[
    {
        "id": 1,
        "chunk": "# A novel organic-inorganic zwitterionic acrylate polymer for highperformance anti-fog coating  \n\nZiyang Zhenga, Yuping Liua,\\*, Li Wangb,\\*, Li $\\mathtt{Y u}^{\\mathrm{a}}$ , Yuan Cena, Tingting Zhua, Danmei $\\mathtt{Y u}^{\\mathrm{a}}$ , Changguo Chena  \n\na School of Chemistry and Chemical Engineering, Chongqing University, Chongqing, 400044, China b Cccc-Aecom Eco-Environmental Corporation Limited., Beijing, 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: Anti-fog coating Low temperature Zwitterionic salt Hydrophilicity  \n\nA novel organic-inorganic zwitterionic polymer was developed via free radical copolymerization using quaternary ammonium salt as hydrophilic monomer. The unique structure realizes the perfect compromise between the hydrophobicity and hydrophilicity. The chemical composition, the physical properties, the anti-fog characteristic and mechanism of the zwitterionic acrylate coating were investigated by FT-IR, UV-VIS spectrometry, XPS, AFM and water contact angle. After anti-fogging test under ultralow temperature at $\\mathrm{-40^{\\circ}C}$ , the resultant zwitterionic acrylate polymer displays high transparency of $91\\%$ significantly better than that of the bare PC board $21\\ \\%$ . AFM images and water contact angle test demonstrate that the hydrophilic (the soft) region is continuously distributed on the surface of SMA-H coating with smaller water contact angle of $10^{\\circ}$ , indicates better hydrophilicity and wettability. The organic-inorganic zwitterionic polymer endows the coating on polycarbonate (PC) substrate with excellent anti-fog/frost performance, good adhesion and stability (repeated use for 100 times) under wider temperature range $(-40\\sim80^{\\circ}\\mathrm{C})$ of applications.",
        "category": " Abstract"
    },
    {
        "id": 4,
        "chunk": "# 1. Introduction  \n\nPolycarbonate (PC) has been extensively used in our daily life due to its excellent transmittance and weather ability [1,2]. However, fogging frequently occurs on the surface of transparent material PC when the temperature of the surrounding solid surface falls below the dew point of contained-water vapor air at certain relative humidity. The undesirable phenomenon means water vapor condensing onto the solid surface under high or low temperature, such as windshield glass, mirror, goggle, cameras, sensors, windows, photovoltaic modules, endoscopes and so on [3,4]. The condensation gives rise to a series of inconvenient and detrimental problems, involving in blurred vision, light scattering, energy consumption and safety hazard during the usage process of transparent glass and plastics [5,6].One strategy to solve these problems is surface modification with hydrophilic anti-fog coating [7,8]. On the surface of hydrophilic anti-fog coating, the water droplets spread over the whole solid surface as a sheet-like water layer, favorable for light transmittance without scattering [9,10]. Generally speaking, the interfacial energy falls to a minimum value once the water droplets are condensed [11,12]. According to Young’s equation, the hydrophilicity of solid surface can be characterized by the contact angle between the three-phase interfaces [13,14]. The contact angles of the superhydrophilic and hydrophilic surfaces feature the range of $5^{\\circ}<\\theta<10^{\\circ}$ and $10^{\\circ}<\\theta<40{-}50^{\\circ}$ , respectively. Then, developing a stable hydrophilic coating with versatile functionalities and facile process is essential for its practical application in hydrophilic anti-fog coating.  \n\nMore recently, many efforts have been reported on synthesizing the hydrophilic coating with good transmittance and anti-fog performance [15,16]. Maechler et al. successfully assembled a multilayer transparent PVA hydrophilic anti-fog coating on a polycarbonate (PC), but its stability should be further improved to practical application [17]. Nuraje et al. produced good mechanical and durable, and long-lasting anti-fog coatings with polysaccharides [18]. Cebeci et al. prepared stably superhydrophilic films with silica nanoparticles and a polycation by the layer-by-layer method [19]. A special hydrophilic/hydrophobic bilayer material with tween-20 and dipentaethritol