Lubricant‐Infused Nanoparticulate Coatings Assembled by Layer‐by‐Layer Deposition

Omniphobic coatings are designed to repel a wide range of liquids without leaving stains on the surface. A practical coating should exhibit stable repellency, show no interference with color or transparency of the underlying substrate and, ideally, be deposited in a simple process on arbitrarily shaped surfaces. We use layer‐by‐layer (LbL) deposition of negatively charged silica nanoparticles and positively charged polyelectrolytes to create nanoscale surface structures that are further surface‐functionalized with fluorinated silanes and infiltrated with fluorinated oil, forming a smooth, highly repellent coating on surfaces of different materials and shapes. We show that four or more LbL cycles introduce sufficient surface roughness to effectively immobilize the lubricant into the nanoporous coating and provide a stable liquid interface that repels water, low‐surface‐tension liquids and complex fluids. The absence of hierarchical structures and the small size of the silica nanoparticles enables complete transparency of the coating, with light transmittance exceeding that of normal glass. The coating is mechanically robust, maintains its repellency after exposure to continuous flow for several days and prevents adsorption of streptavidin as a model protein. The LbL process is conceptually simple, of low cost, environmentally benign, scalable, automatable and therefore may present an efficient synthetic route to non‐fouling materials.     

On‐Demand Liquid Transportation Using Bioinspired Omniphobic Lubricated Surfaces Based on Self‐Organized Honeycomb and Pincushion Films

In this work, on‐demand control of liquids is realized by using elastic, patterned omniphobic surfaces. This paves the way for novel microfluidics, as well as liquid harvesting, transportation, and manipulation technologies. Inspired by the lubricating properties of pitcher plants, microstructured 1,2‐polybutadiene honeycomb and pincushion films obtained by self‐organization are fluorinated by the ene‐thiol reaction and infused with fluorinated lubricant to obtain omniphobic liquid‐repellent surfaces. Unlike conventional bioinspired omniphobic surfaces, the liquid repellency of the fabricated surface can be programmed by changing the surface microstructures via patterning of the film. Furthermore, the elasticity of the omniphobic film is suitable for controlling the repellency through external stimuli. The method presented here for the fabrication of lubricant‐infused omniphobic microstructured surfaces is also simple, cost‐effective, and can be scaled for large area fabrication.     

A universal roll‐to‐roll slot‐die coating approach towards high‐efficiency organic photovoltaics

This work develops a combinational use of solvent additive and in‐line drying oven on the flexible organic photovoltaics to improve large‐area roll‐to‐roll (R2R) slot‐die coating process. Herein, addition of 1,8‐diiodooctane (DIO) in the photoactive layer is conducted to yield a performance of 3.05% based on the blending of poly(3‐hexylthiophene) (P3HT) and [6,6]‐phenyl C₆₁‐butyric acid methyl ester (PC₆₁BM), and a very promising device performance of 7.32% based on the blending of poly[[4,8‐bis[(2‐ethylhexyl)oxy] benzo[1,2‐b:4,5‐b’] dithiophene‐2,6‐diyl] [3‐fluoro‐2‐[(2‐ethylhexyl)carbonyl]thieno[3,4‐b]thiophenediyl]] (PTB7) and [6,6]‐phenyl C₇₁‐butyric acid methyl ester (PC₇₁BM). Based on this R2R slot‐die coating approach for various polymers, we demonstrate the high‐performance result with respect to the up‐scaling from small high‐PCE cell to large‐area module. This present study provides a route for fabricating a low‐cost, large‐area, and environmental‐friendly flexible organic photovoltaics.     

