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"chunk": "# Transparent and Scratch-Resistant Antifogging Coatings with Rapid Self-Healing Capability \n\nBang Liang,†,‡ Zhenxing Zhong,†,‡ Erna Jia,†,‡ Guangyu Zhang,\\*,† and Zhaohui Su\\*,†,‡ \n\n†State Key Laboratory of Polymer Physics and Chemistry, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, \nChangchun 130022, P. R. China \n‡University of Science and Technology of China, Hefei 230026, P. R. China \n\nSupporting Information \n\nABSTRACT: Typical antifogging coatings based on hydrophilic polymers are soft and susceptible to mechanical damage. In this paper, an antifogging coating that is both scratch-resistant and self-healing is fabricated by copolymerizing sulfobetaine methacrylate and 2-hydroxyethyl methacrylate in the presence of sulfobetaine-modified silica nanoparticles in one pot. The coating is highly efficient in preventing fog formation at the surface and reducing ice adhesion, and is resistant to fouling by oil and protein, due to the strong hydration ability of the zwitterionic moieties. The composite coating is resistant to scratching and abrasion under normal use conditions to maintain its transparency due to increased hardness by the filled silica nanoparticles and is able to heal completely within several minutes severe scratches and cuts inflicted in harsh conditions, owing to the water-assisted reversibility of the electrostatic and hydrogen-bonding interactions holding together the polymer components and the silica nanoparticles. The multiple desirable properties demonstrated and the simple fabrication process of the coating offers great potential in many practical applications. \n\n \n\nKEYWORDS: antifogging, transparent, scratch-resistant, self-healing, antifouling",
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"category": " Abstract"
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"id": 2,
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"chunk": "# INTRODUCTION \n\nFogging on transparent substrates such as automobile windshields, eyeglasses, and medical/analytical instrument lenses results in significant scattering of visible light and thus reduces light transmission through the substrates, which can cause inconvenience and even adverse consequences in practical applications.1−5 Over the past decade, extensive research has been carried out in order to prevent fogging on the substrates. Among the various approaches reported, one effective strategy is constructing a thin hydrophilic polymer coating on the surface of the transparent substrate, for example poly(ethylene glycol) (PEG),3 acrylic polymers,6 and polymeric quaternary ammonium salts,7 which can effectively prevent fog formation by spreading the condensed water droplets into a thin continuous water film. However, these hydrophilic polymer-based antifogging coatings are soft and susceptible to mechanical damage such as scratching and abrasion, leading to deteriorating transparency and antifogging properties.8 In order to solve this problem, research effort has been focused on endowing the polymeric coating with selfrepairing character, so that the coating can recover its transparency and hydrophilicity after being damaged.8−11 Self-healing materials can recover damaged structure and functions autonomously with external stimuli.12,13 While extrinsic self-healing materials require an embedded external healing component for repair, intrinsic self-healing materials interactions14−17 or dynamic covalent bonds,18−21 providing a can repair the damage via inherent reversible noncovalent practical and convenient avenue to construct thin films with self-healing ability. Recently, self-healing polymeric antifogging coatings have been reported by several groups. For instance, Sun et al. demonstrated that antifogging films based on thick polyelectrolyte multilayer (PEM) assembly10,11 and homogeneous hydrophilic polymeric complexes8 can quickly heal cuts and scratches autonomously in the presence of water. Hozumi et al. prepared antifogging coatings from simple mixtures of polyvinylpyrrolidone and aminopropyl-functionalized nanoclay platelets, and showed that they can heal cuts readily