Vapor Deposition of Transparent Antifogging Polymeric Nanocoatings

Environmentally Friendly and All-Dry Hydrophobic Patterning of Graphene Oxide for Fog Harvesting

This study examines the fog-harvesting ability of graphene oxide surfaces patterned by hydrophobic domains. The samples were prepared from graphene deposited using low pressure chemical vapor deposition, which was later plasma oxidized to obtain hydrophilic graphene oxide (GO) surfaces. Hydrophobic domains on GO surfaces were formed by initiated CVD (iCVD) of a low-surface-energy poly(perfluorodecyl alkylate) (PPFDA) polymer. Hence, patterned surfaces with hydrophobic/hydrophilic contrast were produced with ease in an all-dry manner. The structures of the as-deposited graphene and PPFDA films were characterized using Raman and Fourier transform infrared spectrophotometer analyses, respectively. The fog harvesting performance of the samples was measured using the fog generated by a nebulizer, in which the average diameter of the fog droplets is comparable to meteorological fog. According to the fog harvesting experiment results, 100 cm2 of the as-patterned surface can collect fog up to 2.5 L in 10 h in a foggy environment. Hence, hydrophilic/hydrophobic patterned surfaces in this study can be considered as promising fog harvesting materials. Both CVD techniques used in the production of hydrophilic/hydrophobic patterned surfaces can be easily applied to the production of large-scale materials.

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.

Hydrolysis of Poly(fluoroacrylate) Thin Films Synthesized from the Vapor Phase

The post-synthesis surface reaction of vapor-deposited polymer thin films is a promising technique in engineering heterogeneous surface chemistry. Because the existing research has neglected marginally reactive precursor films in preference of their highly reactive counterparts, our knowledge of kinetics and loss of film integrity during the reaction are limited. To address these limitations, we characterize hydrolysis of two fluoroacrylates, poly(1H,1H,2H,2H-perfluorooctyl acrylate) (pPFOA) and poly(2,2,3,4,4,4-hexafluorobutyl acrylate) (pHFBA), with sodium hydroxide using X-ray photoelectron spectroscopy. Without crosslinking with di(ethylene glycol)divinyl ether (DEGDVE) and grafting with trichlorovinyl silane, the films degrade rapidly during hydrolysis. An SN2 mechanism describes hydrolysis well, with rate constants of 0.0029 ± 0.0004 and 0.011 ± 0.001 L mol-1s-1 at 30 °C for p(PFOA-co-DEGDVE) and p(HFBA-co-DEGDVE), respectively. Our detailed study of hydrolysis kinetics of marginally reactive fluoroacrylates demonstrates the full capability and limitations of the post-synthesis reaction. Importantly, copolymers are characterized using a density correction new to polymer chemical vapor deposition.

Transparent Composite Films Showing Durable Antifogging and Repeatable Self-Healing Properties Based on an Integral Blend Method

Antifogging coatings for infrastructures and transparent objects have attracted much attention lately from the perspective of safety and visibility. We have developed a one-pot process to fabricate transparent composite films showing long-lasting antifogging and fast repeatable self-healing properties based on an integral blend (IB) method. This method does not require any specific pretreatments of inorganic fillers/particles. Thus, the precursor solutions could be prepared in a single step by simply mixing raw materials, e.g., poly(vinylpyrrolidone) (PVP) having different molecular weights (MWs: 55, 360, and 1300 k), nano-clay particles (NCPs), and amino-terminated organosilane (AOS). In this study, to control the degree of cross-linking between the PVP matrices and NCPs, addition of AOS as a cross-linker to the PVP matrices (weight percentage of AOS to the PVP matrices, α = 0.01-300%) was carefully controlled. Transparency and self-healing abilities/kinetics of the resulting samples were found to be strongly influenced by both the MWs of PVP and α values. Samples spin-coated with the lowest M_W of PVP (55 k) and α values of 0.01-1% gave highly transparent and durable antifogging performance. For example, no fogging was observed for 7 days under >80% relative humidity, and scratches about 30 μm in width could be completely self-healed within a few hours. However, samples with α > 10% gave opaque/grayish films that did not show any self-healing abilities because of an increase in cross-linking of the matrices. The optimized precursor solution was also deposited directly onto the glass slides covered with a transparent porous silica nano-framework (SNF) by a spray-coating method. Due to the formation of the hard and superhydrophilic/hygroscopic SNF with a large surface area, durability of antifogging and self-healing properties of the composite films were moderately improved, compared to those on the flat glass slides.

Robust and Transparent Antifogging Polysilsesquioxane Film Containing a Hydroxy Group

Poly(glycidyloxypropyl)silsesquioxane (PGPS) was successfully synthesized by hydrolysis and polycondensation using the nitrogen flow method. A poly(3-(2,3-dihydroxypropoxypropyl)silsesquioxane) (PSQ-OH) film was prepared via two routes. In route A, PSQ-OH was prepared by the hydrolysis of the epoxy group of PGPS in an aqueous hydrochloric acid (HCl)/tetrahydrofuran solution, affording a diol group; then, PSQ-OH was coated on a glass substrate and heated. The antifogging performance of the PSQ-OH film was evaluated in terms of water uptake (WU) and scratch resistance. The obtained PSQ-OH film exhibited a low WU of 5% and a scratch resistance of 1.6. In route B, PGPS was coated on a glass substrate and immersed in a 0.5 mol/L aqueous sulfuric acid solution for 1-15 h at room temperature, producing a diol group. The solid-state ¹³C nuclear magnetic resonance spectrum indicated that the epoxy group was completely hydrolyzed after immersion for 15 h. The WU of the PSQ-OH film prepared via route B increased from 5 to 19% with the increase in the immersion time and was higher than that of the PSQ-OH film prepared via route A. The PSQ-OH film on a glass substrate retained transparency under water vapor exposure at 60 °C. The PSQ-OH film prepared via route B exhibited a high scratch resistance of 2.7-3.6, similar to that of a poly(3-(2-aminoethylaminopropyl)silsesquioxane) film. The scratch resistance of the PSQ-OH film was 5-7 times higher than that of the poly(vinyl alcohol) film. The PSQ-OH film was uniform with no pinholes and cracks. The PSQ-OH film was transparent and colorless and exhibited a high transmittance of >90% in the wavelength range of 400-800 nm. Overall, the prepared PSQ-OH film exhibits good antifogging, transparency, and mechanical properties.