Red phosphorus decorated electrospun carbon anodes for high efficiency lithium ion batteries.

Electrospinning is a powerful and versatile technique to produce efficient, specifically tailored and high-added value anodes for lithium ion batteries. Indeed, electrospun carbon nanofibers (CNFs) provide faster intercalation kinetics, shorter diffusion paths for ions/electrons transport and a larger number of lithium insertion sites with respect to commonly employed powder materials. With a view to further enhance battery performances, red phosphorous (RP) is considered one of the most promising materials that can be used in association with CNFs. RP/CNFs smart combinations can be exploited to overcome RP low conductivity and large volume expansion during cycling. In this context, we suggest a simple and cost effective double-step procedure to obtain high-capacity CNFs anodes and to enhance their electrochemical performances with the insertion of red phosphorous in the matrix. We propose a simple dropcasting method to confine micro- and nanosized RP particles within electrospun CNFs, thus obtaining a highly efficient, self-standing, binder-free anode. Phosphorous decorated carbon mats are characterized morphologically and tested in lithium ion batteries. Results obtained demonstrate that the reversible specific capacity and the rate capability of the obtained composite anodes is significantly improved with respect to the electrospun carbon mat alone.

Crosslinked Poly(N-Isopropylacrylamide)-Based Microfibers as Cell Manipulation Materials with Prompt Cell Detachment.

Stimuli-responsive smart materials are a key to the realization of next-generation medical technologies. Among them, the temperature-responsive polymer poly(N-isopropylacrylamide) (PNIPAAm) is attracting particular attention because it is easy to use in physiological conditions. PNIPAAm-grafted surfaces can undergo temperature-modulated cell adhesion and detachment without proteolytic enzymes, and can be used as cell-separating materials through selective cell adhesion/detachment. However, cell detachment at reduced temperatures is problematic because it takes several hours. A novel thermoresponsive crosslinked microfiber system that can greatly reduce the cell detachment time is introduced in this study. The crosslinked fibers provide temperature-dependent volume change, and enable cell detachment within 10 min of reducing the temperature, which is one-sixth of the time required in previous studies. The prompt cell detachment is thought to arise from a completely new mechanism derived from fiber swelling. This system will make a significant contribution as a novel cell manipulating system for next-generation medical technology.

Capacitive Pressure Sensor with Wide-Range, Bendable, and High Sensitivity Based on the Bionic Komochi Konbu Structure and Cu/Ni Nanofiber Network.

High-performance flexible pressure sensors have an essential application in many fields such as human detection and human-computer interaction. Herein, on the basis of the dielectric layer of a bionic komochi konbu structure, we propose a low-cost and novel capacitive sensor that achieves high sensitivity and stability over a broad range of tactile pressures. Further, the flexible and durable electrode layer of the transparent junctionless copper/nickel-nanonetwork was prepared based on electrospinning and electroless deposition techniques, which ensured high bending stability and high cycle stability of our sensor. More importantly, because of the sizeable protruding structure and internal micropores in the elastomer structure we designed, the inward curling of the protruding structure and the effectual closing of the micropores increase the effective dielectric constant under the action of the compressive force, improving the sensitivity of the sensor. Measured response and relaxation time (162 ms) are 250 times faster than those of a conventional flat polydimethylsiloxane capacitive sensor. In addition, the fabricated capacitive pressure sensor demonstrates the ability to be used on wearable applications, not only to quickly recognize the tapping and bending of a finger but also to show that the pressure of the finger can be sensed when the finger grabs the object. The sensors we have developed have shown great promise in practical applications, such as human rehabilitation and exercise monitoring, as well as human-computer interaction control.

Adsorption-Desorption Control of Fibronectin in Real Time at the Liquid/Polymer Interface on a Quartz Crystal Microbalance by Thermoresponsivity.

The cell manipulation technique using thermoresponsive polymers is currently attracting much attention for applications in the medical field. To achieve arbitrary and accurate cell control, it is necessary to intensely research fibronectin behavior. A smart surface, which has thermoresponsive wettability and which can adsorb or desorb fibronectin repeatedly without the presence of cells, was fabricated by an electrospinning method. The fabricated coating changed its structure as the temperature was changed, and this transformation could substitute for the pulling force generated by the cytoskeletal contraction of cells. Moreover, a coated quartz crystal microbalance was able to detect the fibronectin behavior as frequency shifts, which could be used in the estimation of the mass shift with the aid of suitable equations. This coating and measurement system can contribute greatly not only to the development in the medical field centered on biomaterial manipulation technologies, but also to the improvement of medical instruments.