hexaacrylate was developed by Chang et al. [20]. Further, an effective UV curable hydrophilic acrylate polymers containing a sulfonic acid group was reported as an anti-fog coating by Yuan [4]. Valuably, the zwitterionic polymers raises a lot of concerns comparing to conventional polymers, due to their excellent anti-fog and anti-bacterial performance [21]. The positive and negative charged groups can strongly and stably bind with water molecules through the electrostatically induced hydration interaction [22]. And, the high water content of zwitterionic polymer-grafted surface prevents organic foulants from irreversible adsorption and conformational change [23]. For this reason, Ezzat et al. modified the superhydrophilic poly(methacryloxyethyl sulfobetaine) polymer brushes with the surface-initiated atom transfer radical polymerization [24]. Among these preparation methods, some shortcomings are existed: 1) Some fabrication process is more expensive, complicated and environmental unfriendly. 2) The anti-fogging temperature range is narrow and the anti-fogging/anti-frosting performance is not effective under the boundary condition(extremely cold at $-40^{\\circ}\\mathrm{C}$ , military project, space and so on). 3) The superhydrophilic/hydrophilic coatings possess a number of hydrophilic functionalities such as hydroxyl (OH), amino $\\left(\\mathrm{NH}_{2}\\right)$ , carboxyl(COOH), ester(COOR), amide(NHCOR) and sulfonic $\\left(\\mathrm{HSO}_{3}\\right)$ . These hydrophilic functionalities are prone to interact with considerable water molecules, leading to the instability and dissolution of hydrophilic coatings, especially zwitterionic polymer. Inspired by the reported literature [20], the combination of hydrophobicity and hydrophilicity for the zwitterionic polymer would effectively maintain the balance between the water absorption and water penetration, beneficial for increasing the anti-fogging performance [25].  \n\n![](images/58844d7cc38cecc1ff856dda20713fe171b55a91185200cc3712782d224999e6.jpg)  \nScheme 1. Synthetic route for hydrophilic monomer (D-GMA).  \n\nIn this work, we have developed, for the first time, a facile and inexpensive method to obtain the dual-functional anti-fogging/antifrosting coatings with organic-inorganic zwitterionic polymer, featuring excellent anti-fogging performance under ultralow temperature even at $\\angle40^{\\circ}\\mathrm{C},$ less than the usage temperature of the previously reported literatures at $-20^{\\circ}\\mathrm{C}$ [26–28]. The self-designed silicone modified acrylic zwitterionic polymer is copolymerized by acrylic monomers as acrylic macromolecular skeleton, sulfonic acid quaternary ammonium salt as hydrophilic monomer and the silane as a stabilization component. These functional groups endow the silicone modified acrylic coating with the properties of low water contact angle, high transparency, good mechanical properties, long-term persistence [23] and excellent anti-fogging/anti-frosting performance. This result indicates that the silicone modified acrylic resin hydrophilic coating (SMA-H) is a novel and promising organic-inorganic zwitterionic anti-fog coating.",
        "category": " Introduction"
    },
    {
        "id": 5,
        "chunk": "# 2. Experimental",
        "category": " Materials and methods"
    },
    {
        "id": 6,
        "chunk": "# 2.1. Materials  \n\nDiethanolamine(DEA, $99\\ \\%$ ), N,N-dimethylformamide(DMF, 99.5 $\\%,)$ , butylacrylate(BA, 99 ${\\%},$ ), $^{2,2^{\\prime}}$ -azobis(2-methylpropionitrile) (AIBN,99 $\\left.\\begin{array}{c c c}{{0\\check{}}}&{{}}&{{}}\\\\ {{}}&{{}}&{{}}\\end{array}\\right.$ ), tetrahydrofuran (THF, $99~\\%$ ) and methyl methacrylate (MMA, $99\\ \\mathrm{~\\%~}$ ) were purchased from Aladdin. Glycidylmethacrylate (GMA, $99~\\%$ ), hydroxyethyl methacrylate(HEMA, $99~\\%$ ), 3-methacryloxypropyltrimethoxysilane(KH-570, 98 $\\%$ ) and ethylene glycol monomethylether (EE, $99\\ \\%$ ) were purchased from Adamas. 2-acrylamide-2-methylpropanesulfonic acid(AMPS,99 $\\left.\\begin{array}{r l}{\\centering}&{{}\\overline{{9/_{0}}}\\right|\\overline{{9/_{0}}}\\Biggr.$ ) and iso-propyl alcohol(IPO, $99.5~\\%$ ) was purchased from Sigma-Aldrich. All the chemicals were used as received.",
        "category": " Materials and methods"