by absorbing water from humid air.9 However, these materials usually are composed of soft building blocks held together by relatively weak interactions in order to achieve high mobility to facilitate the healing process, and as a result self-healing coatings tend to be soft and lack mechanical robustness and long-term durability.22,23 It is well known that inorganic nanofillers can effectively enhance the mechanical strength of polymer material, and this idea has been adopted to improve the scratch-resistance of polymer films.24−26 Recently, Sun et al. introduced $\\mathbf{CaCO}_{3}$ nanoparticles into PEM film assembled from poly(acrylic acid) and poly(ethylenimine) and demonstrated that the nanoparticles can render the healable film more robust and scratch-resistant.27 Despite the progress, fabrication of coatings with good scratch-resistant and self-healing properties is still a challenging task because the dynamic healing based on weak interactions is compromised when strong interactions are introduced to enhance the hardness necessary for scratch-resistance,23,28,29 and in particular, development of a robust antifogging coating remains to be explored. In addition, antifogging coatings in general are high in surface energy and therefore are susceptible to contamination and loss of their antifogging property. Consequently, antifouling property must be considered in the design and fabrication of next-generation antifogging coatings.3 .30 \n\n \nFigure 1. Schematic illustration of the scratch-resistant and self-healing composite coating. \n\n \nFigure 2. $(\\mathsf{a},\\mathsf{b})$ TEM images of $\\mathrm{\\p(SBMA_{7}\\mathrm{-co-HEMA_{3}},}$ ) filled with $5.0\\mathrm{wt}\\%$ (a) plain and (b) modified silica nanoparticles, respectively. (c) UV−vis spectra of the $\\mathrm{\\p(SBMA_{7}\\mathrm{-}c o\\mathrm{-}H E M A_{3})}$ ) coatings filled with silica nanoparticles. (d) FTIR spectra of $\\mathsf{p}(\\mathsf{S B M A}_{7}\\mathsf{-c o-H E M A}_{3})$ with and without modified silica nanoparticles in comparison with that of $\\mathrm{{\\ttpSBMA}}.$ \n\n \nFigure 3. (a) Antifogging performance of a $\\mathsf{p}(\\mathrm{SBMA}_{7^{-}}\\mathrm{co}\\mathrm{-}\\mathrm{HEMA}_{3})$ ) coating filled with $5.0\\mathrm{\\mt\\\\%}$ silica nanoparticles. (b) FTIR spectra of the coating as prepared and after the antifogging test. (c) Time profiles (three independent tests) of ice adhesion strength on a coated glass. (d) Average ice adhesion strength on a coated glass compared with that on a bare glass. \n\nIn this work, we report a self-healing antifogging coating based on polyzwitterion copolymer reinforced by silica nanoparticles. The composite is easily prepared in one pot, and by varying the co-monomer ratio we can readily tune the interactions among the polymer components and the silica nanoparticles, producing a coating that can both resist typical scratching and abrasion to maintain its transparency, and quickly repair severe damages inflicted in harsh conditions. The transparent coating is highly efficient in preventing fogging and reducing ice adhesion and is resistant to fouling by oil and protein.",
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"category": " Introduction"
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"id": 3,
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"chunk": "# RESULTS AND DISCUSSION \n\nThe simple coating fabrication process is schematically illustrated in Figure 1. The coating was synthesized by free radical solution polymerization. Silica nanoparticles were added to increase the hardness of the transparent coating. However, when plain silica particles were used directly, the nanoparticles aggregated in the polymer matrix, resulting in significant scattering and reduction of optical transparency (Figure 2c). To improve the dispersion of silica nanoparticles in the aqueous system, their surfaces were first modified with a hydrophilic silane coupling agent carrying a sulfobetaine group (SI, Figure S1).31 The sulfobetaine groups introduced to the surface can increase the hydrophilicity of the nanoparticles and reduce their aggregation via the stable water layer around the surface.31 The modified