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Silica and Silane based polymer composite coating on glass slide by dip-Coating Method
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Silica and Silane based Polymer Composite Coating on Glass slide by Dip-coating Method Sangeetha Sriram , R.K. Singh , Aditya Kumar PII: DOI: Reference:
S2468-0230(19)30673-X https://doi.org/10.1016/j.surfin.2020.100472 SURFIN 100472
To appear in:
Surfaces and Interfaces
Received date: Revised date: Accepted date:
19 November 2019 4 February 2020 8 February 2020
Please cite this article as: Sangeetha Sriram , R.K. Singh , Aditya Kumar , Silica and Silane based Polymer Composite Coating on Glass slide by Dip-coating Method, Surfaces and Interfaces (2020), doi: https://doi.org/10.1016/j.surfin.2020.100472
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Highlights
The superhydrophobic coating on glass synthesized silica and silane-based polymer composite coating (SiNps, PFOTS, and PMMA)by dip-coating method
Examined surface morphologies, contact angles, and chemical compositions of coatings.
Coatings are thermal, chemical, mechanical, and UV stable.
Superhydrophobic glass exhibits the excellent self-cleaning property and 91% transparency
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Silica and Silane based Polymer Composite Coating on Glass slide by Dipcoating Method Sangeetha Sriram1*, R.K. Singh1, and Aditya Kumar2 1
Department of Chemical Engineering, National Institute of Technology Rourkela 769008,
Odisha, India 2
Department of Chemical Engineering, Indian Institute of Technology (ISM) Dhanbad,
826004, Jharkhand, India Abstract
Superhydrophobic coatings are widely used for various engineering applications, namely, self-cleaning and self-healing for engineering structures. Therefore, in recent decades, a number of industries have shown significant interest in the development of superhydrophobic coatings for various purposes. In view of the above demands, this study presents explicitly a cost-effective and facile method to fabricate superhydrophobic transparent coating on the glass. The superhydrophobic coating was prepared by dip-coating technique with sol-gel of polymethyl methacrylate-co-ethyl acrylate
polymer
(PMMA),
SiO2nanoparticles
(SiNps)
and
1H,
1H,
2H,
2H
perfluorooctyltrichlorosilane (PFOTS). Wettability, surface morphology, and the transparency of coating were investigated. Also, the stability of the coating was assessed at harsh conditions like annealing at high temperatures (40-400 °C), irradiation by UV light, and pH resistance at different alkali and acidic conditions (2-13), and mechanical durability by performing water-jet, abrasion and adhesion tests were studied. The coated glass exhibits a static water contact angle (CA) of 174 ± 2° and with a sliding angle (SA) of 4 ± 1°. Furthermore, the coating exhibits excellent self-cleaning property, and more than 91% of the transparency of the coating was assessed. All the results indicated that such type of coatings could also use for self-cleaning and transparent coatings at the industrial level.
Keywords: Superhydrophobicity; Silica and silane-based polymer coating; Stability & durability; Self-cleaning &Transparency;
*Corresponding author: [email protected](Sangeetha. Sriram)
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1. Introduction
Superhydrophobic surfaces are well defined as substrates that have apparent advancing or receding contact angle greater than 150° and roll-off angle lower than 10°. For past decade researchers from the academics, industrial scientists, and engineers are showing much more attention to the synthesis of superhydrophobic surfaces motivated by natural surfaces like a lotus leaf, insect legs, butterfly wings, animal fur, feathers [1-4]. There are many techniques available to fabricate the artificial superhydrophobic coatings such as dipcoating [5], etching [6], sol-gel technique [7], chemical vapor deposition [8, 9], solution immersion [10], spray coating[11], spin coating [12]. These surfaces are providing potential applications such as anti-fogging [13], self-cleaning [14, 15], anti-fouling [16], anti-corrosion [17], anti-bacterial [18], anti-icing [7], drag reduction [19], anti-reflective [20], and oil-water separations [21, 22].
Glass surfaces are using in various applications in day to day life. glass is the use of most common optical material for lenses, windshields, architectural windows, solar panels, eye-catching interior, exterior walls, and glass ceilings. Based on regular usage, these surfaces need cleaning and maintenance. This requires a transparent and dust-free protective superhydrophobic layer to reduce the cost, effort, and time. Many researchers have been reported the transparent coatings on glass substrates. For example, Ebert et al. fabricated transparent, superhydrophobic, and wear-resistant coatings on glass and plastic substrates with the use of different nanoparticles such as SiO2, ZnO, and ITO [23]. Wang et al. reported a transparent and anti-fingerprint superhydrophobic thin film using polyaniline nanofibers on steel with fluoro-thiol modification [24]. Yokoi et al. reported optically transparent superhydrophobic polyester mesh surface with enhanced mechanical abrasion resistance by
3
using a three-step process using perfluorooctyltrichlorosilane, perfluorodecyltrichlorosilane, and NaOH[25].