Bionic Fish-Scale Surface Structures Fabricated via Air/Water Interface for Flexible and Ultrasensitive Pressure Sensors.

In recent years, wearable and flexible sensors have attracted considerable research interest and effort owing to their broad application prospects in wearable devices, robotics, health monitoring, and so on. High-sensitivity and low-cost pressure sensors are the primary requirement in practical application. Herein, a convenient and low-cost process to fabricate a bionic fish-scale structure poly(dimethylsiloxane) (PDMS) film via air/water interfacial formation technique is presented. High-sensitivity flexible pressure sensors can be constructed by assembling conductive films of graphene nanosheets into a microstructured film. Thanks to the unique fish-scale structures of PDMS films, the prepared pressure sensor shows excellent performance with high sensitivity (-70.86% kPa-1). In addition, our pressure sensors can detect weak signals, such as wrist pulses, respiration, and voice vibrations. Moreover, the whole process of pressure sensor preparation is cost-effective, eco-friendly, and controllable. The results indicate that the prepared pressure sensor has a profitable and efficient advantage in future applications for monitoring human physiological signals and sensing subtle touch, which may broaden its potential applications in wearable devices.

Heat-Shielding and Self-Cleaning Smart Windows: Near-Infrared Reflective Photonic Crystals with Self-Healing Omniphobicity via Layer-by-Layer Self-Assembly.

Bioinspired photonic crystals that can be used to precisely control the optical reflection of light of a specific wavelength by varying their thickness and refractive index have attracted much attention. Among them, photonic crystals that can reflect near-infrared light have attracted attention owing to their potential applications including window coating with heat-shielding property. However, photonic crystals with an optical function in practical use sometimes lose their function because of contamination. Here, a near-infrared reflection coating film with self-healing omniphobicity was designed and prepared by layer-by-layer assembly and an instant liquid phase omniphobization method. The fabricated films had a self-cleaning thermal shielding effect. The films were visually transparent and could be used to control the reflection peak of the near-infrared light (range of 700-1000 nm) by adjusting the film thickness, which prevented the increase in temperature in enclosed spaces. After omniphobization, the films had self-cleaning properties of their surface and retained their optical properties. These functions are promising for practical application on windows as heat-shielding.

Novel Deep-Eutectic-Solvent-Infused Carbon Nanofiber Networks as High Power Density Green Battery Cathodes.

Redox flow batteries (RFBs) have emerged as a promising candidate for large-scale energy storage because of the flexible design for high energy, power, and safety. In this study, FeCl3·6H2O/urea composite deep eutectic catholyte (FeU-DEC)-infused self-standing carbon nanofiber (CNF) was synthesized for green and high power density RFB through industrially available processes. FeU-DEC-infused CNF displayed an extremely high power density (874 mW/g) as well as high capacity (27.28 mAh/g) derived from high theoretical capacity of FeU-DEC (89.24 mAh/g) in addition to the advantages of the FeU-DEC characteristics (e.g., nonflammable, biodegradable, facile preparation). This is because of the large electroactive area derived from the high surface area of CNF and superlyophilicity of FeU-DEC on CNFs. Furthermore, we compared the wettability of CNF with other electrodes, as well as the chemical stability and electrode performance, based on topological wetting analysis using parameters of fiber radius, fiber interval, the equilibrium contact angle of FeU-DEC on electrodes, and surface tension of FeU-DEC, giving wetting threshold for FeU-DEC on fibrous electrodes. The wetting analysis are applied not only for FeU-DEC, but also for a wide range of other DECs and deep eutectic anolyte. This work contributes to the further development of green and high-performance RFBs.

A new 'sticking' coating method for the in situ formation of nanofiber networks on micrometer to millimeter-sized surfaces.

A simple versatile method to form a nanofiber coating in situ on micrometer to millimeter-sized surfaces is developed. A fiber-filled porous sheet is designed by electrospinning a dense polymer solution on a patterned PET/aluminum alloy collector. By sticking the small area surface onto a fiber-filled porous sheet, a nanofiber-coated small area surface is obtained, which overcomes conventional nanofiber coating difficulties.