silica nanoparticles were well dispersed in an aqueous solution of the hydrophilic monomers, sulfobetaine methacrylate (SBMA) and 2-hydroxyethyl methacrylate (HEMA) with a 7:3 mole ratio, and the polymerization was carried out at $25^{\\circ}\\mathrm{C}$ for $20\\mathrm{min}$ to obtain a viscosity suitable for spin-coating, and the mixture was then spin-coated on the substrate and cured by heating at $80~^{\\circ}\\mathrm{C}$ for $^{2\\mathrm{~h~}}$ to complete the polymerization to produce a clear coating (coded $\\mathsf{p}(\\mathsf{S B M A}_{7^{-}}\\mathsf{c o}{\\mathrm{-}}\\mathrm{HEMA}_{3})$ herein). Figure 2b displays transmission electron microscopic (TEM) images of the coating filled with silica nanoparticles (5.0 wt $\\%$ relative to the polymer), which show uniform distribution of the modified nanoparticles in the polymer matrix, in contrast to the severe aggregation observed for the plain silica nanoparticles. Apparently, the sulfobetaine moieties grafted to the silica nanoparticles have significantly improved their compatibility with the matrix via the electrostatic and dipole interactions with the same sulfobetaine groups of the polymer.32,33 As seen in Figure 2c, a glass slide with a $\\mathsf{p}(\\mathrm{SBMA}_{7}\\mathrm{-co-HEMA}_{3})$ composite coating of ${\\sim}3.8\\ \\mu\\mathrm{m}$ thickness (SI, Figure S2) containing 5.0 wt $\\%$ silica nanoparticles exhibits $\\sim90\\%$ transmittance in the entire visible region, almost identical to that of the uncoated one, showing excellent transparency of the coating. \n\nFigure 2d shows FTIR spectrum of the composite coating, which exhibits absorption peaks at ${\\sim}1710$ and ${\\sim}1480~\\mathrm{cm}^{-1}$ corresponding to the $\\scriptstyle{\\mathrm{C}}={\\mathrm{O}}$ stretching and the $\\mathrm{CH}_{3}$ bending of the SBMA unit, respectively.34 More interestingly, the strong ${S0}_{3}^{-}$ stretching peak, observed at ${\\sim}1034~\\mathrm{cm}^{-1}$ for SBMA homopolymer $(\\mathrm{pSBMA}),^{35}$ is found to shift to a lower frequency of ${\\sim}1028~\\mathrm{cm}^{-1}$ for the copolymer composite. This shift is ascribed to hydrogen-bonding interactions between the sulfonate group in the sulfobetaine unit and the hydroxyl group in the HEMA unit.34 This provides evidence of additional interactions besides the electrostatic and dipole interactions among the polymeric components and the modified silica nanoparticles, as schematically illustrated in Figure 1, which help stabilize the dispersion of the nanoparticles in the system25,27 and facilitate the self-healing of the film, as we will discuss later. \n\n \nFigure 4. (a) Photograph of a $\\begin{array}{r l}{\\lefteqn{\\operatorname{p}\\big(\\mathrm{SBMA}_{7^{-}}\\mathrm{co}{\\mathrm{-}}\\mathrm{HEMA}_{3}\\big)}\\quad}&{{}}\\end{array}$ coating filled with 5.0 wt $\\%$ modified silica nanoparticles (right) and an unfilled one (left) after 500 abrasion cycles, and (b) UV−vis spectra of the two coatings before and after the abrasion test. \n\nTo investigate the adhesion between the coating and the substrate, a cross-tape test was conducted according to the ASTM D3359 standard.36 No detachment of the coating or debris was observed under optical microscope (SI, Figure S4), which indicates a highest level of adhesion (5B) between the coating and the substrate by the ASTM standard, attributed to the stable covalent bonds between the coating and the substrate, as well as good mechanical integrity and strength of the coating due to its strengthened cross-linking network structure. These structural characteristics also endow the superhydrophilic coating with excellent stability and adhesion to the substrate in aqueous environment (SI, Figure S4). \n\nNext, the antifogging property of the composite coating was examined. Two glass slides, one bare and the other coated, were first stored in a freezer at $-20{}^{\\circ}\\mathrm{C}$ and then exposed to the atmosphere at room temperature. As shown in Figure 3a, the bare glass fogged in a few seconds, and the alphabets behind the glass were blurred due to the scattering of light by the water droplets condensed on the glass, whereas the coated glass remained clear, and the alphabets behind