Recently, Li et al. described a one-step process to fabricate superhydrophobic coating with high transparency with the use of trimethoxypropylsilane and fumed silica nanoparticles on the glass surface [26]. Latthe et al. developed the superhydrophobic and self-cleaning coatings on glass substrate using silica-PMMA composite with methyltrimethoxysilane compound by sol-gel process technique [27]. Xu et al. fabricated raspberry-like SiO2 nanoparticles/ polystyrene by adding methacryloxypropyltrimethoxysilane to mini-emulsion polymerization of styrene [28]. Nanda et al. synthesized functionalized silica microparticles for self-cleaning applications on glass substrates with octadecyl trichlorosilane by employing the sol-gel method [29]. Chang et al. fabricated superhydrophobic films via deposition of raspberry-like fluorescent PS/CdTe/silica microspheres on glass substrates [30]. Guo et al. fabricated light-diffusing films for LED applications by strawberry-like PMMA/SiO2 composite microspheres [31].
The superhydrophobic coatings on glass substrates were created by Bravo et al. with the use of cationic solutions of poly (allylamine hydrochloride) and anionic solutions of silica nanoparticles and trichloroperfluorooctyl silane via chemical vapor deposition [32]. Xu et al. fabricated anti-reflective and superhydrophobic coatings on glass substrates with the use of hydrophobic hexamethyldisilazane and perfluorooctyltriethoxysilane modified hollow silica nanoparticles and PMMA via dip-coating method [33]. Li et al. synthesized the superhydrophobicity on glass substrates via layer-by-layer assembly, followed by the calcination
process
with
the
use
of
mesoporous
silica
nanoparticles,
perfluorooctyltriethoxysilane, and poly diallyldimethylammonium chloride [34]. Xu et al. fabricated superhydrophobic thin films on glass substrates with the use of different materials
4
like SiO2 nanoparticles and perfluorooctyltrichlorosilane (PFOTS) [20]. Suwan et al. synthesized the superhydrophobic films on glass substrates by employing dip-coating and spray-on coating techniques with the use of PMMA/SiO2 nanocomposite and PTOS silane compound [35]. Bayer has articulated in his review paper, that in order to reveal liquid repelling coatings with durability and wear resistance is a significant factor, where the surfaces will provide the technical and large scale applications, and reported different types of durability and wear resistance of the transparent superhydrophobic coatings [36].
The current work focuses on the development of silica and silane-based polymer composite coating (SiNps, PFOTS, and PMMA) on glass by a simple dip-coating method. Coating shows stable superhydrophobic nature under extreme conditions of elevated temperatures, acid and alkali environment, UV light irradiation, and mechanical disturbances. Self-cleaning and transparency of coating have also examined.
2. Materials and methods
2.1. Materials
PMMA (average Mn ~39,500 and average Mw ~101,000), SiO2 nanoparticles (1020 nm), and 1H, 1H, 2H, 2H perfluorooctyltrichlorosilane (PFOTS – silane coupler) (≥ 97% purity) were purchased from Sigma-Aldrich Co., USA. Microscopic glass slides (76 mm X 26 mm X 1.25 mm) were obtained from Borosil Glass Works Ltd., India. Toluene and propanol were procured from Merck Specialties, Private Limited, India. Millipore water (18.2 mΩ cm resistivity) was used. Before developing the coating, all the substrates were washed with the tap water first, and removing the impurities on the substrates were then washed by Millipore water in ultra-sonicator for 15 min. Later on, the substrates again washed with isopropanol and were cured in an oven for overnight at 40°C.
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2.2 Coating procedure
Fig. 1. is representing the schematic illustration of superhydrophobic coating on the glass slide. The silica and silane-based polymer composite coating solution were prepared by adding PMMA(2 %, wt/v) and SiNps(1 %, wt/v) in 40 ml of toluene and stirred at 45 °C for 25 min. To this mixture, PFOTS silane coupler (1%, v/v) was then added and further continued the stirring for 15 min. To get the uniform dispersion of sol-gel was further sonicated for 20 min by using ultrasonicator. The solution was then dip-coated on the glass surface, which was later dried in a hot air oven for 5 h at a temperature of 60 °C.
