[
    {
        "id": 1,
        "chunk": "# A robust and transparent hydrogel coating for sustainable antifogging with excellent self-cleaning and self-healing ability  \n\nXuanfei $\\mathtt{X u}^{\\mathrm{a}}$ , Tianxue Zhu a,b, Weiwei Zheng a, Caiyun Xian a, Jianying Huang a, Zhong Chen c, Weilong Cai a,d, Weiying Zhang a,d,\\*, Yuekun Lai a,d,\\*  \n\nCollege of Chemical Engineering, Fuzhou University, Fuzhou 350116, PR China   \nb China National Textile and Apparel Council Key Laboratory of Flexible Devices for Intelligent Textile and Apparel, Soochow University, Suzhou 215123, PR China   \nc School of Materials Science and Engineering, Nanyang Technological University, 50 Nanyang Avenue, Singapore   \nd Qingyuan Innovation Laboratory, Quanzhou 362801, PR China",
        "category": " Abstract"
    },
    {
        "id": 2,
        "chunk": "# A R T I C L E  I N F O",
        "category": " Abstract"
    },
    {
        "id": 3,
        "chunk": "# A B S T R A C T  \n\nKeywords:   \nSelf-healing   \nTransparency   \nAntifogging   \nAntifouling   \nChemical durability  \n\nFilms with antifogging properties can be used in a wide range of fields, from manufacturing to agriculture, such as screens, camera lenses, and greenhouse films. In this study, a scraping technique was utilized to coat anti­ fogging films on polyethylene substrate by using a solution containing polyvinyl alcohol, sodium alginate, and glycerin with suspended titanium dioxide nanoparticles. The resulting hydrophilic coating has outstanding antifogging, self-healing, and anti-fouling qualities due to the polymer’s great hydration capacity. The coating also held up well during prolonged heat and ultraviolet exposure ( $40^{\\circ}\\mathrm{C}$ for 17 days and $_{192\\mathrm{h}}$ of $1.27\\mathrm{mW/cm^{2}}$ UV radiation). Furthermore, when exposed to $30~\\mathrm{g}$ sands impact from a height of 10 to $40\\ \\mathrm{cm}$ , 18 days outdoors and 1 h soaking in polar and non-polar solvents (absolute ethanol, isopropanol, n-hexane and n-hexadecane), the hydrophilicity and antifogging performance were well sustained. Different flexible/rigid substrates, such as PET, PC, PVC, and others, can be successfully coated with antifogging film by using such simple construction approach.",
        "category": " Abstract"
    },
    {
        "id": 4,
        "chunk": "# 1. Introduction  \n\nFogging in films have posed a significant obstacle to greenhouse horticulture, agricultural progress, and human life [1–2]. The formation of fog on greenhouse films may reduce the transmission of light, affecting plant photosynthesis. Furthermore, rot and breed bacteria readily thrive in the absence of appropriate light, resulting in a drastic reduction in agricultural productivity [3]. As a result, technologies or materials that can effectively prevent or reduce fogging on the agricul­ tural film surface are critical for realizing long-term sustainability and efficiency. When the temperature and humidity drop, a substantial amount of vapor in the air condenses and adheres to the surface of the substrate, forming fog. The substrate changes from transparent to opa­ que due to diffuse reflection and refraction induced by the condensed droplets [4–6].  \n\nSeveral approaches, including substrate surface heating to lessen the temperature difference, have been used to eliminate the effect of un­ desired fogging [7]. However, this technology has a disadvantage of consuming a lot of energy, which has limited its use on a big scale. There is an immediate need for a more efficient and environmentally friendly strategy. The alteration of material surface wettability has received a lot of attention [8–16]. For example, the superhydrophobic surface’s strong water-resistant properties have made it a promising contender for antifogging applications [17–25]. Jiang et al. used soft lithography to create superhydrophobic artificial compound eyes that can be used to build new antifogging coatings, inspired by mosquito compound eyes. The droplet might potentially remove polluting particles away from the surface, according to the coating’s self-cleaning characteristic. However, the superhydrophobic coating was typically inadequate in terms of robustness and process complexity, and it was also nontransparent [26].  \n\nTo solve these flaws, researchers focused their efforts on developing a super-hydrophilic film that spreads condensed droplets quickly, generating an aqueous layer with uniform thickness that allows light to pass through the substrate without scattering [27–35]. Manufacturing procedures like as dipping, knife coating, and spin coating, are frequently employed. For example, Kim et al. proposed a silica com­ posite Fe(III)-tannic acid nanocoating which underwent 5 cycles of acid and alkali, sodium percarbonate deposition for $150~\\mathrm{min}$ , and hot and cold treatment for $120\\ \\mathrm{min}$ each without structural damage, demon­ strating the durability of the coating [19]. Sun et al. developed an antifogging UV-curable coating based on raspberry-like particles and illustrated the incorporation of raspberry-like particles to significantly improve the hardness of the coating by pencil hardness test and scratch method experiments [36]. Liang et al. prepared self-healing and antifouling films with high transparency by a one pot method that can mend, severe scratches inflicted in harsh conditions. However, the modification of silicon nanoparticles was too complicated, and the coating’s mechanical qualities were insufficient to meet actual manufacturing requirements [37]. Yang et al. used the sol–gel process to make a series of $\\mathrm{Fe}^{3+}$ -doped $\\mathrm{TiO}_{2}$ films, which were then dip coated on the target substrate. The resulting sample had outstanding antifogging capabilities as well as long-lasting superhydrophilicity. However, the coatings lacked rapid self-healing ability, which make them unsuitable for long-term use [38]. Despite significant progress, difficulties like as complex production process, long-term durability against physical and chemical damage, universality for different substrates, remain unsolved.  \n\n![](images/047d2f3fd638431343ed1a08dc049454475d6fb1f537600fc156927811e87cfd.jpg)  \nScheme 1. Schematic illustration for manufacturing the antifogging PE film.  \n\n![](images/204a57385cfc8f6386d9d10d8a6fcf4056ac37eaab0c3e7ce74c52bd1dbecc83.jpg)  \nFig. 1. a) SEM photograph of the coated PE, the inset is the cross-sectional SEM image and the underwater oil contact angle of the coating. b) Corresponding mapping images of C, Na, O, and Ti elements. c) EDS spectrum and elements proportion of the PSTG coating. d) FTIR spectra of SA, PVA, $\\mathrm{TiO}_{2},$ and the as-prepared PSTG film.  \n\nHere, we present a simple approach to construct a high-transparency antifogging coating with polyvinyl alcohol (PVA), sodium alginate (SA), titanium dioxide $\\left(\\mathrm{TiO}_{2}\\right)$ , and glycerin (PSTG coating). The PSTG film exhibits a number of unique performances, including effective contam­ ination removal via self-cleaning, quick scratch healing, universality across a variety of surfaces, and outstanding antifogging capabilities. In addition, this film maintains its antifogging properties through a variety of harsh situations including prolonged lasting heat and ultraviolet treatment ( $40^{\\circ}\\mathrm{C}$ for 17 days and $_{192\\mathrm{h}}$ of $1.27\\mathrm{mW/cm^{2}}$ UV radiation), impact by $_{30\\mathrm{~g~}}$ of sands from a height of 10 to $40\\ \\mathrm{cm}$ , exposure to outdoor environments for 18 days, and $^{\\textrm{1h}}$ of soaking in polar and nonpolar solvents. The coating’s exceptional qualities have led to specula­ tion that it may be utilized in greenhouse films to prevent fog from affecting photosynthesis, as well as optically clear equipment such as windshields, periscopes, and display devices.  \n\n![](images/0f2e71f161f85d13cdeddad59bc2460b76ef075e0f89cf337998c2993bf00723.jpg)  \nFig. 2. a) Optical image of $20~\\upmu\\mathrm{L}$ methyl blue solution $(10\\mathrm{ppm})$ before and after the PSTG coating and PSG coating were exposed to $365\\mathrm{nm}$ ultraviolet light for 20 min. b) Antifogging performance of PSTG coating (top) and the water contact angles of coated PE in air (bottom). c) UV–Vis transmission spectra of the bare PE and the coated PE. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)",