High Performance Roll‐to‐Roll Produced Fullerene‐Free Organic Photovoltaic Devices via Temperature‐Controlled Slot Die Coating

Solution‐processed organic photovoltaics (OPVs) have continued to show their potential as a low‐cost power generation technology; however, there has been a significant gap between device efficiencies fabricated with lab‐scale techniques—i.e., spin coating—and scalable deposition methods. Herein, temperature‐controlled slot die deposition is developed for the photoactive layer of OPVs. The influence of solution and substrate temperatures on photoactive films and their effects on power conversion efficiency (PCE) in slot die coated OPVs using a 3D printer‐based slot die coater are studied on the basis of device performance, molecular structure, film morphology, and carrier transport behavior. These studies clearly demonstrate that both substrate and solution temperatures during slot die coating can influence device performance, and the combination of hot substrate (120 °C) and hot solution (90 °C) conditions result in mechanically robust films with PCE values up to 10.0% using this scalable deposition method in air. The efficiency is close to that of state‐of‐the‐art devices fabricated by spin coating. The deposition condition is translated to roll‐to‐roll processing without further modification and results in flexible OPVs with PCE values above 7%. The results underscore the promising potential of temperature‐controlled slot die coating for roll‐to‐roll manufacturing of high performance OPVs.     

Integration of Self‐Lubrication and Near‐Infrared Photothermogenesis for Excellent Anti‐Icing/Deicing Performance

The economic and safety issues caused by ice accretion have become more and more serious. Except for traditional ways of anti‐icing, such as spraying agents, mechanical/thermal removal, etc., more economic approaches are urgently required. This work demonstrates the conceptual feasibility of using a self‐lubricated photothermal coating for both anti‐icing and deicing function. The coating is generally water repellent and infiltrated with hydrocarbon or perfluorocarbon oils as the lubricant to endow a liquid interface for preventing ice accumulation and minimizing the adhesion of ice on surfaces once it is formed. Fe₃O₄ nanoparticles are added to the film to afford high efficiency photothermal effect under near‐infrared irradiation for rapidly melting the accumulated ice. The conceptual strategy can be easily implemented as a facile method to fabricate analogous sprayed coatings. It represents a major advance to tackle the challenging icing issue that is normally seen as a disaster in everyday life.     

Filefish‐Inspired Surface Design for Anisotropic Underwater Oleophobicity

Surfaces with anisotropic wettability, widely found in nature, have inspired the development of one‐dimensional water control on surfaces relying on the well‐arranged surface features. Controlling the wetting behavior of organic liquids, especially the motion of oil fluid on surfaces, is of great importance for a broad range of applications including oil transportation, oil‐repellent coatings, and water/oil separation. However, anisotropic oil‐wetting surfaces remain unexplored. Here, the unique skin of a filefish Navodon septentrionalis shows anisotropic oleophobicity under water. On the rough skin of N. septentrionalis, oil droplets tend to roll off in a head‐to‐tail direction, but pin in the opposite direction. This pronounced wetting anisotropy results from the oriented hook‐like spines arrayed on the fish skin. It inspires further exploration of the artificial anisotropic underwater oleophobic surfaces: By mimicking the oriented hook‐like microstructure on a polydimethylsiloxane layer via soft lithography and subsequent oxygen‐plasma treatment to make the PDMS hydrophilic, artificial fish skin is fabricated which has similar anisotropic underwater oleophobicity. Drawn from the processing of artificial fish skin, a simple principle is proposed to achieve anisotropic underwater oleophobicity by adjusting the hydrophilicity of surface composition and the anisotropic microtextures. This principle can guide the simple mass manufacturing of various inexpensive high surface‐energy materials, and the principle is demonstrated on commercial cloth corduroy. This study will profit broad applications involving low‐energy, low‐expense oil transportation, underwater oil collection, and oil‐repellant coatings on ship hulls and oil pipelines.     

Polycationic Synergistic Antibacterial Agents with Multiple Functional Components for Efficient Anti‐Infective Therapy

Multifunctional antibacterial photodynamic therapy is a promising method to combat regular and multidrug‐resistant bacteria. In this work, eosin Y (EY)‐based antibacterial polycations (EY‐QEGED? R, R = ? CH₃ or ? C₆H₁₃) with versatile types of functional components including quaternary ammonium, photosensitizer, primary amine, and hydroxyl species are readily synthesized based on simple ring‐opening reactions. In the presence of light irradiation, such antibacterial polymers exhibit high antibacterial efficiency against both Escherichia coli and Staphylococcus aureus. In particular, EY‐QEGED? R elicits a remarkable synergistic antibacterial activity owing to the combined photodynamic and quaternary ammonium antibacterial effects. Due to its rich primary amine groups, EY‐QEGED? R also can be readily coated on different substrates, such as glass slides and nonwoven fabrics via an adhesive layer of polydopamine. The resultant surface coating of EY‐QEGED? CH₃ (s‐EY‐QEGED? CH₃) produces excellent in vitro antibacterial efficacy. The plentiful hydroxyl groups impart s‐EY‐QEGED? CH₃ with potential antifouling capability against dead bacteria. The antibacterial polymer coatings also demonstrate low cytotoxicity and good hemocompatibility. More importantly, s‐EY‐QEGED? CH₃ significantly enhances in vivo therapeutic effects on an infected rat model. The present work provides an efficient strategy for the rational design of high‐performance antibacterial materials to fight biomedical device‐associated infections.     