2.3 Characterizations
The static water contact angle (CA) of the samples at room temperature was measured with the Drop Shape Analyzer (DSA 25 Krüss GmbH, Hamburg, Germany). The surface morphologies of the specimens observed using scanning electron microscopy (SEM, Nova Nano SEM FEI, Hillsboro, Oregon, USA). The elemental analysis of the samples was done by energy dispersive X-ray spectroscopy (EDX, Nova Nano SEM FEI, Hillsboro, Oregon, USA). The surface roughness and thickness of the film (ASH- average step height) were evaluated by using a stylus profilometer instrument (Veesco Dektak 150) with Dektak 150 software. 4-7 µl volume range of single water droplet was used for measurements of CA. CA measurements were repeated at five different locations of each sample, and the average of CA was reported in this work. Functionalization of SiNps-PFOTS-PMMA analyzed by FTIR (Thermo Fisher Nicolet iS10) instrument. The transparency of the coated and bare glass was measured by a UV-Vis spectrophotometer (Jasco V-750 UV- visible spectrophotometer). 6
3. Results and discussion
3.1. Morphology and wettability
Cleaned uncoated silicon glass slide surface shows a water static contact angle of 32 ± 3°, and it’s in hydrophilic. After coating with silica and silane-based polymer composite coating, the static water contact angle of the coated sample is increased to 174 ± 2° and sliding angle 4 ± 1°, uncoated and coated samples surface morphologies were also studied by
SEM, images as shown in Fig. 2. The coated glass surface exhibits rough islands like morphology in the microstructure, while at higher magnification SEM photographs reveal clustered non-spherical rough nano/microstructures along with pores present on the surface, and these microstructures provide the roughness to the surface. The resulting nano-micro hierarchical roughness on the coated glass surface is enhancing the superhydrophobicity. Whereas the uncoated glass shows the plain surface without rough structures. Xu et al. reported similar surface morphology of micro/nanoscale hierarchical roughness for superhydrophobic coating on the glass, which was produced by using SiO2 nanoparticles, TEOS, and PFOTS [20]. The roughness and film thickness of the coated glass surface and uncoated glass using a stylus profilometer. The roughness is measured 6.2 ± 0.6 µm, and 2.9 ± 0.7 µm for coated and uncoated glass surface respectively. Film thickness was calculated by the average step height (ASH), and it is 6.60 ± 0.30 µm.
Further, EDX of both uncoated and uncoated glass was carried out, as shown in Fig. 2, and it confirms the presence of carbon, oxygen, silicon, fluorine, and chlorine on the coated glass, and oxygen, silicon, sodium, magnesium, and calcium on the uncoated glass 7
surface. The functionalization of SiNps-PFOTS-PMMA coating was also confirmed via IR spectra, as shown in Fig. 3 (coated peak).A peak at 2954 cm−1 corresponds to C-H stretching [37]. Peaks from 1450 to 700 cm−1are validated to the various C=H and C=F bonds of PFOTS [38]. The peak at 1735.23 cm−1 represents the C = O stretching. The peak at 1384.64 cm−1 shows the C-H asymmetric stretching of PMMA[39]. The frequency at 1098.74 cm−1and 807.74 cm−1 and 466.30 cm−1Si -O - SH stretching and Si-O-Si bending vibrations, respectively [40]. FTIR and EDX confirm the existence of low surface energy materials of PMMA, PFOTS, and SiNps on the coated glass. Through the optimal mixture of low surface energy material and roughness, coating shows the superhydrophobic nature.
3.2. Wetting stability of the coatings
For industrial and practical applications, superhydrophobic surfaces should last under extreme surroundings. So, the stability and durability of these surfaces were widely and systematically inspected under a sequence of extremely harsh conditions.
An approach of the annealing experiment was carried out using the method reported earlier [22]. The assessment of annealing was examined by exposing the coated glass samples to elevated temperatures. The coated samples were pre and post annealed for 1 h at different temperatures (40 to 400 °C). The CA was measured after cooling the samples. Fig.4 (a) indicates the water CA values against all annealing temperatures. It also shows the morphology of the uncoated and coated sample before and after annealing at 400 °C Fig. 4 (b). The CA 173° ± 1° and sliding angle of 3.2° ± 0.5° were unchanged up to an annealing temperature of 380 °C, and water droplet rolls from the surface. While at 400 °C, the sample loses its superhydrophobic nature, and it turns into hydrophobic as water contact angle reduced to 95.4°± 7° and sliding angle greater than 20°. And due to the sample surface degradation, and cracks were formed on the surface. EDS analysis was performed to observe 8
any change in the composition before and after annealing, from the EDS graph (fig 4(c)) data it has been noticed that chlorine percentage has declined in annealed condition than compared to the non-annealed condition. This could be due to desorption during annealing [20].
