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.
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.
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). 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.
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 NH 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.
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