A Fluorine-free Slippery Surface with Hot Water Repellency and Improved Stability against Boiling.

Inspired by natural living things such as lotus leaves and pitcher plants, researchers have developed many excellent antifouling coatings. In particular, hot-water-repellent surfaces have received much attention in recent years because of their wide range of applications. However, coatings with stability against boiling in hot water have not been achieved yet. Long-chain perfluorinated materials, which are often used for liquid-repellent coatings owing to their low surface energy, hinder the potential application of antifouling coatings in food containers. Herein, we design a fluorine-free slippery surface that immobilizes a biocompatible lubricant layer on a phenyl-group-modified smooth solid surface through OH-π interactions. The smooth base layer was fabricated by modification of phenyltriethoxysilane through a sol-gel method. The π-electrons of the phenyl groups interact with the carboxyl group of the oleic acid used as a lubricant, which facilitates immobilization on the base layer. Water droplets slid off the surface in the temperature range from 20 to 80 °C at very low sliding angles (<2°). Furthermore, we increased the π-electron density in the base layer to strengthen the OH-π interactions, which improved long-term boiling stability under hot water. We believe that this surface will be applied in fields in which the practical use of antifouling coatings is desirable, such as food containers, drink cans, and glassware.

In Situ Formation of Slippery-Liquid-Infused Nanofibrous Surface for a Transparent Antifouling Endoscope Lens.

Slippery-liquid-infused porous surfaces (SLIPS) are state-of-the-art materials owing to their excellent properties derived from their fluidity (e.g., dynamic omniphobicity and self-healing function). Although SLIPS have been multifunctionalized and developed for various applications, the fabrication process is not well advanced because it is time-consuming and requires multiple steps. Here, a versatile method is reported for the instant formation of slippery surfaces in situ. A lubricated fiber-filled porous sheet was designed, and a coating was formed simply by sticking a surface to the sheet. This sheet can be used as a "disposable instant coating kit" and be made available for instant and repeated coating of SLIPS. The technique is applied to a transparent antifouling endoscope lens as a proof-of-concept. This work improves the fabrication process of SLIPS and contributes to the practical use of SLIPS.

Antiadhesion Function between a Biological Surface and a Metallic Device Interface at High Temperature by Wettability Control.

During operations, medical doctors use various medical equipment that is mainly manufactured from metallic materials. Bipolar forceps are used for electrosurgery, especially neurosurgery. Bipolar forceps are utilized for cutting, inosculation, and quick hemostasis with electricity. Because bipolar tips reach a high temperature, the tissue that makes contact with the tips and nearby tissue is damaged. In addition, operations are delayed because of the need to wash or change equipment because of tissue adhering to the bipolar tips. Herein, we designed bipolar forceps with antiadhesion properties by coating them with a superhydrophobic material. We compared the effect of the coating by using bipolar forceps in different tissue samples and target areas, which reached different surface temperatures. Furthermore, the effect of the surface wettability was investigated. The temperature measurements and adhesion force measurements indicated that coating of the sample significantly limited the temperature increase and reduced the adhesion force. We demonstrated that the antiadhesion properties depended on the change in the surface tension of the hydrophobic material coating. These coatings are promising for decreasing tissue adhesion on metallic devices and decreasing collateral heat damage to the tissue.

Facile synthesis of a high electrical and ion conductivity junction-less 3D carbon sponge electrode for self-standing lithium ion battery anode.

Lithium ion batteries (LIB) are the most extensively researched and developed batteries. Currently, LIBs are used in various applications such as electric vehicles (EV), hybrid EVs (HEV), plug-in HEVs, and energy storage systems. However, their energy density is insufficient and further improvement is required. In this study, we propose the facile synthesis of a self-standing, junction-less 3D carbon sponge electrode (3DCS) for improving the energy density. A self-standing structure can improve the energy density by reducing non-active materials such as binders and current collectors, in electrodes. We use a kitchenware melamine sponge as the carbon precursor. The utilization of materials mass-produced by existing facilities is crucial for ensuring availability and low costs. Such characteristics are imperative for industrialization. These self-standing 3DCS electrodes, fabricated using available low-cost melamine sponges, demonstrate high charge-rate characteristics with a capacity retention of 81.8% at 4000 mA g-1 and cycle durability with 95.4% capacity retention after 500 cycles, without current collector, binder, and conductive additives. This high availability, low-cost material with excellent characteristics is beneficial for research institutions and companies that do not have facilities.