To examine the pH stability of the superhydrophobic coating was evaluated after immersing the samples in acid and alkali solutions of various pH (2, 5, 8, 11, and 13), as reported previously [29]. CA of samples at various pH after 400 h of dipping is shown in Fig.5. The wetting property of samples retained even after 400 h of immersion in the acid and alkali solutions, displaying the outstanding pH stability of the coating. The contact and sliding angles were measured and reported as 171.9° and <5 ± 0.6°, 171.2° and <5 ± 0.2°, 171.1° and <4 ± 0.5°, 171.0° and 4.2 ± 0.5°, and 169.3°and <4.8 ± 0.5°, for various pH 2, 5, 8, 11, and 13 respectively. Wettability does not change in highly corrosive environment because the superhydrophobic coating was synthesized by a sol-gel, which is acidic. During the hydrolysis of PFOTS, HCl will form as the by-product. Additionally, the chemical inertness of SiO2 nanoparticles present in the coating also provides stability [41].
The durability of ultraviolet irradiation of synthesized superhydrophobic glass surfaces was also examined by exposure to the UV light, as reported [42]. The coating was exposed to more than 40 h of UV exposure. The superhydrophobicity of the surface does not change, and the static contact angle is found to be about 173° ± 1° and sliding angle 4° ± 0.5°. Additionally, coatings were preserved for over 3 months under the ambient conditions and revealed that there was no change in superhydrophobicity.
Fig. 6 shows microstructures of samples along with their EDS spectra before and after UV treatment. Fig. 6 (a) indicates the surface structures of untreated and treated samples reveal islands, while after a 40 hr treated sample also exhibits no change in the microstructure, this
9
also indicates there is no loss on its superhydrophobic nature. And also, Fig. 6 (b) confirms the elements were the same as before and after treatment.
Additionally, to further confirm the potential chemical changes in the UV-irradiated sample was analyzed with FTIR-spectra, and its results are reported in Fig.3 (UV effected peak). The C-H stretching peak found at 2953.94 cm−1 [37]. The various C=H and C=F bonds of PFOTS peaks were found in the region of 700 cm−1 in between of 1450 cm−1 [38]. C = O stretching and C-H asymmetric stretching of PMMA peaks was observed at 1732.07 cm−1 and 1383.37 cm−1, respectively [39]. Si-O-SH stretching and Si-O-Si bending vibrations were found at the peaks of 1096.60 cm−1 and 809.18 cm−1 and 466.30 cm−1, respectively [40]. The peaks were nearly similar when compared with the unaffected sample. Based on the unaltered peaks, it reveals the coating still existing the superhydrophobic nature even after UV treated.
The adhesion, abrasion, and water jet impact experiments were performed as early reported [29, 36, 42] for the mechanical durability of the coating. Fig. 7 (a) shows the tape peeling test on the superhydrophobic glass surface using insulated tape. Constant gluing and ungluing of insulated tape on the coated surface were studied while applying pressure. The study shows that the surface remains stable, upto 25 cycles of peeling. The static contact angle reduces to 125.1°± 5°, with a sliding angle higher than 90°, and the same has been depicted in Fig. 7 (d). It is due to the physisorption between substrate and coating materials; thus, the coating gets damaged, and the contact angle reduces and turns into a hydrophobic nature.
The micro-fiber cloth was served as an abrasion surface to investigate the mechanical damage to the superhydrophobic glass surface, as visualized in Fig. 7 (b). The weight if 20 g (0.2 N) was draped with abrasion surface, and then the coated glass surface was tested by the 10
opposite direction of the abrasion material. Simultaneously, a pressure of 1.130 kPa was given onto the surface of the coated glass area of 2 cm-2 in the front and back way. This route was notified as one abrasion cycle, and 170 cycles were performed. It is found that the coated surface bears superhydrophobicity upto 170 cycles abrasion. Nanda et al. [29] synthesized superhydrophobic coating on a glass slide with the use of OTS and silica microparticles, where the coating was able to withstand its superhydrophobicity for 4 abrasion cycles. When the present coating was synthesized with using of binder (PMMA) and SiNps, and it withstands upto 170 cycles of abrasion test; this may be due to no breakage of bonds between the coating materials. Soon after that, the continuous abrasion (180 cycles) was noticed on the surface; this resulted in sticky nature even after 90° tilting of the surface. The contact and sliding angles were measured respectively after the 180 cycles of abrasion and reported 116.9°± 5° and higher than 90°± 5°(Fig. 7 (d)). The superhydrophobic property vanished after 200 abrasion cycles. The abrasion test, it is indicating the suitable abrasive resistance of the coating, as per the results reported previously.
A water jet test was also carried by spraying water on to the coated glass surface (Fig. 7 (c)). Water has bounced back without leaving any traces of water drops on its surface due to the excellent water repellency nature of the fabricated surface. Further, it is also found that the superhydrophobicity is not affected by continuous water jet, and it does not change even after three minutes of spraying, and contact angle is found 171.5°± 1° and sliding angle is 5°± 1° (Fig. 7 (d)). It is signifying the outstanding mechanical strength of the coating.
