Universal Low-Temperature Process for Preparation of Multifunctional High-Performance Antireflective Mesoporous Silica Coatings on Transparent Polymeric Substrates

Flexible Antireflection Coatings with Enhanced Durability and Antifogging Properties

Antireflection coatings (ARCs) enhance optical clarity and improve light transmission by reducing glare and reflections. The application of conventional ARCs in flexible devices, however, is impeded by their lack of durability, particularly under bending deformation. We develop ARCs that withstand delamination and fracture, remaining intact even after 1000 bending cycles with a 5 cm bending radius. We fabricate integrated ARCs (iARCs) on a poly(methyl methacrylate) (PMMA) substrate by inducing free polymers to infiltrate the interstices of a disordered assembly of hollow silica nanochains and nanospheres. The polydispersity of PMMA creates a refractive index gradient, yielding a broadband antireflection capability. The nanochain-based iARCs are superior to the nanosphere-based coatings in both antireflection properties and mechanical durability, owing to the lower packing density and mechanical interlocking of the nanochains, respectively. Additionally, these nanochain iARCs display antifogging properties stemming from their superhydrophilicity. While our demonstrations are based on PMMA as a model substrate, this methodology is potentially extendable to other polymers, enhancing the iARC's applicability across various practical applications, including flexible and wearable devices.

Recent advances in prevailing antifogging surfaces: structures, materials, durability, and beyond

In past decades, antifogging surfaces have drawn more and more attention owing to their promising and wide applications such as in aerospace, traffic transportation, optical devices, the food industry, and medical and other fields. Therefore, the potential hazards caused by fogging need to be solved urgently. At present, the up-and-coming antifogging surfaces have been developing swiftly, and can effectively achieve antifogging effects primarily by preventing fog formation and rapid defogging. This review analyzes and summarizes current progress in antifogging surfaces. Firstly, some bionic and typical antifogging structures are described in detail. Then, the antifogging materials explored thus far, mainly focusing on substrates and coatings, are extensively introduced. After that, the solutions for improving the durability of antifogging surfaces are explicitly classified in four aspects. Finally, the remaining big challenges and future development trends of the ascendant antifogging surfaces are also presented.

Enhanced Mechanical and Hydrophobic Antireflective Nanocoatings Fabricated on Polycarbonate Substrates by Combined Treatment of Water and HMDS Vapor

Polycarbonate (PC) with high transmittance, stable mechanical performance and environmental resistance is crucial for practical applications. In this work, we report a method for the preparation of a robust antireflective (AR) coating by a simple dip-coating process of a mixed ethanol suspension consisting of tetraethoxysilane (TEOS) base-catalyzed silica nanoparticles (SNs) and acid-catalyzed silica sol (ACSS). ACSS greatly improved the adhesion and durability of the coating, and the AR coating exhibited high transmittance and mechanical stability. Water and hexamethyldisilazane (HMDS) vapor treatment were further employed to improve the hydrophobicity of the AR coating. The as-prepared coating exhibited excellent antireflective properties, with an average transmittance of 96.06% in the wavelength range of 400 to 1000 nm, which is 7.55% higher than the bare PC substrate. After sand and water droplet impact tests, the AR coating still maintained enhanced transmittance and hydrophobicity. Our method shows a potential application for the preparation of hydrophobic AR coatings on a PC substrate.

Novel Antireflection Coatings Obtained by Low-Temperature Annealing in the Presence of Tetrabutylammonium Bromide and Gold Nanoparticles

In this work, nanoporous antireflective coatings on silicate glass were obtained from silicon dioxide sol compositions by the sol-gel method in the presence of quaternary ammonium salt (tetrabutylammonium bromide) at different annealing temperatures (200-250 °C). Varying the salt concentration from 3 to 5 wt.%, we achieved the transmittance of the coatings of about 97% at 250 °C in comparison with 91% for clean glass in the wavelength range from 400 to 1100 nm. The addition of gold nanoparticles to the composition containing 5 wt.% tetrabutylammonium bromide allowed us to decrease the annealing temperature to 200 °C, preserving the transmittance at the level of 96.5%. For this case, the optimal concentration of gold nanoparticles is determined (2.6 × 10^-9 mol/mL). According to the SEM analysis, the obtained antireflective coatings contain pores with a minimum area size up to 4 nm².