A Lubricant-Sandwiched Coating with Long-Term Stable Anticorrosion Performance.

Lubricant-infused surface(s) (LIS) bioinspired by the Nepenthes pitcher plant are receiving enormous attention owing to their excellent hydrophobicity as well as their self-healing ability. Thus, they have been applied as anticorrosion coatings. However, the loss of lubricant mediated by vapor or other liquids deteriorates their functions. Herein, we introduce a lubricant-inserted (sandwiched) microporous triple-layered surface (LIMITS) that prevents the sudden loss of lubricant. The sandwiched lubricant gradually self-secretes toward the surface, resulting in long-term stability even under water. The LIMITS prevented the corrosion of the Fe plate for at least 45 days, which is much superior to a conventional LIS coating. This work opens an avenue for the application of slippery coating materials that are stable under water and will also promote the development of anticorrosion coating in various industries.

Ultrasensitive Detection of Methylmercaptan Gas Using Layered Manganese Oxide Nanosheets with a Quartz Crystal Microbalance Sensor.

Methylmercaptan (MM) is a marker of periodontal disease; however, the required sensitivity for MM is parts per billion, which has been challenging to realize with a simple sensor. Here, we report the capability to detect MM at concentrations as low as 20 ppb using layered manganese oxide nanosheets with a quartz crystal microbalance sensor. The sensing capabilities of the manganese oxide nanosheets are promoted by adsorbed water present on and between the nanosheets. The strong adsorption of MM to the sensor, which is necessary for the high sensitivity, leads to significant hysteresis in the response on cycling due to irreversible adsorption. However, the sensor can be readily reset by heating to 80 °C, which leads to highly reproducible response to MM vapor at low concentrations. A key aspect of this sensor design is the high selectivity toward MM in comparison to other compounds such as ethanol, ammonia, acetaldehyde, acetic acid, toluene, and pyridine. This layered nanosheets design for high-sensitivity sensors, demonstrated here for dilute MM, holds significant promise for addressing needs to identify sulfur compounds associated for environmental protection and medical diagnostics.

Trace Material Capture by Controlled Liquid Droplets on a Superhydrophobic/Hydrophilic Surface.

A liquid droplet in contact with a superhydrophobic surface can be used to collect dissolved trace materials after evaporating the solvent. This process effect enhances detection limits, but a liquid droplet easily rolls off a superhydrophobic surface. Keeping it at a specific collecting spot area is challenging. Here the means for controlling and capturing a liquid droplet on a superhydrophobic surface is demonstrated. To induce a liquid droplet to a collecting spot, its rolling direction was controlled by two superhydrophobic fabric guides. The liquid droplet was then captured by hydrophilic polymer and hydrophilic nanoparticles at the measuring spot. After removing the solvent, the trace compounds were evaluated with a colorimetric analysis visible to the naked eye.

Liquid-Infused Smooth Surface for Improved Condensation Heat Transfer.

Control of vapor condensation properties is a promising approach to manage a crucial part of energy infrastructure conditions. Heat transfer by vapor condensation on superhydrophobic coatings has garnered attention, because dropwise condensation on superhydrophobic surfaces with rough structures leads to favorable heat-transfer performance. However, pinned condensed water droplets within the rough structure and a high thermodynamic energy barrier for nucleation of superhydrophobic surfaces limit their heat-transfer increase. Recently, slippery liquid-infused surfaces (SLIPS) have been investigated, because of their high water sliding ability and surface smoothness originating from the liquid layer. However, even on SLIPS, condensed water droplets are eventually pinned to degrade their heat-transfer properties after extended use, because the rough base layer is exposed as infused liquid is lost. Herein, we report a liquid-infused smooth surface named "SPLASH" (surface with π electron interaction liquid adsorption, smoothness, and hydrophobicity) to overcome the problems derived from the rough structures in previous approaches to obtain stable, high heat-transfer performance. The SPLASH displayed a maximum condensation heat-transfer coefficient that was 175% higher than that of an uncoated substrate. The SPLASH also showed higher heat-transfer performance and more stable dropwise condensation than superhydrophobic surfaces and SLIPS from the viewpoints of condensed water droplet mobility and the thermodynamic energy barrier for nucleation. The effects of liquid-infused surface roughness and liquid viscosity on condensation heat transfer were investigated to compare heat-transfer performance. This research will aid industrial applications using vapor condensation.