    },
    {
        "id": 7,
        "chunk": "# 2.2. Synthesis of 3-(bis(hydroxymethyl)amino)-2-hydroxypropyl methacrylate (D-GMA)  \n\nFirstly, small hydrophilic molecules of 3-(bis(hydroxymethyl) amino)-2-hydroxypropyl methacrylate (D-GMA) was synthesized with diethanolamine (DEA) and glycidylmethacrylate(GMA) in the molar ratio of 1:1 in tetrahydrofuran solvent. DEA and GMA reactants were mixed and stirred for $^{3\\mathrm{h}}$ at $60^{\\circ}\\mathrm{C}$ under refluxing condition until the mixed solution was transparent. The aqueous supernatant fraction was remained after repeatedly washing with $5\\mathrm{\\sim}7\\mathrm{ml}$ dichloromethane and water to remove the unreacted DEA and GMA. The D-GMA was further acquired via rotary evaporation to remove the residual water in aqueous supernatant fraction with a yield of $30\\ \\%$ . The detailed synthesis procedure is shown in Scheme 1.",
        "category": " Materials and methods"
    },
    {
        "id": 8,
        "chunk": "# 2.3. Synthetic silicone modified acrylic resin (SMA-H)  \n\nNext, five monomers including the hydrophilic D-GMA/sulfonic acid quaternary ammonium salt(AMPS)/hydroxyethyl methacrylate (HEMA), the acrylic methyl methacrylate (MMA)/butyl acrylate (BA), the importantly hydrophilic silicone(KH-570) were copolymerized to obtain the silicone modified acrylic resin hydrophilic polymer(SMA-H). The synthesis of silicone modified acrylic resin (SMA-H) was divided into two steps. Firstly, $10\\mathrm{ml}$ DMF was heated to $60^{\\circ}\\mathrm{C}$ in the $250\\mathrm{ml}$ three-neck flask, followed by slowly adding MMA, BA and KH-570 in the molar ratio of 3:1:2 in turns. The AIBN concentration was approximately $0.3\\ \\%$ . After reaction for $^{\\textrm{1h}}$ , the low molecular weight copolymer was obtained. Secondly, the as-synthesized low molecular weight copolymer was subsequently reacted with the hydrophilic monomers, HEMA, AMPS and D-GMA (molar ratio: 3:1:3) at $60^{\\circ}\\mathrm{C}$ for $^{4\\mathrm{h}}$ . The synthetic route of the hydrophilic polymer (SMA-H) is displayed in the Scheme 2.",
        "category": " Materials and methods"
    },
    {
        "id": 9,
        "chunk": "# 2.4. Preparation and curing process of anti-fog coating  \n\nFirstly, the silicone modified acrylic resin hydrophilic polymer (SMA-H), the solvent, hydrolysis catalyst and the leveling agent were configurated to form the mixture of the silicone modified acrylic resin hydrophilic coating. The solvent was composed of iso-propyl alcohol (IPO) and ethylene glycol monomethylether (EE) in the volume ratio of 1:1. The silicone modified acrylic resin hydrophilic polymer and the solvent in the volume ratio of 2:3 were stirred to gain a diluted solution. Then, the diluted solution was reacted with the acetic acid solution $\\mathrm{(pH}=4$ , mass fraction $0.04\\mathrm{~\\}\\%$ ) and BYK-300 leveling agent (mass fraction $0.1\\%\\mathrm{~}$ at $40^{\\circ}\\mathrm{C}$ for $0.5\\mathrm{h}$ to give the mixture of silicone modified acrylic resin hydrophilic coating.  \n\nSecondly, the hydrophilic polymer of SMA-H was grafted onto the pretreated PC board, followed by curing. After washing and drying, the PC board in the size of $5\\mathrm{cm}\\times5\\mathrm{cm}$ was immersed into a solution including PVB(Polyvinyl butyral)and ethanol (the mass fraction of PVB was between $0.05\\substack{-0.1\\ \\%}$ ) for $3\\mathrm{min}$ . Then, the surface-treated PC board was taken out and dried at $80^{\\circ}\\mathrm{C}$ for $10\\mathrm{min}$ . The silicone modified acrylic hydrophilic coating with $\\sim20\\upmu\\mathrm{m}$ thickness was deposited onto the pretreated PC board by a bar applicator at the heat treatment temperature of $110^{\\circ}\\mathrm{C}$ for $^{2\\mathrm{h}}$ .  \n\n![](images/8a20de48a56de4824f150cf790a6845656b419d11216ff102a496f240453b76d.jpg)  \nScheme 2. Synthetic route for the hydrophilic polymer (SMA-H).",
        "category": " Materials and methods"
    },
    {
        "id": 10,