the glass were highly visible, confirming the excellent antifogging property of the coating. Figure 3b compares FTIR spectra of a composite coating recorded before and after the antifogging test, respectively. The broad OH stretching band at ${\\sim}3450~\\mathrm{cm^{-1}}$ increases dramatically, and the OH bending at $\\sim1640~\\mathrm{cm^{-1}}$ also becomes more intense, suggesting the absorption of a large amount of water by the coating. By gravimetric analysis, the mass increase of the coating was found to be ${\\sim}40\\%$ . As a reference, the coating can absorb up to $\\sim160\\%$ water when immersed in water for $^{24\\ \\mathrm{h},}$ showing outstanding hydration ability of the polymer. Obviously, the polyzwitterion-based coating can quickly absorb water molecules from the environment to form a highly hydrated layer at the surface, making it superhydrophilic,37,38 and subsequently condensed water spreads completely on this surface and no droplets are formed. In fact, upon direct exposure to the spray produced by a humidifier for extended periods of time, the coating was found to suppress fog formation and exhibit the same optical transparency (SI, Figure S5). Moreover, water molecules absorbed from the atmosphere by the polyzwitterion-based coating largely exist as bound water, which maintains a liquidlike state even at low temperatures and can act as a selflubricating interfacial layer to reduce ice adhesion.39 Figure 3c presents typical profiles of ice adhesion strength versus time, which shows that the ice adhesion strength increases quickly to a maximum value and then abruptly drops to zero when the ice is detached from the surface. The maximum value of the curve is defined as the ice adhesion strength according to the characteristic of cohesive breakage.39−41 As shown in Figure 3d, the coated glass exhibits a much lower ice adhesion strength of $62~\\mathrm{KPa}$ as compared with that for bare glass (245 KPa) (SI, Figure S6), indicating that the coating is an excellent material for anti-icing application as well.42 \n\nScratch-resistance is an important property for coatings, especially for the ones for optical applications. The hardness of the coatings prepared with various silica nanoparticle contents were assessed by a pencil hardness test on the basis of the ASTM D3363 standard,43 using pencils ranging from 6B (the softest) to 6H (the hardest) (SI, Figure S7). The unfilled $\\mathsf{p}(\\mathsf{S B M A}_{7^{-}}\\mathsf{c o}\\mathrm{-HEMA}_{3})$ coating was rather soft, with a pencil hardness of HB, whereas the ones reinforced with 2.5 and 5.0 wt $\\%$ silica exhibited significantly enhanced hardness of 2H and 4H, respectively. The latter was chosen for a further scratchresistance experiment, where the coatings were subjected to repeated abrasion using a cylindrical metal (with a weight of $_{500\\mathrm{~g)}}$ whose bottom was covered with a piece of ramie cloth,25,27 and the results are presented in Figure 4a. After 500 abrasion cycles, the unfilled $\\mathrm{p}(\\mathrm{SBMA}_{7^{-}}\\mathrm{co}{\\cdot}\\mathrm{HEMA}_{3})$ coating was heavily damaged, with numerous grooves clearly observed at the surface, and the optical transparency of the coating as measured by UV−vis spectroscopy was greatly reduced, with the transmittance at $550~\\mathrm{nm}$ decreasing from ${\\sim}90\\%$ to $60\\%$ . Meanwhile, after the same treatment, no visible scratches were identified on the surface of the coating containing 5.0 wt $\\%$ modified silica nanoparticles, and the transparency remained the same before and after the test, with a transmittance of $\\sim90\\%$ at $550~\\mathrm{nm}$ (Figure 4b). These two experiments clearly demonstrate that the modified silica nanoparticles added to the polyzwitterion coating can significantly enhance its hardness without compromising the optical transparency, and endow the coating with scratch-resistance ability that is adequate for handling mild abrasions in daily application settings. \n\nNevertheless, the coating in use may accidentally be damaged by some harder objects, and the scratches inflicted would strongly reduce the transparency of the coating. This issue can be resolved if the