3.3 The applications of superhydrophobic surfaces
3.3.1 Self-cleaning
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Self-cleaning property on the glass surface makes it is applicable in windshields, constructions, solar panels, automotive as it can decrease the price of maintenance and increases their lifespan. The as-created surface displays a high CA and low roll-off angle, permitting the water droplets to roll off easily. It can be presented by the evaluation method for a droplet of water tilting on the as-coated surface. Fig. 8 represents the self-cleaning effect of the uncoated and superhydrophobic glass surface using activated charcoal powder as a mimic for contamination. Water was then poured gently onto the surface to clean the dusted area; the powder stuck to the uncoated surface. Whereas superhydrophobic surface, hydrophilic dust gathered at the water surface due to its adhesion nature among water and dust. The dirt was able to roll off easily with water droplets from the contaminated surface and reveals the “roll-to-clean” behavior.
3.3.2 Transparency
In addition to water-repellent and self-cleaning properties of SiNps-PFOTS-PMMA coated glass, it also shows the transparency which was examined by UV-Vis transmittance spectra. In Fig.9. the image shows the transparent behavior of superhydrophobic glass along with an uncoated area. The good readability of the calligraphy beneath the superhydrophobic glass is mirrored its high transparency. Fig. 9. also shows the transmittance of uncoated and superhydrophobic glass in the range of 200 – 800 nm. The transmittance of coated glass is found more than 86% in the visible light region (400-800 nm). From the figure, the results show a coated glass of 86% and uncoated one is of 95% transmittance in the visible region, which is about 9% lower than that of bare glass (95 %). From these results, it can be concluded that the produced superhydrophobic coatings are suitable for windshields, buildings, solar panels, and automobiles applications.
4. Conclusions 12
In summary, the coatings on glass surfaces were developed by a simple dip-coating method using SiNps-PFOTS-PMMA composite. The wettability of the superhydrophobic surface is reached a static contact angle of 174° ± 2° along with a sliding angle 4 ± 1°. Surface morphology confirms the rough and hierarchical structures on the coated surface. Additionally, these superhydrophobic glass surfaces presented excellent stability at higher temperatures, acidic-alkali conditions, UV irradiation, long term durability, self-cleaning, and good transparency properties. The multipurpose superhydrophobic glass surfaces were easy to develop and which makes present coating suitable for optical lenses, windshields, solar panels, and glass ceilings. Credit Author Statement Sangeetha Sriram: Conceptualization, Methodology, Data curation, Writing- Original draft preparation, Visualization, Investigation. R.K.Singh: Supervision, Formal analysis. A.Kumar: Project administration, Supervision Conflict of interest None.
Acknowledgments
The authors are indebted to the Science & Engineering Research Board, Department of Science and Technology, Government of India (Grant No. CRG/2018/001277) for financial support.
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List of figures
Fig.1. Schematic illustration showing the procedure of superhydrophobic coating formation on glass surfaces with PMMA-SiNps and PFOTS silane.
Fig.2.Surface morphology of as received uncoated and coated glass samples at different magnifications along with water static contact angle (inset images). In higher magnification morphology, tightly packed, and non-spherical rough nano/microstructures along with pores
are present on the surface, and these microstructures provide the roughness to the surface. The resulting nano-micro hierarchical roughness on the coated glass surface is enhancing the superhydrophobicity. EDX spectrum indicates the presence of different traces of carbon, oxygen, silicon, fluorine, and chlorine on the coated glass, and oxygen, silicon, sodium, magnesium, and calcium on the uncoated glass surface, which further confirms the presence of a coating on the surface.
Fig.3. FTIR spectra of superhydrophobic and UV-irradiation affected glass samples
Fig.4. (a) Water static contact angle of the coating after 1 h annealing at different temperatures. (b) Surface morphologies of coating before and after annealing at 400°C. The coating retains its superhydrophobic property upto 380 °C, revealing the thermal stability of the coating. And (c) EDS analysis of before and after annealing the samples. Whereas the annealed sample was showing the
less amount of chlorine and carbon while compared with the non-annealed sample.
Fig. 5. Water static contact angle versus pH of the samples after 400 h immersion at different pH solutions, showing pH stability of coating.
Fig.6. (a) Surface morphology and contact angle (inset) of superhydrophobic glass surface before and after UV irradiation, demonstrating UV resistance of the coating. (b) EDS spectra of coated and treated samples, which confirms further no change of traces presented in the treated sample.
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Fig.7. Pictorial images of (a) adhesion tape peeling, (b) abrasion, (c) water jet-impact tests, and (d) water static contact angles after the mechanical disturbances. The study shows that the surface
remains stable, upto 25 cycles of peeling, and 170 cycles of abrasion test. The static contact angle reduces to 125.1°± 5°, and 116.9° ± 5° for adhesion and abrasion respectively. The jetimpact shows the water bounces back in the opposite direction from the surface due to its superhydrophobic nature.