High‐Temperature Performance of Alumina–Zirconia Composite Coatings Containing Amorphous Phases

Amorphous phases are commonly found in nanostructured plasma‐sprayed coatings. Nonetheless, the role of these phases in the resulting coatings’ properties has remained uninvestigated until now. In the present work, pseudo‐eutectic coatings—based on alumina and 8 wt% yttria‐stabilized zirconia (YSZ)—containing amorphous phases are produced using a suspension‐plasma‐spray process. These composite materials are a potential choice for thermal‐barrier coating applications. The role of the amorphous phase on the performance of the coatings is investigated before and after heat treatment. Results show that, although the amorphous phases in untreated coatings reduce the thermal conductivity, they impair the mechanical properties. However, treatment above the crystallization temperature leads to better mechanical properties as well as enhanced high‐temperature stability of the resulting nanostructure. Moreover, the role of alumina as a stabilizer of high‐temperature YSZ phases (tetragonal and cubic) is confirmed and the high‐temperature phase stability of the alumina–YSZ composite is demonstrated. The amorphous phases are found to crystallize into their corresponding high‐temperature stable phases; i. e., α‐alumina and tetragonal zirconia.     

Temperature-Triggered Dynamic Janus Fabrics for Smart Directional Water Transport

In this study, thermosensitive amino-silica@PDVB/PNIPAM Janus particles (JPs) are synthesized by seed emulsion polymerization-induced phase separation and selective modification methods. Amino-modified silica moieties are covalently bonded to a diverse choice of substrates to achieve robust composite coatings, and a PDVB/PNIPAM abdomen forms a micro-nano-scale hierarchical surface. PNIPAM has a lower critical solution temperature (LCST), which allows the hydrophilic and hydrophobic properties of the coating to reverse with a change in temperature. When the fabrics are coated with the thermosensitive Janus particles, water repellency is observed above 32 °C, while hydrophilicity is revealed below 32 °C. Then, after the composite fabric is worn, the side next to the skin becomes hydrophobic due to the high temperature, and the side facing the environment is hydrophilic. Therefore, sweat can be pumped from the hydrophobic side to the hydrophilic side through the dynamic Janus fabric. The dynamic hydrophobic–hydrophilic Janus structure enables the efficient and fast evaporation of sweat. The perspiration rate of Janus fabrics is five times higher than that of commercial cotton fabrics. While the wettability of the composite coating remains reversible after 20 temperature cycles and 20 tape adhesion cycles, showing good mechanical durability. The reversible thermal sensitivity remains after repeated rubbing and ultrasonic immersion.     

Novel Brush Polymers with Phosphorylcholine Bristle Ends: Synthesis,Structure, Properties,and Biocompatibility

N ew brush polymers with various numbers of bristle ends incorporating phosphorylcholine (PC) moieties are synthesized. The polymers are thermally stable up to 175 °C and form good‐quality films with conventional spin‐, roll‐, and dip‐coating, and subsequent drying processes. Interestingly, all these brush polymers, as a PC‐containing polymer, demonstrate a stable molecular multi‐bilayer structure in thin films that arise due to the efficient self‐assembly of the bristles for temperatures <55 °C and PC‐rich surfaces, and therefore successfully mimic natural cell‐membrane surfaces. These brush‐polymer films exhibit excellent water wettability and water sorption whilst retaining the remarkable molecular multi‐bilayer structure, and thus have hydrophilic surfaces. These novel multi‐bilayer structured films repel fibrinogen molecules and platelets from their surfaces but also have bactericidal effects on bacteria. Moreover, the brush‐polymer films are found to provide comfortable surface environments for the successful anchoring and growth of HEp‐2 cells, and to exhibit excellent biocompatibility in mice. These newly developed brush polymers are suitable for use in biomedical applications including medical devices and biosensors that require biocompatibility and the reduced possibility of post‐operative infection.     