        "category": " Introduction"
    },
    {
        "id": 5,
        "chunk": "# 2. Experimental section",
        "category": " Materials and methods"
    },
    {
        "id": 6,
        "chunk": "# 2.1. Materials and reagents  \n\nPVA and $\\mathrm{TiO}_{2}$ (anatase, hydrophilic $99.8\\%$ , $30\\ \\mathrm{nm}.$ ) were obtained from Aladdin. Hydrophilic anatase $\\mathrm{TiO}_{2}$ , anatase, particles, $99.8\\%$ in purity, with different sizes $20\\ \\mathrm{nm}$ , $40\\ \\mathrm{nm}$ , $60~\\mathrm{{nm}}$ , $100~\\mathrm{{nm}}.$ were pur­ chased from Macklin. SA, n-hexane, hexadecane, absolute ethanol, iso­ propanol and glycerin were purchased from Sinopharm Chemical Reagent Co., Ltd. All the materials and reagents were used without further purification. Humidifier and polyethylene film were purchased from local supermarkets.",
        "category": " Materials and methods"
    },
    {
        "id": 7,
        "chunk": "# 2.2. Methods  \n\nOrthogonal experimental design $\\mathrm{L}_{25}(5^{3})$ was selected to achieve the optimum antifogging effect and production capacity by investigating the mass concentration of raw materials. Three factors were chosen in the experiment to inspect the mass concentration of PVA (factor A), SA (factor B), and $\\mathrm{TiO}_{2}$ (factor C) (Table S1) [39]. The antifogging grade and light transmission were taken as the criteria to calculate the comprehensive score. Among them, the light transmittance is based on the blank film (average value of $400{\\mathrm{-}}720\\ \\mathrm{nm})$ ), and the light trans­ mittance of each group of samples is $0.5\\%$ higher than the blank, plus 1 point, and $0.5\\%$ lower than the blank, 1 point is deducted. The antifogging level is based on level 2, and each higher level will add 2 points, and the lower level will deduct 2 points. The experimental results of the 25 groups are listed in Table S2.  \n\nBased on these experimental results, the mass concentrations of PVA, SA and $\\mathrm{TiO}_{2}$ were chosen to be $2.78\\%$ , $0.83\\%$ and $0.025\\%$ , respectively, owing to their outstanding antifogging capacity and higher light transmittance.",
        "category": " Materials and methods"
    },
    {
        "id": 8,
        "chunk": "# 2.3. Preparation of the PSTG coating  \n\n$2.78\\mathrm{wt\\%}$ PVA, $0.83\\mathrm{wt\\%}$ SA were dissolved in $35\\mathrm{mL}$ distilled water/ glycerol solution (volume ratio of 6: 1) at $95~^{\\circ}\\mathrm{C}$ for $^{2\\mathrm{~h~}}$ to obtain a ho­ mogeneous and transparent solution, and $0.025\\mathrm{wt}\\%\\mathrm{TiO}_{2}$ particles were suspended in the solution. Here glycerol was used for enhancing the low temperature resistance of the coating, PVA and SA were used for increasing the low surface energy of the coating, $\\mathrm{TiO}_{2}$ was used for improving the aging resistance of the coating. PE membranes were treated with oxygen plasma (Yamato PM100, Japan) for $20~\\mathsf{s}$ to endow the surface with superhydrophilic ability. Subsequently, an appropriate amount of the obtained solution was scraped onto the PE substrate. Eventually, the coated PE was dried at $60~^{\\circ}\\mathrm{C}$ for $^{2\\mathrm{h}}$ .",
        "category": " Materials and methods"
    },
    {
        "id": 9,