Fig.8. Images are showing the self-cleaning property on the uncoated and coated glass surface, where the water droplet collected the dirt along with it while rolling down from the surface. Whereas such a phenomenon not seen on the uncoated surface.
Fig.9. UV-Vis spectrum of uncoated and coated glass transmittance. The optical image shows
the transparent coated glass along with the uncoated area.
21
Fig. 1. Schematic illustration showing the procedure of superhydrophobic coating formation on glass surfaces with PMMA-SiNps and PFOTS silane.
22
Fig. 2. Surface morphology of as received uncoated and coated glass samples at different magnifications along with water static contact angle (inset images). In higher magnification morphology, tightly packed, and non-spherical rough nano/microstructures along with pores
are present on the surface, and these microstructures provide the roughness to the surface. The resulting nano-micro hierarchical roughness on the coated glass surface is enhancing the superhydrophobicity. EDX spectrum indicates the presence of different traces of carbon, oxygen, silicon, fluorine, and chlorine on the coated glass, and oxygen, silicon, sodium, magnesium, and calcium on the uncoated glass surface, which further confirms the presence of a coating on the surface.
23
Fig. 3. FTIR spectra of superhydrophobic and UV-irradiation affected glass samples
24
Fig. 4. (a)Water static contact angle of the coating after 1 h annealing at different temperatures. (b) Surface morphologies of coating before and after annealing at 400°C. The coating retains its superhydrophobic property upto 380 °C, revealing the thermal stability of the coating. And (c) EDS analysis of before and after annealing the samples. Whereas the annealed sample was showing the
less amount of chlorine and carbon while compared with the non-annealed sample.
25
Fig. 5. Water static contact angle versus pH of the samples after 400 h immersion at different pH solutions, showing pH stability of coating.
26
Fig. 6. (a) Surface morphology and contact angle (inset)of superhydrophobic glass surface before and after UV irradiation, demonstrating UV resistance of the coating. (b) EDS spectra of coated and treated samples, which confirms further no change of traces presented in the treated sample.
27
Fig. 7. Pictorial images of (a) adhesion tape peeling, (b) abrasion, (c) water jet-impact tests, and (d) water static contact angles after the mechanical disturbances. The study shows that the surface
remains stable, upto 25 cycles of peeling, and 170 cycles of abrasion test. The static contact angle reduces to 125.1°± 5°, and 116.9° ± 5° for adhesion and abrasion respectively. The jetimpact shows the water bounces back in the opposite direction from the surface due to its superhydrophobic nature.
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Fig. 8. Images are showing the self-cleaning property on the uncoated and coated glass surface, where the water droplet collected the dirt along with it while rolling down from the surface. Whereas such a phenomenon not seen on the uncoated surface.
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Fig. 9. UV-Vis spectrum of uncoated and coated glass transmittance. The optical image shows the transparent coated glass along with the uncoated area.
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Abstract figure
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Silica and Silane based Polymer Composite Coating on Glass slide by Dip-coating Method Sangeetha Sriram , R.K. Singh , Aditya Kumar PII: DOI: Reference:
S2468-0230(19)30673-X https://doi.org/10.1016/j.surfin.2020.100472 SURFIN 100472
To appear in:
Surfaces and Interfaces
Received date: Revised date: Accepted date:
19 November 2019 4 February 2020 8 February 2020
Please cite this article as: Sangeetha Sriram , R.K. Singh , Aditya Kumar , Silica and Silane based Polymer Composite Coating on Glass slide by Dip-coating Method, Surfaces and Interfaces (2020), doi: https://doi.org/10.1016/j.surfin.2020.100472
This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. © 2020 Published by Elsevier B.V.
Highlights
The superhydrophobic coating on glass synthesized silica and silane-based polymer composite coating (SiNps, PFOTS, and PMMA)by dip-coating method
Examined surface morphologies, contact angles, and chemical compositions of coatings.
Coatings are thermal, chemical, mechanical, and UV stable.