Robust,Self‐Healing Superamphiphobic Fabrics Prepared by Two‐Step Coating of Fluoro‐Containing Polymer,Fluoroalkyl Silane,and Modified Silica Nanoparticles

A robust, superamphiphobic fabric with a novel self‐healing ability to autorepair from chemical damage is prepared by a two‐step wet‐chemistry coating technique using an easily available material system consisting of poly(vinylidene fluoride‐co‐hexafluoropropylene), fluoroalkyl silane, and modified silica nanoparticles. The coated fabrics can withstand at least 600 cycles of standard laundry and 8000 cycles of abrasion without apparently changing the superamphiphobicity. The coating is also very stable to strong acid/base, ozone, and boiling treatments. After being damaged chemically, the coating can restore its super liquid‐repellent properties by a short‐time heating treatment or room temperature ageing. This simple but novel and effective coating system may be useful for the development of robust protective clothing for various applications.     

Bioinspired Ribbed Nanoneedles with Robust Superhydrophobicity

The robustness of superhydrophobicity is a fundamental issue for the applications of water‐repellent materials. Inspired by the hierarchical structures of water‐strider legs, this work describes a new water‐repellent material decorated with ribbed, conical nanoneedles, successfully achieved on the surface of copper and consisting of copper hydroxide nanoneedle arrays sculptured with nanogrooves. The behavior of water drops on an as‐prepared surface under various external disturbances is investigated. It is shown in particular that squeezing and relaxing drops between two such surfaces leads to a fully reversible exploration of the solid surface by the liquid, which is distinct from other superhydrophobic surfaces. This unique character is attributed to the penetrating Cassie state that occurs at the ribbed, conical nanoneedles. The proprietary lateral nanogrooves can, not only vigorously support the enwrapped liquid‐air interface when a force is applied to the drop, but also provide reliable contact lines for the easy de‐pinning of the deformed interface when the force is released from the drop. The results confirm the exceptional ability of strider legs to repel water, and should help to further the design of robust water‐repellent materials and miniaturized aquatic devices.     

Molecular Sieving on the Surface of a Protein Provides Protection Without Loss of Activity

Tethering polymers to surfaces represents the cornerstone of a wide range of applications, including the stabilization of colloids/biomolecules and the preparation of functional coatings. Unfortunately, despite the prevalence of protein‐tethered polymers in the pharmaceutical sector, the analysis of such polymer monolayers on a molecular level is difficult. In this work, simple ¹H NMR spectroscopy and the catalytic properties of α‐chymotrypsin are used to analyze the conformational/permeability properties of protein‐bound monolayers of poly(oligoethyleneglycol monomethylether methacrylate) (pOEGMA), a biocompatible comb‐polymer of interest in the biomedical field. By analyzing >100 distinct conjugates of α‐chymotrypsin and pOEGMA, a detailed picture of the behavior of pOEGMA on the surface of a protein was obtained. Remarkably, control of polymer conformation and inter‐penetration produced a thus far overlooked molecular sieving effect. The application of this effect for the “smart” PEGylation of proteins is portrayed, from which insight is provided for the design of other therapeutic bioconjugates and functional coatings with selective permeability properties.     

Mechanical Properties of Highly Porous Super Liquid‐Repellent Surfaces

Surfaces with self‐cleaning properties are desirable for many applications. Conceptually, super liquid‐repellent surfaces are required to be highly porous on the nano‐ or micrometer scale, which inherently makes them mechanically weak. Optimizing the balance of mechanical strength and liquid repellency is a core aspect toward applications. However, quantitative mechanical testing of porous, super liquid‐repellent surfaces is challenging due to their high surface roughness at different length scales and low stress tolerance. For this reason, mechanical testing is often performed qualitatively. Here, the mechanical responses of soot‐templated super liquid‐repellent surfaces are studied qualitatively by pencil and finger scratching and quantitatively by atomic force microscopy, colloidal probe force measurements, and nanoindentation. In particular, colloidal probe force measurements cover the relevant force and length scales. The effective elastic modulus, the plastic work W_plastic and the effective adhesive work W_adhesive are quantified. By combining quantitative information from force measurements with measurements of surface wetting properties, it is shown that mechanical strength can be balanced against low wettability by tuning the reaction parameters.     

