angles of below 10° for up to 120 continuous abrasion cycles. Furthermore, they also have excellent chemical- and photostability, preserving the initial performance upon more than 50 h exposure to intense UVC light (254 nm, 3.3 mW cm(-2)), 24 h of oil contamination, and highly acidic conditions (1 M HCl). This sprayable polyurethane-acrylic colloidal suspension and surface texture provide a rapid and low-cost approach for the substrate-independent fabrication of ultradurable transparent self-cleaning surfaces with superior abrasion, chemical, and UV-resistance.

Engineering polydimethylsiloxane with two-dimensional graphene oxide for an extremely durable superhydrophobic fabric coating

A type of nanostructured material comprising reduced graphene oxide (RGO) modified polydimethylsiloxane (PDMS) for fabric coating is described.