coating can repair the damages autonomously to recover its original properties. To simulate use under harsh conditions, the $\\mathsf{p}\\big(\\mathrm{SBMA}_{7}\\mathrm{-co-HEMA}_{3}\\big)$ composite coating (with 5.0 wt $\\%$ silica) was rubbed repeatedly with a piece of 2000-grit sandpaper. Numerous shallow grooves appeared on the scratched coating, and the alphabets behind the coated glass became unclear, and the transmittance at $550~\\mathrm{nm}$ decreased from $90\\%$ to $70\\%$ . Then, the coating was dipped into deionized water for mere 2 s and quickly removed. \n\n \nFigure 5. (a) Optical microscopic images (left) and photographs (right) of the $\\begin{array}{r}{\\mathrm{p}(\\mathrm{SBMA}_{7^{-}}\\mathrm{co}{\\mathrm{-}}\\mathrm{HEMA}_{3})}\\end{array}$ ) coating filled with 5.0 wt $\\%$ silica before (top) and after healing (bottom). (b) UV−vis spectra of the composite coating as-prepared, scratched, and healed. (c) Photographs (left) and optical microscopic images (right) of the damaged (top) and healed coating (bottom) (scale bars: $50\\mu\\mathrm{m}\\mathrm{,}$ ). (d) Healing of coatings of copolymers with 0, 15, and 30 mol $\\%$ HEMA, respectively (from left to right; scale bars: $50~\\mu\\mathrm{m}\\mathrm{\\ddot{\\Omega}}$ ). \n\nWithin $2\\ \\mathrm{min}$ in lab environment at room temperature, the scratches on the coating surface completely disappeared, and the alphabets behind the coated glass became clear again, with the transmittance at $550~\\mathrm{nm}$ recovering to $90\\%$ , showing rapid self-healing ability of the coating assisted by water (Figure 5 a,b). \n\nOccasionally severe damages can occur, so the healing ability of the coating under such circumstances was also investigated. A cut of ${\\sim}250~\\mu\\mathrm{m}$ width in the coating was made by a blade, exposing the underlying glass substrate. Again, the damaged film was dipped into deionized water for 2 s and then allowed to heal in lab environmentat room temperature, and within 6 min the scar disappeared completely and the transparency was recovered (Figure 5c). The cutting/healing cycle was repeated at the same location for 20 times (when the experiment was terminated), and the coating was found to completely recover its surface appearance, composition, and hardness at the damaged location after healing (SI, Figure S8). Considering that a film so thin $(3.8\\mu\\mathrm{m})$ can heal scars of a width more than 65 times of its thickness so quickly and so many times, its ability to repair large structural damages is truly amazing. In fact, thicker films can self-heal even faster (SI, Figure S9). For example, at $22.5~\\mu\\mathrm{m}$ thickness the coating can repair a cut of the same width within $2.5\\ \\mathrm{min}$ . This is because in thicker films, more polymer segments are available to relocate to the damaged section and to fill the void created by the damage.9,10,44 By the same token, thinner coatings are expected to heal more slowly and may not be able to repair large damages completely when the thickness is further reduced. But their antifogging and scratch-resistance properties should be the same, because the polyzwitterion film remains superhydrophilic at several tens of nanometer thickness,39 and the silica nanoparticles that render the coating scratch-resistant are only $30\\ \\mathrm{nm}$ in diameter. \n\nIn order to explore the healing mechanism, the polyzwitterion coatings loaded with 5.0 wt $\\%$ silica nanoparticles and of the same thickness $(3.8~\\mu\\mathrm{m})$ but different HEMA contents were prepared, and subjected to the same cut-and-heal test. The cut in the pSBMA coating, which contained no HEMA units, recovered only partially after $^{10\\mathrm{~h~}}$ showing rather weak healability of the homopolymer. Replacing $15\\mathrm{\\mol\\}\\%$ of the SBMA units with HEMA, the $\\mathrm{\\Omega_{3}(S B M A_{8.5}–c o–H E M A_{1.5})}$ coating repaired the scar completely in $30~\\mathrm{\\min}$ . Further increasing the HEMA content to $30\\mathrm{\\mol\\\\%},$ , the $\\mathsf{p}(\\mathsf{S B M A}_{7}{\\mathsf{-c o-}}$ $\\begin{array}{r}{\\mathrm{HEMA}_{3}.