        "chunk": "# 2.5. Measurements  \n\nFTIR spectra were collected on an AVANAR360 FTIR spectrophotometer using potassium bromide (KBr) disk sampling technique. Differential Scanning Calorimetry (DSC) was conducted by a NETZSCH DSC404 F3 analyzer at a heating rate of $10^{\\circ}\\mathrm{C/min}$ in $\\Nu_{2}$ atmosphere. The thermal stabilities of the polymers were investigated by thermogravimetric analysis (TGA) on a METTLER TOLEDO TGA/1600 L F thermo gravimetric analyzer in $\\Nu_{2}$ atmosphere with the heating rate of $10\\mathrm{^{\\circ}C/m i n}$ from room temperature to $600^{\\circ}\\mathrm{C}$ . X-ray photoelectron spectroscopy (XPS, Kratos Axis Ultra DLD) was monitored with Al Ka probe beam to analyze the chemical composition of the anti-fog coating. Atomic force microscopic (AFM) images were tested with Asylum Research Probe MFP-3D-BIO microscope to capture the surface morphology of the coating. The water contact angle was measured by XYCXIE XG-CAMB2-X water contact meter. The thickness of the coating was measured by the DualScope MP0R thickness gauge (Germany, Fisher). In addition, the adhesion of coating was evaluated according to Chinese National Standard GB/T9286-88 or ISO 2409 Standard [1].",
        "category": " Materials and methods"
    },
    {
        "id": 11,
        "chunk": "# 2.6. Anti-fog and anti-frost tests  \n\nHigh-temperature anti-fog experiment was carried out by placing the samples above the beaker mouth filled with hot water $(80^{\\circ}\\mathrm{C})$ for 10 s (The distance between the sample and the water surface is $5\\mathrm{cm}$ ). In low temperature anti-fog/frost test, the samples were also put into a refrigerator at certain temperature for $30\\mathrm{min}$ , followed by taking out of refrigerator to ambient condition $20^{\\circ}\\mathrm{C}$ , $50\\%$ relative humidity) for 5 s and recording the surface morphology on PC board. To quantitatively evaluate the transparency of the as-prepared anti-fogging/anti-frosting coating, the light transmission measurement was immediately conducted after these samples were exposed to fogging/frosting environment by the 721 UV–Vis spectroscopy in the wavelength range of $380-780\\mathrm{nm}$ .",
        "category": " Materials and methods"
    },
    {
        "id": 12,
        "chunk": "# 3. Results and discussion",
        "category": " Results and discussion"
    },
    {
        "id": 13,
        "chunk": "# 3.1. Chemical composition  \n\nFig. 1(a) and (b) show the FTIR spectra of the hydrophilic monomer D-GMA and the hydrophilic polymer (SMA-H), respectively. As shown in Fig. 1(a), the IR spectrum of the reactant GMA has obviously characteristic absorption peaks at $850\\mathrm{cm}^{-1}$ and $910\\mathrm{cm}^{-1}$ , corresponding to the symmetric ring deformation and the symmetrical stretching vibration of epoxy function group, respectively [29]. In contrast, the absorption peaks at $850\\mathrm{cm}^{-1}$ and $910\\mathrm{cm}^{-1}$ disappear in the IR of DGMA, which indicates that the epoxy groups participate in the ring opening reaction. As for D-GMA, an distinct stretching vibration absorption peak at $1640\\mathrm{cm}^{-1}$ for $\\mathsf C=\\mathsf C$ [30] represents the successful preparation of the monomer D-GMA in Fig. 1(a). The IR spectrum of the silicone modified acrylic resin is also presented in Fig. 1(b). As can be seen in Fig. 1(b), the peak intensity at $1640\\mathrm{cm}^{-1}$ of SMA-H associated with the $\\mathsf{C}{=}\\mathsf{C}$ group is very weaker than that of GMA, demonstrating the successful copolymerization of all the monomers. As for SMA-H, the stretching vibration absorption bands at $1197\\mathrm{cm}^{-1}$ [31] and $1043\\mathrm{cm}^{-1}$ [32] are assigned to the organic sulfonate in Fig. 1(b). The absorption peak of the hydroxyl group at stretching vibration $3500\\mathrm{cm}^{-1}$ is also observed in the FTIR spectrum of the product SMA-H, as seen in Fig. 1(b). These hydrophilic groups comprising of the hydroxyl and the zwitterionic salt efficiently contribute to the increasing of the anti-fog/anti-frost properties for the silicone modified acrylic resin hydrophilic anti-fog coating. As expected in Scheme 2, the structure of SMA-H is further confirmed by the presence of carbonyl stretching vibration absorption peak at $1720\\mathrm{cm}^{-1}$ [32].",
        "category": " Results and discussion"
    },
    {
        "id": 14,