Superhydrophobic glass exhibits the excellent self-cleaning property and 91% transparency
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Silica and Silane based Polymer Composite Coating on Glass slide by Dipcoating Method Sangeetha Sriram1*, R.K. Singh1, and Aditya Kumar2 1
Department of Chemical Engineering, National Institute of Technology Rourkela 769008,
Odisha, India 2
Department of Chemical Engineering, Indian Institute of Technology (ISM) Dhanbad,
826004, Jharkhand, India Abstract
Superhydrophobic coatings are widely used for various engineering applications, namely, self-cleaning and self-healing for engineering structures. Therefore, in recent decades, a number of industries have shown significant interest in the development of superhydrophobic coatings for various purposes. In view of the above demands, this study presents explicitly a cost-effective and facile method to fabricate superhydrophobic transparent coating on the glass. The superhydrophobic coating was prepared by dip-coating technique with sol-gel of polymethyl methacrylate-co-ethyl acrylate
polymer
(PMMA),
SiO2nanoparticles
(SiNps)
and
1H,
1H,
2H,
2H
perfluorooctyltrichlorosilane (PFOTS). Wettability, surface morphology, and the transparency of coating were investigated. Also, the stability of the coating was assessed at harsh conditions like annealing at high temperatures (40-400 °C), irradiation by UV light, and pH resistance at different alkali and acidic conditions (2-13), and mechanical durability by performing water-jet, abrasion and adhesion tests were studied. The coated glass exhibits a static water contact angle (CA) of 174 ± 2° and with a sliding angle (SA) of 4 ± 1°. Furthermore, the coating exhibits excellent self-cleaning property, and more than 91% of the transparency of the coating was assessed. All the results indicated that such type of coatings could also use for self-cleaning and transparent coatings at the industrial level.
Keywords: Superhydrophobicity; Silica and silane-based polymer coating; Stability & durability; Self-cleaning &Transparency;
*Corresponding author: [email protected](Sangeetha. Sriram)
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1. Introduction
Superhydrophobic surfaces are well defined as substrates that have apparent advancing or receding contact angle greater than 150° and roll-off angle lower than 10°. For past decade researchers from the academics, industrial scientists, and engineers are showing much more attention to the synthesis of superhydrophobic surfaces motivated by natural surfaces like a lotus leaf, insect legs, butterfly wings, animal fur, feathers [1-4]. There are many techniques available to fabricate the artificial superhydrophobic coatings such as dipcoating [5], etching [6], sol-gel technique [7], chemical vapor deposition [8, 9], solution immersion [10], spray coating[11], spin coating [12]. These surfaces are providing potential applications such as anti-fogging [13], self-cleaning [14, 15], anti-fouling [16], anti-corrosion [17], anti-bacterial [18], anti-icing [7], drag reduction [19], anti-reflective [20], and oil-water separations [21, 22].
Glass surfaces are using in various applications in day to day life. glass is the use of most common optical material for lenses, windshields, architectural windows, solar panels, eye-catching interior, exterior walls, and glass ceilings. Based on regular usage, these surfaces need cleaning and maintenance. This requires a transparent and dust-free protective superhydrophobic layer to reduce the cost, effort, and time. Many researchers have been reported the transparent coatings on glass substrates. For example, Ebert et al. fabricated transparent, superhydrophobic, and wear-resistant coatings on glass and plastic substrates with the use of different nanoparticles such as SiO2, ZnO, and ITO [23]. Wang et al. reported a transparent and anti-fingerprint superhydrophobic thin film using polyaniline nanofibers on steel with fluoro-thiol modification [24]. Yokoi et al. reported optically transparent superhydrophobic polyester mesh surface with enhanced mechanical abrasion resistance by
3
using a three-step process using perfluorooctyltrichlorosilane, perfluorodecyltrichlorosilane, and NaOH[25].
Recently, Li et al. described a one-step process to fabricate superhydrophobic coating with high transparency with the use of trimethoxypropylsilane and fumed silica nanoparticles on the glass surface [26]. Latthe et al. developed the superhydrophobic and self-cleaning coatings on glass substrate using silica-PMMA composite with methyltrimethoxysilane compound by sol-gel process technique [27]. Xu et al. fabricated raspberry-like SiO2 nanoparticles/ polystyrene by adding methacryloxypropyltrimethoxysilane to mini-emulsion polymerization of styrene [28]. Nanda et al. synthesized functionalized silica microparticles for self-cleaning applications on glass substrates with octadecyl trichlorosilane by employing the sol-gel method [29]. Chang et al. fabricated superhydrophobic films via deposition of raspberry-like fluorescent PS/CdTe/silica microspheres on glass substrates [30]. Guo et al. fabricated light-diffusing films for LED applications by strawberry-like PMMA/SiO2 composite microspheres [31].