}\\end{array}$ ) coating completely healed the damage in $6~\\mathrm{min},$ , as described above. Finally, a $\\mathsf{\\Omega}_{\\mathrm{p}}({\\mathrm{SBMA}}_{\\mathrm{7}}{\\mathrm{-co-HEMA}}_{3})$ coating containing no silica nanoparticles was found to heal its scar even slightly faster, in $\\textsf{S}_{\\operatorname*{min}}$ (Figure 5d). As illustrated in Figure 1, electrostatic interactions and hydrogen-bonding are the major forces holding together the linear polymer chains as well as the sulfobetaine-modified nanoparticles, which exhibit strong reversibility with the assistance of water, endowing the material with water-facilitated healing ability.34,44 Upon exposure to water, the damaged coating can absorb a large quantity of water molecules to weaken the electrostatic and the hydrogen-bonding interactions among its components to increase their mobility. Moreover, hydrogen-bonding interactions among the components are more susceptible to water disruption than electrostatic interactions.45 Therefore, the copolymer with a higher HEMA (the only hydrogen-bond donor in the system) content is weakened to a greater extent by water molecules absorbed, resulting in higher mobility of the components and hence improved healability of the coating. Then, in the healing process, the mobile polymer chains and the nanoparticles in the hydrated coating migrate to the damaged region due to the difference in chemical potential, where the electrostatic and hydrogen-bonding interactions reform, repairing the damages in the coating. Meanwhile, the optical transparency and antifogging performance of the coating was not affected by the copolymer composition (SI, Figure S10), because both SBMA and HEMA polymers are amorphous and hydrophilic. The hardness of the coating was not impacted either by the SBMA/HEMA ratio (SI, Table S1) since it mainly depends on the silica content. It should be pointed out that further increasing the HEMA content, although benefits the healability, can weaken the coating when immersed in water to such extent that the coating may fall apart. \n\n \nFigure 6. (a) Snapshots showing a soybean oil droplet sticks on bare glass (top) but is lifted on a glass coated with $\\mathsf{p}(\\mathrm{SBMA}_{7^{-}}\\mathrm{co}{\\mathrm{-}}\\mathrm{HEMA}_{3})$ with 5.0 wt $\\%$ modified silica (bottom) after immersion in water. (b) Mass of bovine serum albumin adsorbed on a bare Au electrode and a coated one. \n\nFinally, the antifouling property of the coating was evaluated. In general, due to their high surface energy, hydrophilic surfaces are easily stained by the low surface energy contaminants, such as various oils and biological species.30 As seen in Figure 6a, soybean oil easily wet both bare glass slide and the $\\mathrm{p}(\\mathrm{SBMA_{7}{\\mathrm{-}}c o{\\mathrm{-}}H E M A_{3})}$ coating, contaminating the hydrophilic surfaces in a similar way. When the stained surfaces were placed in contact with water, however, the oil staining the $\\mathsf{p}(\\mathsf{S B M A}_{7^{-}}\\mathsf{c o}\\mathrm{-HEMA}_{3})$ coating was quickly lifted and removed completely from the surface, showing excellent antifouling performance by the coating, whereas the one on bare glass remained. This can be attributed to the strong waterbinding ability of the zwitterionic groups.46 In addition, the $\\mathrm{p}(\\mathrm{SBMA}_{7}\\mathrm{-co-HEMA}_{3})$ composite coating is resistant to biofouling. Protein adsorption on a coated substrate was found to be reduced by more than two thirds compared with that on a bare Au electrode (Figure 6b and Figure S11). The favorable protein resistance property of the coating is again due to the strong hydration ability of the zwitterionic groups, which can interact with water molecules and form a dense quasiliquid water layer, efficiently preventing protein adhesion to the surface.47,48 Furthermore, we found that the antifouling ability of the coating is lost when the coating is scratched extensively and can be readily recovered upon healing (SI, Figure S12), again demonstrating excellent healing ability of the coating.",