        "chunk": "# 2.4. Characterization  \n\nThe contact angles (CAs) of the coatings were determined using a contact angle device (Dataphysics OCA25, Germany). The volume of droplets applied for static contact angle and sliding angle measurements is $4\\upmu\\mathrm{L}$ . An atomic force microscope (AFM, Agilent 5500) was employed to exam the surface roughness of the samples. The morphology of the coated PE and its thicknesses were obtained by field emission scanning electron microscope (FESEM, Hitachi S-4800). Elemental analysis was acquired from the energy dispersive spectroscopy (EDS) device attached to the FESEM. The chemical structures were characterized by Fourier transform infrared (FT-IR) (Thermo Fisher Scientific, USA) at a resolu­ tion of $4\\mathrm{cm}^{-1}$ in the range of $4000{-}500\\mathrm{cm}^{-1}$ . The light transmission of the coating was tested by a Persee TU-1900 UV–Vis spectrophotometer. Optical images of the coatings before and after the self-healing test were taken by an optical microscopy (DM2700P, Leica, Germany). The light source was provided by a Solar Power Meter (PerfectLight, PLMW2000). According to the GB/T31726-2015 standard test method, the antifogging level is divided into level 1 to 5. The antifogging per­ formance test is by placing the sample at $2{\\cdot}3\\ \\mathrm{cm}$ above heated water at $85~^{\\circ}\\mathrm{C}$ for $1\\mathrm{min}$ .  \n\n![](images/943730d16322bad0cc5d5840978babf622b1a8e814c97cdbc560ca898de8f5b9.jpg)  \nFig. 3. a) WCAs after continuous exposure to $365~\\mathrm{{nm}}$ UV irradiation for $^{192\\mathrm{~h~}}$ . Inset pictures show antifogging test surface of coated PE exposed to UV and un­ exposed. b) WCAs were tested under the coated PE was continuously heat treated in an oven $(80~^{\\circ}\\mathrm{C})$ . c) Schematic diagram of sand punching experiment. d) The antifogging grade index of the coating exposed to $_{30\\mathrm{~g~}}$ sands at different scouring heights. Inset image shows the antifogging test surfaces of PSTG film at different scouring heights. e) A plot showing the water contact angles the antifogging grade index of the PSTG coating after exposure to various solvents for 1 h. f) Cross-cut method to measure the adhesion of the film, before the tape was peeled off (top) and after the tape was peeled off (bottom). g) Antifogging test of blank and adherent coating after immersion in various solvents for 1 h. h) Antifogging test of blank and adherent coatings in various temperatures.",
        "category": " Materials and methods"
    },
    {
        "id": 10,
        "chunk": "# 3. Results and discussion",
        "category": " Results and discussion"
    },
    {
        "id": 11,
        "chunk": "# 3.1. Characterization of PSTG coatings  \n\nThe pre-cleaned bare PE was treated with $\\mathbf{O}_{2}$ plasma for 20 s to create it superhydrophilic, as illustrated in Scheme 1. The PSTG solution was uniformly applied on the substrate, using a knife coating method. Strong hydrogen bonds were generated between PVA, SA, $\\mathrm{TiO}_{2}$ , and glycerin during curing at $60~^{\\circ}\\mathrm{C},$ which improved adhesion between the coating and the substrate. Meanwhile, the large amounts of hydrophilic groups in SA and PVA may increase the composite coating’s surface energy.  \n\nThe surface morphology was observed using SEM (Fig. 1a). It can be discovered that $\\mathrm{TiO}_{2}$ was uniformly disseminated in the coating, with just a small quantity of $\\mathrm{TiO}_{2}$ appearing to be agglomerated. The thick­ ness of PSTG composite layer was about $500~\\mathrm{nm}$ . Moreover, the EDS element mapping revealed that the homogeneous solution was uni­ formly coated on PE film (Fig. 1b), with the content of C, Na, O and Ti element of the film being $63.05\\%$ , $34.12\\%$ , $2.54\\%$ , and $0.29\\%$ , respec­ tively (Fig. 1c). The chemical functional groups in PSTG were investi­ gated using FTIR spectroscopy. As shown in Fig. 1d, peaks at $1625\\mathrm{cm}^{-1}$ and $3435~\\mathrm{cm}^{-1}$ correspond to the stretching vibrations of $\\mathsf{C O O-},$ and –OH of SA [40]. Peaks at $1095~\\mathrm{cm}^{-1}$ and $3404~\\mathrm{cm}^{-1}$ correspond to the stretching vibration of C-O, and $-\\mathrm{OH}$ on PVA [41]. Bands at $3416~\\mathrm{cm}^{-1}$ (stretching vibration of –OH) and $672\\mathrm{cm}^{-1}$ (stretching vibration of Ti − O) were also seen in $\\mathrm{TiO}_{2}$ [38]. PSTG coating peaks of –OH, COO– and CO moved to lower wavenumber of $3288~\\mathrm{cm}^{-1}$ , $1413~\\mathrm{cm}^{-1}$ and 1030 $\\mathsf{c m}^{-1}$ , respectively. Moreover, the development of intramolecular or intermolecular hydrogen bonds reduces the chemical bond forces, resulting in a red shift in their vibrational frequencies. As a result, the chemical shifts of these peaks indicate that hydrogen-bonded crosslinking between PSTG coatings has formed [42].  \n\n![](images/bf7f6c3deadabf1fc1f57eac540ff117586c8d12686c67b96f49190bb54e0aa9.jpg)  \nFig. 4. a) Schematic illustration of the self-healing composite coating. b) SEM photographs of the PSTG coating before and after healing. c) UV–Vis transmission spectra of the bare PE and the coated PE after surgical knife cutting and healing. Inset photos show the coated PE after the cutting (left) and after healing (right).  \n\nThe antifogging performance of PSTG, PTG (PVA- $\\mathrm{\\cdotTiO_{2}}$ -glycerin), and STG (SA- $\\mathrm{TiO}_{2}$ -glycerin) were studied to better understand the role of PVA, SA, and $\\mathrm{TiO}_{2},$ as demonstrated by the optical images in Fig. S1a. The images were taken after the samples were placed above the hot water for $1\\mathrm{min}$ , and both the STG and PTG surfaces have a visible fog layer. PSTG, on the other hand, has excellent antifogging performance with no fog layer. In the early stage of antifogging, the cross-linked PSTG was able to absorb the surrounding water vapor quickly, allowing the water vapor to swiftly spread across the surface, and achieve the anti­ fogging performance.  \n\nTo test the role of $\\mathrm{TiO}_{2}$ , $20~\\ensuremath{\\upmu\\mathrm{L}}$ of methyl blue solution $(10\\mathrm{ppm})$ wa dropped onto the coating and then irradiated with $365~\\mathrm{{nm}}$ ultraviolet light $(1.27\\mathrm{\\mW/cm}^{2})$ for $20\\ \\mathrm{min}$ on two samples, PSTG and PSG (Fig. 2a). The color of the methyl blue solution on the PSTG was entirely deteriorated, whereas the color of methyl blue solution on the PSG remained unchanged, demonstrating that the $\\mathrm{TiO}_{2}$ might endow the composite coating with photocatalytic ability. Apart from that, three different sizes of $\\mathrm{TiO}_{2}$ was used in this experiment and all of them exhibited satisfactory photocatalytic performance, while having no negative impact on antifogging performance (Fig. S1b). The PSTG sur­ face had a water contact angle of $66.8^{\\circ}$ , and the coating had excellent antifogging properties (Fig. 2b). The PSTG coating was more transparent than the blank film (Fig. 2c), making it slightly antireflective. The increased light transmittance due to reduced surface scattering could be due to the coating’s substantially reduced surface roughness ( ${\\cdot}{\\sim}10\\ \\mathrm{nm}$ , Fig. S1c).",
        "category": " Results and discussion"
    },
    {
        "id": 12,
        "chunk": "# 3.2. Mechanical property  \n\nContinuous exposure to the UV sources with a wavelength of ${365}\\mathrm{nm}$ and a radiation intensity of $1.27\\mathrm{mW/cm^{2}}$ was used to test the coating’s aging resistance. Even though there was a slight rise in water contact angles (WCAs) after $192\\mathrm{h}$ of UV illumination, which could be attributed to the addition of $\\mathrm{TiO}_{2}$ NPs that act as UV absorbers, the irradiated area had the same excellent antifogging efficacy as the control (Fig. 3a). In contrast, the contact angle of the PSG coating increased significantly and some areas of the coating lost their anti-fogging properties after $192\\mathrm{h}$ of irradiation (Fig. S2). Additionally, the sample was heated in an oven at $80^{\\circ}\\mathrm{C}$ for 17 days to test the hydrophilic coating’s thermal resilience. The coating’s WCAs remained essentially constant after a long heat treat­ ment, and the letters beneath the beaker were plainly visible, indicating excellent antifogging properties (Fig. 3b).  \n\n![](images/1f56a84808c055fbd866b69704e449fdaa5ca4101ec8ea8e667de24ab0090c13.jpg)  \nFig. 5. a) Schematic diagram of self-cleaning of PSTG coating. b) Optical photograph of soybean oil (dyed with oil red) separated from bare PE and coated PE. c) The underwater dynamic sliding angle of coated PE. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)  \n\n![](images/e6ea268c394ca57e3907ab57d86ecb5f06d954b6588967f05d4a6948051b4a03.jpg)  \nFig. 6. a) UV–Vis transmission spectra of the bare PE and the coated PE after freezing at $-23^{\\circ}\\mathrm{C}$ for $24\\mathrm{h}$ . b) The optical photographs of the coated PE and the bare PE after anti-frosting experiment and then exposed to ambient lab conditions for $3\\:s$ .  \n\nFor practical applications, the coating’s mechanical strength is essential. To test the sample’s mechanical stability, as illustrated in Fig. 3c, $\\mathbf{30~g}$ of sands was dropped from a height of 10, 20, 30, $40~\\mathrm{cm}$ respectively, to strike the PSTG coated film [43], and the antifogging level was measured. The film’s antifogging level of the film remained at level 1 even though the impact height increased to $40~\\mathrm{cm}$ (Fig. 3d). Furthermore, the sandpaper abrasion durability of PSTG coating explored. The antifogging performance showed by the insert picture was well maintained in most areas after 100 cycles under $25\\mathrm{{Pa}}$ , although the CAs increased with the increased number of cycles (Fig. S3). The film’s adhesion was further tested using the cross-hatch method, as per the ASTM D3359 standard. No visible debris was observed following the cutting and tape peeling, as shown in Fig. 3f, demonstrating outstanding bonding force between the coating and the substrate. It is also worth noting that the coating performed exceptionally well against fogging in hot water of various temperature (Fig. 3h).  \n\nIn addition, the PE coatings were immersed into several polar and non-polar solvents for 1 h to test the chemical stability of the coating, after which the antifogging grade and hydrophilicity were measured. It was observed that the solvents had no effect on antifogging performance or hydrophilicity, indicating exceptional chemical stability (Fig. 3e, g).  \n\n![](images/fe0e72853ba83ec2e5e80ef7a71f0b3367270e1b3c41459d24fe290d69bb52b1.jpg)  \nFig. 7. a) Schematic diagram of greenhouse film construction. b) Antifogging test blank and adherent coatings after exposure to outdoors for several days. c) WCAs of the coating placed outdoors, where the green area is sunny and the orange area is rainy. d) Schematic diagram of light intensity test. e) Light intensity of blank PE and coated-PE under different hot fogging times. f) The average transmittance of coated PE at different temperatures. g, h) Image of blank (left) and coated (right) greenhouse film after $^\\textrm{\\scriptsize1h}$ of $100^{\\circ}\\mathrm{C}$ hot fogging. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)",
        "category": " Results and discussion"
    },
    {
        "id": 13,