Transparent polyimide films with ultra-low coefficient of thermal expansion

According to the application requirements of colorless transparent polyimide (CPI) film for low coefficient of thermal expansion (CTE) in the field of OLED display, the new aromatic dianhydride monomers with amide bond structure were synthesized, namely s-ABDA, i-ABDA, EADA. Furthermore, a series of CPI films were prepared by two-step method from the reaction of as-synthesized dianhydrides with 2.2′-bis (trifluoromethyl) −4.4′-diaminobiphenyl (TFMB) or trans-1.4′-cyclohexanediamine ( t-CHDA). Based on the analysis of performance results, the incorporation of amide group and biphenyl, benzene or ether bond into dianhydride monomer helped this new type of transparent polyimide film with excellent optical properties (T550 nm> 88%), great heat stability (CTE < 4.4 ppm/K; Tg > 314°C; Td5% > 478°C) and good mechanical strength (σ > 208 MPa). The film s-ABDA/TFMB showed ultra-low CTE value at 4.4 ppm/K, aligning with the maximum birefringence, indicating that the role of hydrogen bonding was of great benefit to the regulation of thermal expansion.

Embedding constructed refractive index graded antireflective coating with high abrasion resistance and environmental stability for polycarbonate glass

Polycarbonate (PC) is a durable and transparent optical plastic material commonly used as shatter-resistant alternative to traditional optical glass. Broadband antireflective (AR) coatings with excellent mechanical strength and environmental stability are essential for PC to achieve high light transmission and visual quality. In this work, chloroform vapor treatment was employed to partially embed the silica coating into the PC substrate for adhesion enhancement, which also divided the silica coating layer into bottom and middle layers with different refractive indices. The contact between the silica nanoparticles and the substrate was transformed from "point-contact" to "area-contact", which enhanced the adhesion between coating and PC substrate. After the deposition of a top layer coating consisted of silica nanoparticles with smaller diameter, a triple-layer refractive index graded AR structure was constructed. Hexamethyldisilazane vapor surface modification was performed to decrease the surface free energy of top coating layer. The triple-layer coating coated PC exhibits superior antireflection property with an average reflectance of only 0.43% over a wide wavelength range of 400-1000 nm. After 100 times of friction or 5 months of exposure to a contaminated environment, the reflectance of coated PC shows barely noticeable difference, indicating its excellent mechanical strength and environmental stability.

Synthesis and characterization of amide-bridged colorless polyimide films with low CTE and high optical performance for flexible OLED displays

Starting from three novel amide-incorporating dianhydride monomers, we synthesized a series of amide-bridged cPI films that have ultra-low CTE and high Tg due to the formation of hydrogen bonds as well as great optical performance.

Nanostructured Hybrid-Material Transparent Surface with Antireflection Properties and a Facile Fabrication Process

Highly transparent optical surfaces with antireflection (AR) properties have the potential to increase the performance of a wide range of applications, such as windows for photovoltaic cells, photodetectors, and display screens among others. Biomimetic structures inspired by the moth-eye have attracted much attention as they can offer superior AR properties, which can generate broadband, omnidirectional optical transmission, and water-repellent self-cleaning behavior. However, many biomimetic surfaces suffer from time-consuming and complex processing, for example, electron beam and nanoimprint lithography, and/or sub-optimal mechanical reliability. In this paper, we introduce a hybrid material approach-nanostructured polyimide on a substrate-for demonstrating a surface with significant AR and hydrophobic properties together with low scattering (haze) and high mechanical resistance. As an example of applications, we demonstrate an indium tin oxide transparent conductive substrate with a large AR effect and optical transmission associated to the nanostructured polyimide coating. The proposed design and method based on conventional spin-coating and lithography-free metal dewetting have the potential to be a low-cost processing path of nanostructured AR transparent substrates.