        "chunk": "# 3.2. Glass transition temperature  \n\nThe glass transition temperature characterizes the transition temperature of amorphous polymers from glassy to high elasticity. Fig. 2(a) displays the DSC curve of hydrophilic anti-fogging coating. From Fig. 2(a), the glass transition temperatures(Tg) of the anti-fogging coating is approximately $65^{\\circ}\\mathrm{C}$ . It means that the coating exhibits elasticity when the temperature is above $65^{\\circ}\\mathrm{C}_{\\mathrm{i}}$ while the hydrophilic anti-fogging coating shows the property of brittleness when the temperature is lower than $65^{\\circ}\\mathrm{C}$ . Thus, the operating temperature of hydrophilic anti-fogging coating should be controlled below $65^{\\circ}\\mathrm{C}$  \n\nFig. 2(b) gives the DTA-TGA curves of the silicone modified acrylic resin hydrophilic anti-fog coating. It can be apparently seen in Fig. 2(b) that the hydrophilic coating is very stable after curing when the temperature declines to $360^{\\circ}\\mathrm{C}$ . When the temperature is below $200^{\\circ}\\mathrm{C}$ , no significant mass loss implies the absence of solvent in the coating after curing at $110^{\\circ}\\mathrm{C}$ . This result shows the excellent heat stability of the hydrophilic coating. From DTA curve in Fig. 2(b), a strong endothermic peak at $\\sim65^{\\circ}\\mathrm{C}$ is attributed to the glass transition temperature and the other endothermic peak at $360^{\\circ}\\mathrm{C}$ represents the disintegration of silicone modified acrylic resin coating, similar to the previous report [33].",
        "category": " Results and discussion"
    },
    {
        "id": 15,
        "chunk": "# 3.3. Anti-Fog properties  \n\nIn this work, the anti-fogging tests of the coating were evaluated at low temperature $(-20^{\\circ}\\mathrm{C},\\ -40^{\\circ}\\mathrm{C})$ and high temperature $(80^{\\circ}\\mathrm{C})$ . In high temperature anti-fog test, a SMA-H-coated PC board and the bare board were put on a cup of hot water $(80^{\\circ}\\mathrm{C})$ . In low temperature antifog test, the samples were put into a refrigerator for $30\\mathrm{min}$ and the surface appearance was recorded 5 s after removal to ambient temperature $20^{\\circ}\\mathrm{C}$ , $50\\%$ relative humidity).  \n\nFig. 3 shows the anti-fog test results of the surface-treated and the bare PC board at different temperatures. As for the bare PC board, the fogging phenomenon is immediately observed on the surface of the bare PC boards at low temperature $(-20,\\ -40^{\\circ}\\mathrm{C})$ and high temperature $(80^{\\circ}\\mathrm{C})$ in Fig. 3(a–c). It can be clearly observed in Fig. 3(a), a large amount of water droplets on the bare PC board blurs our vision and diminishes the transparency of the PC board. Nevertheless, the PC boards treated with silicone modified acrylic resin hydrophilic coating still retain a good transparency at −20, −40 and $80^{\\circ}\\mathrm{C}$ in Fig. 3(a–c). The school badge of Chongqing University is clearly visible through the PC boards covered with SMA-H coating. In comparison with the previous literatures [19,24–27,30,31], the as-prepared coating exhibits an excellent anti-fog performance at low temperature $-40^{\\circ}\\mathrm{C}$ . It is mainly due to successful reduction of the freezing point of the water by the quaternary ammonium salt groups in the polymer. The anti-fog results testify that the anti-fog coatings have good optical transparency with wider temperature range of applications.  \n\n![](images/16421f46cbeebf891119602c721eb828704a5a0da31e7d3621c067ab91c6bc16.jpg)  \nFig. 1. FTIR spectra of hydrophilic monomer (D-GMA) (a) and hydrophilic polymer (SMA-H) (b).",
        "category": " Results and discussion"
    },
    {
        "id": 16,
        "chunk": "# 3.4. Transparency  \n\nFig. 4(a) and (b) display the transmittance of the coated and bare PC board before and after fogging $(-40^{\\circ}\\mathrm{C})$ , respectively. As can be seen in Fig. 4a, the transmittance of the coated PC is slightly higher than that of the bare PC in the range of $380-780\\mathrm{nm}$ (91 vs. $89\\%$ ) before the antifog test. After the anti-fog test at $\\angle40^{\\circ}\\mathrm{C},$ the transmittance of the bare sample is decreased to $21\\ \\%$ owing to the surface fog formation, whereas the surface-treated PC board still shows high transmittance of $91\\%$ in Fig. 4(b), indicating an excellent anti-fog property of the asprepared hydrophilic coating. The main reason for this is that a certain amount of water molecules could interact with the hydrophilic coating as non-freezable bond water through hydrogen bonds and spread uniformly on the PC surface [34].",