        "chunk": "# 3.3. Self-healing property  \n\nIt is unavoidable that substantial damage to the functional coating occurs consequently, therefore the robust antifogging coating with good self-healing ability is critical for sustainable application. To our superise, the clearly visible scratches were obviously removed via 1 s of water immersing or $5\\mathrm{min}$ of solar light irradiating treatment, indicating the hydrogel coating with good self-healing ability (Fig. 4a, b). This is ascribed to the water molecules adsorbed in the hydrogel coating can interact with the hydroxyl or carboxyl groups of PVA and SA to dynamically restore the broken hydrogen bonds. Furthermore, the transmittance of the self-healed sample was tested to quantitatively analyze the self-healing performances. It was difficult to distinguish between the pristine and self-healed sample (Fig. 4c), which indicated the exceptional self-healing performance made it great potential for practical application. Additionally, a comparison of self-healing condi­ tions with previous work is shown in Table S3, the current work displays simpler conditions and faster self-healing. At the same time, it also shows high light transmittance and excellent anti-fogging performance.",
        "category": " Results and discussion"
    },
    {
        "id": 14,
        "chunk": "# 3.4. Antifouling property  \n\nHydrophilic surfaces are known to have a high surface energy, therefore low surface energy materials, such as various oils, can easily contaminate the surface. Hence, antifouling plays a vital role in a variety of actual applications. As illustrated in Fig. 5a, it is believed that if the water molecules adsorbed on the surface of the PSTG coating can swiftly create a layer of hydration film, the oil droplets will be unable to reach the substrate, providing antifouling via underwater superoleophobicity. When the sample was immersed in water, a soybean oil (dyed with oil red) droplet quickly rolled off the coated surface and floated on the water surface, leaving a clean surface whereas the bare PE was contaminated (Fig. 5b). The underwater oil contact angle on coated PE film was measured using a $4~{\\upmu\\mathrm{L}}$ oil drop (1,2-dichloroethane), which revealed that the oil CA was around $160^{\\circ}(\\mathrm{Fig.~}1\\mathbf{a})$ . Furthermore, the oil droplets easily slipped off the surface of the coating, when the sample stage was oriented to a deviation of $3.3^{\\circ}$ from the horizon, demon­ strating a remarkable superoleophobic effect (Fig. 5c).",
        "category": " Results and discussion"
    },
    {
        "id": 15,
        "chunk": "# 3.5. Anti-freezing property  \n\nThe frost-resistance performance of PSTG coating at extreme cold circumstances was also evaluated in climate areas where typical func­ tional coatings may lose their performance due to low temperatures. The light transmittance variation of PE films with and without PSTG coating frozen at $-23^{\\circ}\\mathsf{C}$ for $24\\mathrm{h}$ were shown in Fig. 6a. The result showed that the transmittance of bare PE declined over time, whereas the modified PE increased light transmission to the same level as the control PE without defrosting. This inspiring result can be attributed to two aspects. First, the coating contains glycerin, which can form hydrogen bond with water and lower its freezing point. Second, PVA has a high capacity for absorbing water, reducing water vapor condensation. The visibility of two samples from $-23^{\\circ}\\mathsf{C}$ to room temperature for 3 s is shown in Fig. 6b. The vapor condensed instantaneously on the bare PE film, obstructing light transmission obstructing, but the coated PE remained good transparent.",
        "category": " Results and discussion"
    },
    {
        "id": 16,
        "chunk": "# 3.6. Versatility and durability  \n\nThe created coating can be applied on a variety of substrates. The coated film had no effect on the substrates’ transmittance, as seen in Fig. S4. The coated glass, PET, PC, and PVC all had a transmittance of at least $82\\%$ . By exposing the samples to hot water vapor at $85~^{\\circ}\\mathrm{C},$ , the antifogging efficacy of the coated substrate was also evaluated (Fig. S5). The substrate without coating fogged up rapidly, whereas the coated substrates did not fog up at all, as previously described.  \n\nIt is also necessary to evaluate the coating’s durability in order to achieve its practicality. The obtained sample was tested for durability by analyzing its water contact angles and antifogging performance in an outdoor environment for many days. The WCAs gradually increased after 18 days (Fig. 7c), but the antifogging level remained at level 1 as shown in Fig. 7b, owing to the adhering of pollutant with a lower relative surface energy. Besides, the antifogging activity can be sus­ tained for more than 5 months in ambient conditions (Fig. S6).  \n\nAs displayed in Fig. 7a, the rising water vapor wetted the greenhouse canopy layer, forming a water film. Any excess water can slide down the slope of the canopy wall to keep the antifogging properties of the PE film. To simulate an agricultural greenhouse, a 0.2 curvature shed with half of the area uncoated for comparison was made. It could be obvi­ ously seen that the blank film was clearly covered with dense water drops, while the coated PE still maintained great transparency (Fig. $^{7}{\\bf g},$ h). Because the ultimate purpose of making antifogging film was to reduce the light refraction while having no influence on photosynthesis, the intensity of light transmission before and after the spraying of water vapor was measured, as shown in Fig. 7d. The light intensity of the blank film reduced significantly, from $1.5\\ \\mathrm{kW/m^{2}}$ to $0.5\\ \\mathrm{kW/m^{2}}$ , while the processed sample showed minor reduction, demonstrating excellent applicability (Fig. 7e). Furthermore, the water vapor temperature is also an indicator to measure the shed film’s practical performance. At tem­ peratures below or above $60~^{\\circ}\\mathrm{C}$ , the coated PE retained a high optical transmittance (over $85\\%$ ) almost independent with time, implying an efficient resistance to fog formation across a wide temperature range, as shown in Fig. 7f.",
        "category": " Results and discussion"
    },
    {
        "id": 17,
        "chunk": "# 4. Conclusions  \n\nIn summary, we have effectively fabricated a multifunctional hy­ drophilic antifogging coating through a convenient, environmentalfriendly and energy-saving one-step technique. The PSTG coating not only had excellent heat resistance but also UV resistance due to the addition of $\\mathrm{TiO}_{2}\\mathrm{NP}s$ . After sand impingement at various heights and $^{\\textrm{1h}}$ of soaking in both polar and non-polar solvent, the coating showed satisfactory mechanical and chemical stability, and maintained a level 1 antifogging rating. After being frozen at $-23^{\\circ}\\mathsf{C}$ for $24\\mathrm{~h~}$ and placed under ambient conditions for 153 days. Surprisingly, the sample showed excellent weather resistance. Additionally, it also had a high rate of selfhealing and a good antifouling action. The novel approach also proved universality, opening up a new path for long-lasting agricultural anti­ fogging coatings with commercial potential.",
        "category": " Conclusions"
    },
    {
        "id": 18,
        "chunk": "# Declaration of Competing Interest  \n\nThe authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.",
        "category": " Results and discussion"
    },
    {
        "id": 19,
        "chunk": "# Data availability  \n\nData will be made available on request.",
        "category": " References"
    },
    {
        "id": 20,
        "chunk": "# Acknowledgements  \n\nThe authors thank Natural Science Funds for Distinguished Young Scholar of Fujian Province (2020 J06038), Natural Science Foundation of Fujian Province (2019 J01652, 2019 J01256), National Natural Sci­ ence Foundation of China (22075046, 51972063), and 111 Project (No. D17005).",
        "category": " References"
    },
    {
        "id": 21,
        "chunk": "# Appendix A. Supplementary data  \n\nSupplementary data to this article can be found online at https://doi. org/10.1016/j.cej.2022.137879.",
        "category": " References"
    },
    {
        "id": 22,
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