A thermoresponsive smart window that can switch its transmittance to control heating from sunlight is attracting great attention. Such windows made from a hydrogel of a thermoresponsive polymer such as poly­(N-isopropylacrylamide) (PNIPAm) or hydroxypropyl cellulose (HPC) have been successful and can switch their transmittance at room temperature. However, such hydrogels occasionally freeze in cold places, degrading their transmittance. Thus, a thermoresponsive hydrogel that can be used in various geographical regions is desired. Here, we produced a thermoresponsive smart window with freezing resistance made from HPC and glycerol. We could adjust its switching temperature by simply changing the amount of added glycerol, letting us easily change it to room temperature for practical use. These smart windows show high cyclic performance, freezing resistance, and heat shielding, demonstrating great potential.

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.

Endoscopic surgery is a minimally invasive approach that is widely used in various clinical departments, including digestive surgery, thoracic surgery, and urology, because it can minimize the burden on patients. To perform more elaborate procedures, highly functional coatings that enhance the operation efficiency of the related equipment are required; for example, coatings to improve the visibility through endoscope lenses are needed. In this study, we designed multifunctional surfaces that displayed antithrombogenicity, antireflection, and antifogging by controlling nano-ordered hierarchical structures fabricated via layer-by-layer self-assembly. The coatings were composed of polyelectrolyte multilayers prepared from blends of poly(vinyl alcohol) (PVA) and poly(acrylic acid) (PAA) that were deposited in alternating layers with blends of poly(allylamine hydrochloride) (PAH), PVA, and PAA. Although mixing cationic PAH and anionic PAA solutions generally causes polyelectrolyte−polyelectrolyte complexes (PECs) to form through electrostatic interactions, we found that PAH and PAA hardly formed PECs when PVA was present in the solution containing PAA. Consequently, PAA behaved differently in cationic and anionic solutions, resulting in the formation of coatings with hierarchical texture. The structures possessed antireflective properties with a graded refractive index and >95% transmittance. The coatings also displayed resistance to protein adsorption derived from free hydroxyl groups and antifogging performance caused by hydrophilicity combined with the strong hydrogen bonding ability of PVA. The results of this study would be valuable for the development of innovative biomedical devices through a simple and environmentally friendly approach.