A Simple,One‐Step Approach to Durable and Robust Superhydrophobic Textiles

Superhydrophobic textile fabrics are prepared by a simple, one‐step gas phase coating procedure by which a layer of polymethylsilsesquioxane nanofilaments is grown onto the individual textile fibers. A total of 11 textile fabrics made from natural and man made fibers are successfully coated and their superhydrophobic properties evaluated by the water shedding angle technique. A thorough investigation of the commercially relevant poly(ethylene terephthalate) fabric reveals an unparalleled long‐term water resistance and stability of the superhydrophobic effect. Because of the special surface geometry generated by the nanoscopic, fibrous coating on the microscopic, fibrous textiles, the coated fabric remains completely dry even after two months of full immersion in water and stays superhydrophobic even after continuous rubbing with a skin simulating friction partner under significant load. Furthermore, important textile parameters such as tensile strength, color, and haptics are unaffected by the silicone nanofilament coating. For the first time, an in‐depth characterization of the wetting properties, beyond simple contact angle measurements, as well as a thorough evaluation of the most important textile parameters is performed on a superhydrophobic fabric, which reveals a true potential for application.     

In Situ Self‐Assembled Polyoxotitanate Cages on Flexible Cellulosic Substrates: Multifunctional Coating for Hydrophobic,Antibacterial, and UV‐Blocking Applications

Surface coating is a powerful approach to fabricate multifunctional materials that are essential for numerous applications. However, to achieve such multifunctional coating with a facile single‐step procedure, especially on flexible substrates, is still a big challenge, as current fabrication protocols usually require sophisticated equipment and complicated procedures. Here, a novel coating technology involving in situ self‐assembly of the polyoxotitanate (POT) cage [Ti₁₈Mn₄O₃₀(OEt)₂₀Phen₃] is reported to fabricate multifunctional cotton fabrics in a single step. The in situ generated spherical microparticles of 0.8 µm average diameter are firmly mounted on the underlying cotton substrate, imparting the coated surface with robust hydrophobicity (water contact angle of 148.1 ± 5.4°), antibacterial activity (against Escherichia coli, Staphylococcus epidermidis, and Staphylococcus aureus), and excellent UV‐blocking performance (89% blocked at 350 nm). This coating technology is efficient, straightforward, requires no specialized equipment, and most importantly, is readily extendable to other flexible substrates. Combined with the rapidly developing area of POT cages and similar molecular materials, the reported technology based on in situ self‐assembly holds great promise for further advancing the fabrication of multifunctional flexible devices via a single‐step coating operation.     

Photoswitchable Superabsorbency Based on Nanocellulose Aerogels

Chemical vapor deposition of a thin titanium dioxide (TiO₂) film on lightweight native nanocellulose aerogels offers a novel type of functional material that shows photoswitching between water‐superabsorbent and water‐repellent states. Cellulose nanofibrils (diameters in the range of 5–20 nm) with native crystalline internal structures are topical due to their attractive mechanical properties, and they have become relevant for applications due to the recent progress in the methods of their preparation. Highly porous, nanocellulose aerogels are here first formed by freeze‐drying from the corresponding aqueous gels. Well‐defined, nearly conformal TiO₂ coatings with thicknesses of about 7 nm are prepared by chemical vapor deposition on the aerogel skeleton. Weighing shows that such TiO₂‐coated aerogel specimens essentially do not absorb water upon immersion, which is also evidenced by a high contact angle for water of 140° on the surface. Upon UV illumination, they absorb water 16 times their own weight and show a vanishing contact angle on the surface, allowing them to be denoted as superabsorbents. Recovery of the original absorption and wetting properties occurs upon storage in the dark. That the cellulose nanofibrils spontaneously aggregate into porous sheets of different length scales during freeze‐drying is relevant: in the water‐repellent state they may stabilize air pockets, as evidenced by a high contact angle, in the superabsorbent state they facilitate rapid water‐spreading into the aerogel cavities by capillary effects. The TiO₂‐coated nanocellulose aerogels also show photo‐oxidative decomposition, i.e., photocatalytic activity, which, in combination with the porous structure, is interesting for applications such as water purification. It is expected that the present dynamic, externally controlled, organic/inorganic aerogels will open technically relevant approaches for various applications.     