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"chunk": "# CONCLUSIONS \n\nIn summary, we have demonstrated a robust and transparent antifogging coating based on a polyzwitterion copolymer reinforced by silica nanoparticles. The silica nanoparticles were modified with sulfobetaine moieties to not only improve dispersion of the nanoparticles in the hydrophilic polymer matrix, but also make them reversible cross-linking points. By tuning the electrostatic and hydrogen-bonding interactions among the polymer components and the silica nanoparticles, we obtained a coating that is able to resist scratching and abrasion under normal use conditions to maintain its transparency, as well as rapidly repair severe damages inflicted in harsh conditions to restore its functions. The transparent coating is highly efficient in preventing fogging at the surface and reducing ice adhesion, and is resistant to fouling by oil and protein, due to the strong hydration ability of the zwitterionic moieties. The coating material can be easily prepared in one pot and cast on the substrate with good adhesion, showing great potential in commercial application.",
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"category": " Conclusions"
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"chunk": "# EXPERIMENTAL SECTION \n\nMaterials. Sulfobetaine methacrylate (SBMA), γ-methacryloxypropyl trimethoxysilane (MPSi), and 1,3-propane sultone were obtained from Energy Chemical Co., Ltd. Silica nanoparticles (average diameter of $30\\ \\mathrm{nm}$ ) were purchased from Xiya Chemical Reagents Company. (N,N-dimethyl-3-aminopropyl)trimethoxysilane (DMASi), ammonium persulfate, and 2-hydroxyethyl methacrylate (HEMA) were purchased from J&K Chemical Co., Ltd. Acetone, sodium phosphate, potassium dihydrogen phosphate, sodium chloride, potassium chloride, toluene, and sodium metasulfite were purchased from Beijing Chemical Reagents Company. Bovine serum albumin (BSA) was purchased from Shanghai Sangon Biotechnology Co., Ltd. Soybean oil was purchased from a local supermarket. Water used in all experiments was produced by a PGeneral GWA-UN4 purification system ( $18.2~\\mathrm{M}\\Omega{\\cdot}\\mathrm{cm}$ resistivity). \n\nInstruments and Characterization. Film thickness was measured on the KLA-Tencor P-117/P-7 profiler. UV−vis spectra were acquired on a TU1901 spectrometer (Beijing Purkinje General Instrument Co., Ltd). FTIR spectra were recorded on a Nicolet 870 infrared spectrometer equipped with a smart ATR accessory with 256 scans at a resolution of $\\bar{2}\\mathrm{cm}^{-1}$ . Optical micrographs were obtained on a polarized optical microscope (Leica DLMP, GER). Morphology of nanoparticles in the coatings was observed on a TEM (Hitachi model H-900). Protein adsorption was analyzed using a quartz crystal microbalance with dissipation (QCM-D, E1, Q-Sense, Sweden) equipped with an AT-cut quartz crystal resonator. \n\nSurface Modification of the Silica Nanoparticles. Silica nanoparticles were modified as described in the literature.31 First, 3- [dimethyl(3-(trimethoxysilyl)propyl)ammonio]propane-1-sulfonate (SBS) was synthesized. Briefly, DMASi $\\left(5.0\\ \\mathrm{g},24\\ \\mathrm{mmol}\\right)$ and 1,3- propane sultone $(3.0~\\mathrm{~g},~25~\\mathrm{~mmol})$ were dissolved in $25~\\mathrm{\\mL}$ of anhydrous acetone under nitrogen, and the mixture was stirred for 6 h. The white precipitate was collected and dried at room temperature with a yield of $90.5\\%$ . Silica nanoparticles $\\left(50\\mathrm{mg}\\right)$ were sonicated in 5 $\\mathrm{mL}$ of water for $30\\ \\mathrm{min}$ Then, $9.5~\\mathrm{mg}$ of SBS were added to the mixture, which was stirred constantly for $^{6\\mathrm{~h~}}$ at $80~^{\\circ}\\mathrm{C}.