        "category": " Results and discussion"
    },
    {
        "id": 17,
        "chunk": "# 3.5. Stability and adhesion  \n\nFig. 5 shows the stability test result of the as-prepared coating after multiple anti-fog tests at $-40^{\\circ}\\mathrm{C}$ . After every anti-fog test, the PC surface is slightly wiped and dried. It can be clearly seen from Fig. 5(a–c) that the as-prepared coating on PC board still shows a good anti-fog feature even after 100 times of anti-fog tests. After repeated tests, the coating still remains good anti-fog performance without scaling, dropping and cracking phenomenon. As also can be observed, the silicone modified acrylic resin hydrophilic coating is still transparent on the whole and has outstanding stability after 100 times of anti-fog tests. Additionally, the adhesion of the coating was measured after 100 times of anti-fog tests at $-40^{\\circ}\\mathrm{C}$ , according to Chinese Standard GB/T9286-88 of the cross-cut method. Fig. 5(d) shows the adhesion test result of the as-prepared coating after 100 times of anti-fog tests. As shown in Fig. 5(d), the coating maintains the intact surface and exhibits the best level of ISO 0 grade according to Chinese national standard GB/T9286- 88, indicating the high durability of the coating on the PC substrate in a certain extent. The pencil hardness of the as-prepared multiple anti-fog coating can reach up to 3H, higher than those of the conventional coatings on the market, such as UV coating(2 H), Epoxy primer(1 H) and so on. The good mechanical property of the as-prepared coating is attributed to the compromise between the Si-O-Si bond and hydrophilic functionalities, specially zwitterionic group. In brief, the silicone modified acrylic resin hydrophilic coating ensures the reliability and durability in consideration of color, transparency and adhesion performance.  \n\n![](images/bcef4b5d8c2c3f6285658499ff56424c6026152217383622c7722787002f5c7c.jpg)  \nFig. 2. (a) DSC curve of hydrophilic anti-fog coating; (b) DTA-TGA curves of the anti-fog coating heated from room temperature to $600^{\\circ}\\mathrm{C}$ at a heating rate of $10^{\\circ}\\mathrm{C}$ $/\\mathrm{min}$ in $\\mathbf{N}_{2}$ atmosphere.  \n\n![](images/9f3dd02e10e086ce8c9f5f3335ab3e924aa5ce3a37b2f2cac94990900234cb6d.jpg)  \nig. 3. Anti-fog test of the bare samples and surface-coated samples at (a) $-20^{\\circ}\\mathrm{C};$ $(\\boldsymbol{\\mathbf{b}})-40{}^{\\circ}\\boldsymbol{\\mathbf{C}};$ (c)",
        "category": " Results and discussion"
    },
    {
        "id": 18,
        "chunk": "# 3.6. Analysis of the surface  \n\nThe excellent anti-fog/anti-frost performance and good stability of the cured SAM-H coating on PC board is expounded by means of X-ray photoelectron spectroscopy. Fig. 6(a) shows the XPS survey spectrum of the cured SAM-H coating. As expected, the cured SAM-H coating consists of C, N, O, S and Si elements in Fig. 6(a). Fig. 6(b)–(e) displays the high-resolution spectra of C1s, O1s, N1s, Si2p, respectively. As can be shown in Fig. 6(b), the C1s peak originates from the CeO (285.91 eV), $\\mathsf{C}{\\mathrm{-}}\\mathsf{H}$ $284.42\\mathrm{eV})$ , $\\scriptstyle{\\mathsf{C}}=0$ (288.47 eV), CeN $285.6\\mathsf{e V}$ [35] and C-Si $(283.4\\mathrm{eV})$ [36]. The O1s spectrum in Fig. 6(c) is composed of four peaks, which are located at $531.09\\mathrm{eV}$ , 531.53 eV, $531.83\\mathrm{eV}$ and $532.97\\mathrm{eV}$ . The O1s peak at 531.09 eV can be ascribed to the $_{\\mathsf{C}-\\mathsf{O}}$ bond according to the XPS handbook and the other three O1s peaks are attributed to $\\scriptstyle\\mathtt{C=}0$ (531.53 eV) [37], Si-O(531.83 eV) [38] and Si-O-Si (532.97 eV) [39], respectively. In Fig. 6(d), the N1s peak can be fitted with three individual peaks at $399.09\\mathrm{eV}$ , 401.1 eV and 401.86. eV, corresponding to the N- $(\\mathrm{CH}_{3})_{3}$ group of the reactant (AMPS), the $\\boldsymbol{\\mathrm{N-H}}$ and the ${{\\bf{C}}{\\bf{-}}{\\bf{N}}^{+}}$ group of the hydrophilic polymer(D-GMA) [37], respectively. As for $\\mathtt{s i2p}$ spectrum in Fig. 6(e), the Si2p peak situated at $102.14\\mathrm{eV}$ and $101.46\\mathrm{eV}$ can be assigned to two components of the $S\\mathrm{i}-\\mathsf{C O}_{3}$ [40] and Si- $(\\mathsf{C}_{2}\\mathsf{O}_{2})$ groups [39], respectively. These findings verify that the macromolecular network structure of the cured SMA-H coating on PC board is formed by the co-condensation reaction between the $S\\mathrm{i}{-}0\\mathrm{H}$ bonds of the anti-fog coating and the $_{\\mathrm{O-H}}$ bonds of the pretreated surface of PC board, whose the highly crosslinked backbone is Si-O-Si siloxane bonds. Fig.7 shows the schematic illustration of the SMA-H coating formed on the PC substrate, elucidating the mechanism of the chemical interaction between the SMA-H coating and the PC board. This illustration gives a good explanation to the enhanced stability of hydrophilic SMA-H coating by implementing the perfect compromise between the hydrophobicity and hydrophilicity.  \n\n![](images/dbb64c115e3b489ce05b3cea3ec40e0ca82c00900a97987106b3bf3d764a9044.jpg)  \nFig. 4. UV–vis spectra of the surface-coated and bare PC board (a) before and (b) after fogging $(-40^{\\circ}\\mathrm{C})$  \n\n![](images/aac7df4ecee316b5ee21c1f3c8075f3c97471e158632587365e9c87f4014dbce.jpg)  \nFig. 5. Stability test of the coating after multiple anti-fog tests: (a) 20 times; (b) 50 times; (c) 100 times.  \n\n![](images/3b9e4b7ac51d0ca38325d0c4655407cbdda1e7762f9d7462127b60804fca8de4.jpg)  \nFig. 6. XPS spectra of the cured SMA-H coating (a) Survey; (b) C1s; (c) O1s; (d) N1s and (e) Si2p.  \n\n![](images/a4d591269299f768dea32914fff324efe948fa053142fc009fc75b84134c94de.jpg)  \nFig. 7. Schematic illustration of the SMA-H coating formed on the PC substrate.  \n\n![](images/d667db37be53f1d789c4947c87ae673be6cad4c893f39d5fd7e4b52f84bfc560.jpg)  \nFig. 8. AFM topography (left) and phase (right) images of the cured anti-fog coating on PC board.  \n\n![](images/3c286c1a580bbfda458cad1898cdf9addc86ce6abe78a2626703bd4b9fbad494.jpg)  \nFig. 9. The water contact angle profile of the bare sample (a) and the coated sample (b).  \n\nAtomic force microscopy (AFM) was adopted to detect the physical properties and micromorphology of material in order to further clarify the anti-fog mechanism of the zwitterionic hydrophilic polymer. The topography (left) and phase (right) images of the cured SMA-H coating surface are given in Fig. 8 with tapping-mode AFM in air under ambient conditions. The high Rq roughness of the SMA-H coating from the topography images in Fig. 8(a, c) is $\\sim3.574\\mathrm{nm}$ , suggesting the porous/ rough properties of the SMA-H coating surface decreasing its optical reflection [41]. Fig. 8(b) and (d) show the phase images of SMA-H coating. In a typical AFM phase image of a micro-phase separated polyurethane, the lighter regions represent the hard phase, whereas the darker regions assign the soft phase [42]. In the light of the lighter and darker image, we can easily distinguish the hydrophilic (the soft) region from the hydrophobic (the hard) region on the surface of SMA-H coating. The yellow soft region in Fig. 8(b, d) is continuously distributed on the surface of SMA-H coating. The growing-condensed water droplets gradually adsorb and spread onto large areas of the hydrophilic region, accompanied by their decreased surface tension [20]. In Fig. 8(d), the area of the hydrophobic domains is only less than $100\\mathrm{nm}^{2}$ and the hydrophobic area is fully surrounded by the hydrophilic materials, which further explains why the coating has an outstanding anti-fogging performance.",
        "category": " Results and discussion"
    },
    {
        "id": 19,
        "chunk": "# 3.7. Assessment of the wetting behavior  \n\nTo further elaborate the anti-fog/anti-frost mechanism, the water contact angle was measured to evaluate the anti-fog performance in term of the wettability of coating surface. Fig. 9(a, b) show the water contact angle profiles of the bare sample and the coated sample, respectively. As can be displayed in Fig. 9(a) and (b), the water contact angles of the bare and surface-treated PC boards are $78^{\\circ}$ and ${\\sim}10^{\\circ}$ respectively. It is widely accepted that the solid surface is hydrophilic when the water contact angle is less than $90^{\\circ}$ , whereas the solid surface is hydrophobic