Low-Temperature Preparation of Mechanically Robust and Contamination-Resistant Antireflective Coatings for Flexible Polymeric Glasses via Embedding of Silica Nanoparticles and HMDS Modification

Mechanical and contamination-resistant properties are the most crucial and challenging issues that impede the practical applications of sol-gel antireflective (AR) coating. In this paper, we report a low-temperature vapor surface treatment strategy for the partial embedding and surface functionalization of silica nanoparticles (SNPs) on flexible polymeric glass substrates. SNPs, which were synthesized via the Stöber method, were partially embedded into the polymeric glass substrates by vapor-phase surface treatment using volatile chloroform. Further vapor-phase surface treatments by water and hexamethyldisilazane (HMDS) were applied successively to achieve high trimethylsilyl coverage of the SNPs. The HMDS modification could convert the polar surface of SNPs to a nonpolar surface for contamination resistance, while ammonia, as a byproduct generated, could help to cross-link the SNPs via self-condensation of silanol groups, thus hardening the coating. The SNP-CWH coated polymethylmethacrylate (PMMA) substrate shows an average transmittance of 98.62% in the wavelength region of 400-800 nm, which is 6.32% higher than that of the uncoated bare PMMA. The AR performance of SNP-CWH coated PMMA shows almost no degradation after 100 times of rubbing or bending, indicating the greatly enhanced abrasion resistance and flexibility. Furthermore, the SNP-CWH coating exhibits superior contamination-resistant property, where the transmittance curve of the coated substrate displays a barely noticeable change after exposure to a "dirty" environment with water and organic contaminants for 6 months. This work paves a new way for developing mechanically robust and contamination-resistant AR coating for polymeric substrates.

Bio-inspired antifogging PDMS coupled micro-pillared superhydrophobic arrays and SiO2 coatings

In this work, inspired by some typical creatures from nature with superhydrophobic surfaces, a bio-inspired antifogging PDMS is designed and fabricated successfully using UV lithography and a template method. First, we fabricated an SU-8 layer with a bio-inspired micro-pillared array (MPA) using traditional UV lithography. Then, it was used as a template to fabricate a PDMS film (PF). After that, it was chemically modified with SiO2 coatings. It was found that the PF coupled with sprayed SiO2 coatings and a MPA have a higher water contact angle (CA) of 158° and a lower contact angle hysteresis (CAH) of less than 2°. Water drops can be separated from this bio-inspired PDMS surface within 86.8 ms. More importantly, this film's antifogging property is superior, with a recovery time of less than 13 s, which is significantly superior to that of the flat PF and the PF with the MPA. Afterwards, FTIR was applied to analyse the surface chemistry features and suggested that the bio-inspired PF has extremely low surface tension. So, it can be confirmed that an excellent superhydrophobic antifogging property has been achieved on the surface of the PF. Meanwhile, the microscopic and macroscopic dynamic movement behaviour of the fog drops was further observed. Then, the underlying antifogging mechanism was also revealed. These properties mainly benefit from the coupling effect of intermolecular attraction of droplets, chemical compositions (nanometre roughness SiO2) and the physical structures (MPA). The investigations offer a promising way to handily design and fabricate multiscale hierarchical structures on polymers and other materials. More importantly, these findings suggest great potential value for specific antifogging applications in display devices, transport, agricultural greenhouses, food packaging and solar products, especially in continuous harsh fogging conditions.

Bio-inspired self-assembly of waxberry-like core-shell SiO2@TiO2 nanoparticles towards antiglare coatings

Waxberry-like core-shell SiO2@TiO2 nanoparticles were prepared by liquid-phase deposition (LPD) method. The dip-coating self-assembly of waxberry-like core-shell SiO2@TiO2 nanoparticles has been used to fabricate coatings with excellent antiglare properties in the large angle and wide wavelength range. The field emission scanning electron microscopy (SEM) and transmission electron microscopy (TEM) measurements showed that the surface of SiO2 nanoparticles were coated by titania as a shell with controllable and uniform thickness. The ultraviolet visible near-infrared spectrophotometer (UV-Vis-NIR) results indicate that the maximum transmittance of the antiglare coating is up to 95.80% in the visible band, whereas that of the pure glass substrate is only 92.10%. The scattering and haze of the films have been measured to show that such specifically structured coatings exhibited good antiglare properties in the large angle and wide wavelength range.