$ . Next, the mixture was centrifuged at ${5000}~\\mathrm{rpm}$ for $30~\\mathrm{min}$ and the centrifugate was collected and washed three times with deionized water to remove the physically adsorbed molecules. The final centrifugate was dried at $80~^{\\circ}\\mathrm{C}$ and stored under vacuum. \n\nFabrication of the $\\mathsf{P}(\\mathsf{S B M A}_{7}\\mathsf{-c o-H E M A}_{3})$ Coating. The substrates were first cleaned with boiling piranha solution (7:3, $98\\%$ $\\mathrm{H}_{2}S\\mathrm{O}_{4}{:}30\\%\\ \\mathrm{H}_{2}\\mathrm{O}_{2})$ for $^\\mathrm{~1~h~}$ and then rinsed with water and dried under nitrogen. The freshly cleaned substrates were then immersed in an MPSi solution in anhydrous toluene $\\left(1{:}60,{\\bf v/v}\\right)$ at $80~^{\\circ}\\mathrm{C}$ for $^{2\\mathrm{~h,~}}$ rinsed with toluene to remove the physically adsorbed molecules and dried with a stream of nitrogen. Silica nanoparticles (2.5 or 5.0 wt $\\%$ relative to the total mass of SBMA and HEMA) were sonicated in 2.5 mL of water for $20~\\mathrm{min},$ and a mixture of SBMA/HEMA (7/3 mole ratio), ammonium persulfate $(1.0\\mathrm{mol}\\%)$ and sodium metasulfite (0.5 mol $\\%$ ) was added. The solution was stirred at $25~^{\\circ}\\mathrm{C}$ to allow the polymerization to proceed for $20~\\mathrm{min}.$ , and then spin-cast on the pretreated substrate. The coating was heated at $80~^{\\circ}\\mathrm{C}$ for $^{2\\mathrm{h}}$ to complete the polymerization and the bonding between the coating and the MPSi-modified substrate. \n\nCoating Property Evaluation. The antifogging property was assessed by placing the specimens in a freezer maintained at $-20~^{\\circ}\\mathrm{C}$ for 1 h before exposing them to the atmosphere $\\sim30\\%$ relative humidity) at room temperature. The anti-icing performance was evaluated by the ice adhesion strength measurements as described in the literature.39,50 Hardness was estimated according to ASTM D3363 standard using pencils of a hardness ranging from 6B to 6H. A pencil was selected to mark a line on the specimen. If a scratch was left on the surface by this pencil, it would be replaced with a softer one and the test repeated until no scratch was left on the coating, and the hardness of the last pencil used was considered as the “pencil hardness” of the coating. The scratch-resistance performance of a surface was evaluated by rubbing it repeatedly with a cylindrical metal covered with a piece of ramie cloth at a pressure of $12\\ \\mathrm{KPa}$ .",
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"category": " Materials and methods"
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"id": 6,
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"chunk": "# ASSOCIATED CONTENT",
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"category": " References"
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"id": 7,
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"chunk": "# $\\otimes$ Supporting Information \n\nThe Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acsami.9b09610. \n\nNMR spectrum of SBS, FTIR of bare and modified silica, thickness of the coating, TEM images of the coating filled with different silica nanoparticles, XPS of the coating, optical micrograph of the coating after cross-tape test, coating stability in water, antifogging performance at long exposure time, ice adhesion strength of bare glass, photographs of pencil hardness tester, healing of repeated damage at the same region, healing time as a function of coating thickness, antifogging performance of coating with different copolymer composition, and more antifouling data (PDF)",
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"category": " Results and discussion"
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"id": 8,
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"chunk": "# AUTHOR INFORMATION \n\nCorresponding Authors $^{*}\\mathrm{E}$ -mail: zhanggy608@ciac.ac.cn (G.Z.). $^*\\mathrm{E}$ -mail: zhsu@ciac.ac.cn (Z.S.). \n\nORCID \n\nZhaohui Su: 0000-0002-1530-8142",
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"category": " References"
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"id": 9,
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"chunk": "# Author Contributions \n\nAll authors have given approval to the final version of manuscript.",
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"category": " Abstract/Introduction/Materials and methods/Results and discussion/Conclusions/References"
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"chunk": "# Notes \n\nThe authors declare no competing financial interest.",
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"category": " Conclusions"
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"id": 11,
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