A Universal Coating Strategy for Controllable Functionalized Polymer Surfaces

Development of a universal and stable surface coating, irrespective of surface chemistry or material characteristics, is highly desirable but has proved to be extremely challenging. Conventional coating strategies including the commonly used catechol surface coating are limited to either a certain type of substrates or weak and unreliable surface bonding. Here, a simple, robust, and universal surface coating method capable for attaching any stimuli‐responsive glycidyl methacrylate (GMA)‐based copolymer, consisting of one surface‐adhesive moiety of epoxy groups and one stimuli‐responsive moiety, to any type of hydrophobic and hydrophilic surfaces via a one‐step ring‐opening reaction is proposed and demonstrated. The resultant GMA‐based copolymers are not only strongly adhered on different substrates (e.g., silicon, polypropylene, polyvinyl chloride, indium tin oxide, polyethylene terephthalate, aluminum, glass, polydimethylsiloxane, and even polyvinylidene fluoride with low surface energy), but also are possessed distinct thermal‐, pH‐, and salt‐responsive functions of bacterial killing, bacterial releasing, tunable multicolor fluorescence emission, and heavy metal detection. This coating method is also compatible with the directional quaternization of GMA‐based copolymers for further improving surface adhesion and functionality. This study provides a simple yet universal coating method to solve the long‐standing challenge of robust integration of stimuli‐responsive polymers with strong adhesion between various polymers and substrates.     

A Waterborne Coating System for Preparing Robust,Self‐healing,Superamphiphobic Surfaces

Existing coating systems for preparing superamphiphobic surfaces are predominantly confined to small‐scale uses due to the heavy use of organic solvents. Waterborne coating treatment is highly desirable for the high safety, low cost, and nonenvironmental impact, but it remains difficult to develop due to the problems in forming durable, homogeneous coating from an aqueous dispersion of amphiphobic substances. In this study, the authors have proved that lyophobic nanoparticles, fluorinated alkyl silane (FAS), and fluorocarbon surfactant can form a stable dispersion in water, suitable for preparing durable superamphiphobic surfaces on various solid substrates. A series of substrates including fabrics, sponge, wood, glass, and metal, after being coated with this ternary coating system, shows superamphiphobicity with low contact angle hysteresis. The coating is durable enough against physical abrasion, repeated washing, boiling in water, and strong acid/base attacks. Benefiting from FAS, the coating also has a self‐healing ability against both physical and chemical damages. The unexpected stability of the ternary dispersion is a result of the synergistic interaction of the three ingredients. Results from this study may promote the wide development of safe and cost‐efficient superamphiphobic techniques for diverse applications.     

Toward high‐efficiency dye‐sensitized solar cells with a photoanode fabricated via a simple water‐based formulation

An aqueous formulation containing commercially available P25 nanoparticles and a water‐soluble precursor—titanium (IV) bis(ammonium lactato)dihydroxide (TALH) has been developed and optimized for fabricating photoanodes in dye‐sensitized solar cells. An optimal formulation achieved a power conversion efficiency of 9.2%. Solar cell performance is significantly influenced by precursor concentration impacting the porosity and electron transport of the thin film. The use of TALH during processing is shown to enhance the electron transport in the resulting titanium dioxide nanoparticle network using transient decay measurements. Bridging between neighboring nanoparticles is confirmed using transmission electron microscopy explaining the enhanced electron transport. The developed formulation has several advantages, as it is water‐based, composed of inexpensive, non‐hazardous components, is easy to make, and does not require special handling. The formulation has great potential for industrial applications, in particular for DSC manufacturing using roll‐to‐roll technology. Copyright © 2014 John Wiley & Sons, Ltd.