Electrothermally Triggered Broadband Optical Switch Films with Extremely Low Power Consumption

Smart films with transmittance switching capabilities based on thermal stimuli are widely used in many optoelectronic applications. Despite the development of stably switchable materials, transition temperature control and broadband stepwise transmittance switching remain challenging topics. Additionally, reduction of the energy consumption during switching is also required. Here, we introduce an electrothermally driven film with switchable transmittance produced by stacking paraffin-immobilized polydimethylsiloxane gel on a transparent heater based on an aligned Cu/Ni network. The film shows stepwise transmittance switching capability with extremely low power consumption because of the controlled melting point of paraffin and the high-efficiency transparent heater

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

Asymmetric Superhydrophobic/Superhydrophilic Cotton Fabrics Designed by Spraying Polymer and Nanoparticles

Inspired by the special wettability of certain natural life forms, such as the high water repellency of lotus leaves, many researchers have attempted to impart superhydrophobic properties to fabrics in academic and industrial contexts. Recently, a new switching system of wettability has inspired a strong demand for advanced coatings, even though their fabrication remains complex and costly. Here, cotton fabrics with asymmetric wettability (one face with natural superhydrophilicity and one face with superhydrophobicity) were fabricated by one-step spraying of a mixture of biocompatible commercial materials, hydrophobic SiO₂ nanoparticles and ethyl-α-cyanoacrylate superglue. Our approach involves controlling the permeation of the fabric coatings by changing the distance between the fabric and the sprayer, to make one side superhydrophobic and the other side naturally superhydrophilic. As a result, the superhydrophobic side, with its high mechanical durability, exhibited a water contact angle of 154° and sliding angle of 16°, which meets the requirement for self-cleaning ability of surfaces. The opposite side exhibited high water absorption ability owing to the natural superhydrophilic property of the fabric. In addition, the designed cotton fabrics had blood absorption and clotting abilities on the superhydrophilic side, while the superhydrophobic side prevented water and blood permeation without losing the natural breathability of the cotton. These functions may be useful in the design of multifunctional fabrics for medical applications

Optically Transparent Superhydrophobic Surfaces with Enhanced Mechanical Abrasion Resistance Enabled by Mesh Structure

Inspired by naturally occurring superhydrophobic surfaces such as “lotus leaves”, a number of approaches have been attempted to create specific surfaces having nano/microscale rough structures and a low surface free energy. Most importantly, much attention has been paid in recent years to the improvement of the durability of highly transparent superhydrophobic surfaces. In this report, superhydrophobic surfaces are fabricated using three steps. First, chemical and morphological changes are generated in the polyester mesh by alkaline treatment of NaOH. Second, alkaline treatment causes hydrophobic molecules of 1<i>H</i>,1<i>H</i>,2<i>H</i>,2<i>H</i>-perfluorodecyltrichlorosilane to react with the hydroxyl groups on the fiber surfaces forming covalent bonds by using the chemical vapor deposition method. Third, hydrophobicity is enhanced by treating the mesh with SiO₂ nanoparticles modified with 1<i>H</i>,1<i>H</i>,2<i>H</i>,2<i>H</i>-perfluorooctyltriethoxysilane using a spray method. The transmittance of the fabricated superhydrophobic mesh is approximately 80% in the spectral range of 400–1000 nm. The water contact angle and the water sliding angle remain greater than 150° and lower than 25°, respectively, and the transmittance remains approximately 79% after 100 cycles of abrasion under approximately 10 kPa of pressure. The mesh surface exhibits a good resistance to acidic and basic solutions over a wide range of pH values (pH 2–14), and the surface can also be used as an oil/water separation material because of its mesh structure

Optically Transparent Superhydrophobic Surfaces with Enhanced Mechanical Abrasion Resistance Enabled by Mesh Structure

Inspired by naturally occurring superhydrophobic surfaces such as “lotus leaves”, a number of approaches have been attempted to create specific surfaces having nano/microscale rough structures and a low surface free energy. Most importantly, much attention has been paid in recent years to the improvement of the durability of highly transparent superhydrophobic surfaces. In this report, superhydrophobic surfaces are fabricated using three steps. First, chemical and morphological changes are generated in the polyester mesh by alkaline treatment of NaOH. Second, alkaline treatment causes hydrophobic molecules of 1<i>H</i>,1<i>H</i>,2<i>H</i>,2<i>H</i>-perfluorodecyltrichlorosilane to react with the hydroxyl groups on the fiber surfaces forming covalent bonds by using the chemical vapor deposition method. Third, hydrophobicity is enhanced by treating the mesh with SiO₂ nanoparticles modified with 1<i>H</i>,1<i>H</i>,2<i>H</i>,2<i>H</i>-perfluorooctyltriethoxysilane using a spray method. The transmittance of the fabricated superhydrophobic mesh is approximately 80% in the spectral range of 400–1000 nm. The water contact angle and the water sliding angle remain greater than 150° and lower than 25°, respectively, and the transmittance remains approximately 79% after 100 cycles of abrasion under approximately 10 kPa of pressure. The mesh surface exhibits a good resistance to acidic and basic solutions over a wide range of pH values (pH 2–14), and the surface can also be used as an oil/water separation material because of its mesh structure

One-Step Dipping Fabrication of Fe₃O₄/PVDF-HFP Composite 3D Porous Sponge for Magnetically Controllable Oil–Water Separation

Industrial oil spills in various bodies of water is a worldwide environmental problem that requires effective oil absorbents with remote controllability, which would be a clear improvement upon currently used technologies. One approach for adding remote controllability is embedding magnetic particles into the oil absorbent materials; however, there are currently few reports of magnetic oil absorbents. Most of these are prepared through multistep processes or using hazardous materials, which inhibits their practical use. In this study, we introduce a single-step dipping method to simultaneously provide both magnetic and hydrophobic/oleophilic functions to melamine foam by combining hydrophobic flexible copolymer poly­(vinylidene fluoride-<i>co</i>-hexafluoropropylene) (PVDF-HFP) and magnetic Fe₃O₄ nanoparticles synthesized by a method suitable for mass production. The as-fabricated coating performs effectively for oil collection of oil spilled on water, and the movement of the foam on the water’s surface can be effectively controlled under magnetic field without touching it directly. Also, the coating is capable of regenerating its oil-absorbing property by being wrung out after the initial absorption owing to its flexibility and separation of oil in a water-in-oil emulsion. Such a simple method for the creation of multifunction material could potentially be helpful for the development of commercial remediation materials