A novel organic-inorganic zwitterionic acrylate polymer for high-performance anti-fog coating
Graphical abstract
Introduction
Polycarbonate (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°<θ<10° and 10°<θ<40-50°, respectively. Then, developing a stable hydrophilic coating with versatile functionalities and facile process is essential for its practical application in hydrophilic anti-fog coating.
More 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 °C, military project, space and so on). 3) The superhydrophilic/hydrophilic coatings possess a number of hydrophilic functionalities such as hydroxyl (OH), amino(NH2), carboxyl(COOH), ester(COOR), amide(NHCOR) and sulfonic(HSO3). 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].
In this work, we have developed, for the first time, a facile and inexpensive method to obtain the dual-functional anti-fogging/anti-frosting coatings with organic-inorganic zwitterionic polymer, featuring excellent anti-fogging performance under ultralow temperature even at −40 °C, less than the usage temperature of the previously reported literatures at −20 °C [[26], [27], [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.
Section snippets
Materials
Diethanolamine(DEA, 99 %), N,N-dimethylformamide(DMF, 99.5 %,), butylacrylate(BA, 99 %,), 2,2′-azobis(2-methylpropionitrile)(AIBN,99 %), tetrahydrofuran (THF, 99 %) and methyl methacrylate(MMA, 99 %) 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 %) and iso-propyl
Chemical composition
Fig. 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 cm−1 and 910 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 cm−1 and 910 cm−1 disappear in the IR of D-GMA, which indicates that
Conclusion
In 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)
CRediT authorship contribution statement
Ziyang 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,
Declaration of Competing Interest
The 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.
Acknowledgments
This research was supported by the National Natural Science Foundation of China under Grant No. 21406021.
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