when the water contact angle is greater than $90^{\\circ}$ [43]. The smaller the contact angle, the better the liquid's wettability of the solid. Wettability can characterize the degree of affinity between a liquid and a solid surface and the contact angle is the important parameter that quantifies the wettability. Upon balancing the interface tensions between the solid/vapor, solid/liquid, and liquid/vapor interface, water drops tend to minimize the total surface free energy while maintaining its volume [44]. The shape of liquid drops is typically spherical on the hydrophobic surface. Hence, the water drops on the bare PC board in Fig. 9(a) resembles sphere, which is very similar to the morphology of the hydrophobic surface [44]. In contrast, the water contact angle of the surface-coated sample is very small $(10^{\\circ})$ . The main reason for this is that the liquid drops spread over the hydrophilic surface to form a sheet-like layers in Fig. 9(b) with the synergistic effect of the $-\\mathrm{OH}$ groups and the zwitterionic of the SMA-H coating. As a result, the coated surface of the PC board remains optical transmittance even after the anti-fogging test under ultralow temperature at the $\\angle40^{\\circ}\\mathrm{C}$ . Simultaneously, the Si-O-Si groups provide a water-fast mesh structure and prevents the SMA-H coating from being dissolved in water.",
        "category": " Results and discussion"
    },
    {
        "id": 20,
        "chunk": "# 4. Conclusion  \n\nIn this article, we fabricated a novel effective organic-inorganic zwitterionic acrylate anti-fog/frost coating via free radical copolymerization. The organic-inorganic zwitterionic acrylate coating consists of the hydroxyl groups, the sulfonic acid quaternary ammonium salt and silicon oxygen network structure confirmed by IR and XPS. The unique structure endows the polymer coated on polycarbonate (PC) substrate with excellent anti-fog performance and good stability (repeated use for 100 times) under wider temperature range $(-40\\sim80^{\\circ}\\mathrm{C})$ of applications. The glass transition temperatures(Tg) of the anti-fogging coating is about $65^{\\circ}\\mathrm{C}$ . After anti-fogging test under ultralow temperature at $\\angle40^{\\circ}\\mathrm{C},$ the light transmittance value of the grafted-coating on PC board still maintain $91\\%$ , significantly better than that of the bare PC board $21\\ \\%$ . AFM images demonstrate that the hydrophilic (the soft) region is continuously distributed on the surface of SMA-H coating. As for the coated PC board, the smaller water contact angle of $10^{\\circ}$ indicates better hydrophilicity and wettability. The as-prepared organic-inorganic zwitterionic acrylate anti-fog/frost coating will promote the extensive application of transparent polycarbonate (PC) material with a facile and low-cost preparation route.",
        "category": " Conclusions"
    },
    {
        "id": 21,
        "chunk": "# CRediT authorship contribution statement  \n\nZiyang Zheng: Investigation, Conceptualization, Methodology, Software, Data curation, Formal analysis, Writing - original draft. Yuping Liu: Funding acquisition, Investigation, Methodology, Formal analysis, Software, Writing - review & editing. Li Wang: Funding acquisition, Formal analysis, Visualization. Li Yu: Investigation, Data curation, Formal analysis. Yuan Cen: Software, Formal analysis, Validation. Tingting Zhu: Investigation, Formal analysis, Software. Danmei Yu: Resources, Supervision, Validation. Changguo Chen:  \n\nProject administration, Methodology, Supervision.",
        "category": " Abstract"
    },
    {
        "id": 22,
        "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": " Conclusions"
    },
    {
        "id": 23,
        "chunk": "# Acknowledgments  \n\nThis research was supported by the National Natural Science Foundation of China under Grant No. 21406021.",
        "category": " References"
    },
    {
        "id": 24,
        "chunk": "# Appendix A. Supplementary data  \n\nSupplementary material related to this article can be found, in the online version, at doi:https://doi.org/10.1016/j.porgcoat.2020. 105578.",
        "category": " References"
    },
    {
        "id": 25,
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    }
]