Seimei Shiratori

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.

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.

Influence of carbonization temperature and press processing on the electrochemical characteristics of self-standing iron oxide/carbon composite electrospun nanofibers

Lithium ion batteries (LIBs) are popular energy storage devices used in various fields such as electronics, mobilities, and power devices. In recent years, LIBs have been used in applications that require high energy densities to improve device performance metrics such as weight saving and miniaturization, as well as for reducing the cost. In this study, we propose two solutions for meeting the high energy density demands of these applications, namely (i) the use of active materials with high energy density and (ii) reduction of non-active materials such as the conductive agent, binder, separator, and electrolyte in the battery systems. In this study, we investigate the role of carbonization temperature and press processing of iron oxide/carbon composite nanofibers in improving the electrochemical characteristics of these electrode materials. The results of the study indicate that increasing the carbonization temperature improves the energy density per unit weight and unit volume as well as the rate capabilities, whereas press processing improves the energy density per unit volume, but reduces the rate capabilities. The investigation is useful for improving the performance of iron oxide/carbon composite nanofibers as the anode for LIBs.

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.

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.