Bioinspired Hand-Operated Smart-Wetting Systems Using Smooth Liquid Coatings.

Manually controllable "hand-operated" smart systems have been developed in many fields, including smart wetting materials, electronic devices, molecular machines, and drug delivery systems. Because complex morphological or chemical control are generally required, versatile strategies for constructing the system are technologically important. Inspired by the natural phenomenon of raindrops rarely bouncing and usually spreading on a puddle, we introduce a droplet-impact-triggering smart-wetting system using "non-smart" smooth liquid coating materials. Changing the droplet impact energy by changing the volume or casting height causes the droplet to completely bounce or spread on the liquid surface, regardless of the miscibility between the two liquids, owing to the stability of air layer. As the bouncing of a droplet on a liquid interface is not usually observed during wetting, we first analyze how the droplet bounces, then prove that the wettability is triggered by the droplet's impact energy, and finally introduce some applications using this system.

Slippery Liquid-Immobilized Coating Films Using in Situ Oxidation-Reduction Reactions of Metal Ions in Polyelectrolyte Films.

We fabricated slippery liquid-immobilized coating (SLIC) films by reacting a slippery liquid (polymethylhydrosiloxane) near the surface of a polyelectrolyte film containing silver ions prepared by the layer-by-layer method. The obtained films maintained their slipperiness after chemical and physical treatments, in contrast to slippery liquid-infused porous surfaces. The high chemical and physical stabilities of the films were attributable to gelation and immobilization of the lubricant owing to an oxidation-reduction reaction with subsequent dehydration condensation of Si-OH on the outer surface of the polyelectrolyte film and the bonding of Si-H with NH2 groups within the polyelectrolyte film, respectively. Moreover, the SLIC films exhibited a high degree of slipperiness with respect to low-surface-tension liquids. To the best of our knowledge, this technique of lubricant immobilization using silver ions has not been reported previously. The films should be suitable for use in various applications where contamination must be prevented under extreme conditions, such as those requiring high physical durability and organic solvent use.

Droplet Motion Control on Dynamically Hydrophobic Patterned Surfaces as Multifunctional Liquid Manipulators.

In this letter, we introduce a novel liquid manipulation strategy to design dynamically hydrophobic and statically hydrophobic/hydrophilic patterned surfaces using an "omniphobicity"-based technique. The surfaces guide the sliding direction of a droplet in the presence of a statically hydrophilic area where the droplet does not stick on the transport path significantly enhancing the fluidic system transport efficiency. The concept of dynamically hydrophobic and statically hydrophobic/hydrophilic patterned surfaces in conjunction with omniphobic patterning techniques having surface multifunctionality, we believe, has potential not only for fluidic applications but also for future material engineering development.

Chitin Nanofibers Extracted from Crab Shells in Broadband Visible Antireflection Coatings with Controlling Layer-by-Layer Deposition and the Application for Durable Antifog Surfaces.

Reflection from various surfaces of many optical systems, such as photovoltaics and displays, is a critical issue for their performance, and antireflection coatings play a pivotal role in a wide variety of optical technologies, reducing light reflectance loss and hence maximizing light transmission. With the current movement toward optically transparent polymeric media and coatings for antireflection technology, the need for economical and environmentally friendly materials and methods without dependence on shape or size has clearly been apparent. Herein, we demonstrate novel antireflection coatings composed of chitin nanofibers (CHINFs), extracted from crab shell as a biomass material through an aqueous-based layer-by-layer self-assembly process to control the porosity. Increasing the number of air spaces inside the membrane led low refractive index, and precise control of refractive index derived from the stacking of the CHINFs achieved the highest transmittance with investigating the surface structure and the refractive index depending on the solution pH. At a wavelength of 550 nm, the transmittance of the coatings was 96.4%, which was 4.8% higher than that of a glass substrate, and their refractive index was 1.30. Further critical properties of the films were the durability and the antifogging performance derived from the mechanical stability and hydrophilicity of CHINFs, respectively. The present study may contribute to a development of systematically designed nanofibrous films which are suitable for optical applications operating at a broadband visible wavelength with durability and antifog surfaces.