The superhydrophobic coatings on glass substrates were created by Bravo et al. with the use of cationic solutions of poly (allylamine hydrochloride) and anionic solutions of silica nanoparticles and trichloroperfluorooctyl silane via chemical vapor deposition [32]. Xu et al. fabricated anti-reflective and superhydrophobic coatings on glass substrates with the use of hydrophobic hexamethyldisilazane and perfluorooctyltriethoxysilane modified hollow silica nanoparticles and PMMA via dip-coating method [33]. Li et al. synthesized the superhydrophobicity on glass substrates via layer-by-layer assembly, followed by the calcination
process
with
the
use
of
mesoporous
silica
nanoparticles,
perfluorooctyltriethoxysilane, and poly diallyldimethylammonium chloride [34]. Xu et al. fabricated superhydrophobic thin films on glass substrates with the use of different materials
4
like SiO2 nanoparticles and perfluorooctyltrichlorosilane (PFOTS) [20]. Suwan et al. synthesized the superhydrophobic films on glass substrates by employing dip-coating and spray-on coating techniques with the use of PMMA/SiO2 nanocomposite and PTOS silane compound [35]. Bayer has articulated in his review paper, that in order to reveal liquid repelling coatings with durability and wear resistance is a significant factor, where the surfaces will provide the technical and large scale applications, and reported different types of durability and wear resistance of the transparent superhydrophobic coatings [36].
The current work focuses on the development of silica and silane-based polymer composite coating (SiNps, PFOTS, and PMMA) on glass by a simple dip-coating method. Coating shows stable superhydrophobic nature under extreme conditions of elevated temperatures, acid and alkali environment, UV light irradiation, and mechanical disturbances. Self-cleaning and transparency of coating have also examined.
2. Materials and methods
2.1. Materials
PMMA (average Mn ~39,500 and average Mw ~101,000), SiO2 nanoparticles (1020 nm), and 1H, 1H, 2H, 2H perfluorooctyltrichlorosilane (PFOTS – silane coupler) (≥ 97% purity) were purchased from Sigma-Aldrich Co., USA. Microscopic glass slides (76 mm X 26 mm X 1.25 mm) were obtained from Borosil Glass Works Ltd., India. Toluene and propanol were procured from Merck Specialties, Private Limited, India. Millipore water (18.2 mΩ cm resistivity) was used. Before developing the coating, all the substrates were washed with the tap water first, and removing the impurities on the substrates were then washed by Millipore water in ultra-sonicator for 15 min. Later on, the substrates again washed with isopropanol and were cured in an oven for overnight at 40°C.
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2.2 Coating procedure
Fig. 1. is representing the schematic illustration of superhydrophobic coating on the glass slide. The silica and silane-based polymer composite coating solution were prepared by adding PMMA(2 %, wt/v) and SiNps(1 %, wt/v) in 40 ml of toluene and stirred at 45 °C for 25 min. To this mixture, PFOTS silane coupler (1%, v/v) was then added and further continued the stirring for 15 min. To get the uniform dispersion of sol-gel was further sonicated for 20 min by using ultrasonicator. The solution was then dip-coated on the glass surface, which was later dried in a hot air oven for 5 h at a temperature of 60 °C.
2.3 Characterizations
The static water contact angle (CA) of the samples at room temperature was measured with the Drop Shape Analyzer (DSA 25 Krüss GmbH, Hamburg, Germany). The surface morphologies of the specimens observed using scanning electron microscopy (SEM, Nova Nano SEM FEI, Hillsboro, Oregon, USA). The elemental analysis of the samples was done by energy dispersive X-ray spectroscopy (EDX, Nova Nano SEM FEI, Hillsboro, Oregon, USA). The surface roughness and thickness of the film (ASH- average step height) were evaluated by using a stylus profilometer instrument (Veesco Dektak 150) with Dektak 150 software. 4-7 µl volume range of single water droplet was used for measurements of CA. CA measurements were repeated at five different locations of each sample, and the average of CA was reported in this work. Functionalization of SiNps-PFOTS-PMMA analyzed by FTIR (Thermo Fisher Nicolet iS10) instrument. The transparency of the coated and bare glass was measured by a UV-Vis spectrophotometer (Jasco V-750 UV- visible spectrophotometer). 6
3. Results and discussion
3.1. Morphology and wettability
Cleaned uncoated silicon glass slide surface shows a water static contact angle of 32 ± 3°, and it’s in hydrophilic. After coating with silica and silane-based polymer composite coating, the static water contact angle of the coated sample is increased to 174 ± 2° and sliding angle 4 ± 1°, uncoated and coated samples surface morphologies were also studied by
SEM, images as shown in Fig. 2. The coated glass surface exhibits rough islands like morphology in the microstructure, while at higher magnification SEM photographs reveal clustered non-spherical rough nano/microstructures along with pores present on the surface, and these microstructures provide the roughness to the surface. The resulting nano-micro hierarchical roughness on the coated glass surface is enhancing the superhydrophobicity. Whereas the uncoated glass shows the plain surface without rough structures. Xu et al. reported similar surface morphology of micro/nanoscale hierarchical roughness for superhydrophobic coating on the glass, which was produced by using SiO2 nanoparticles, TEOS, and PFOTS [20]. The roughness and film thickness of the coated glass surface and uncoated glass using a stylus profilometer. The roughness is measured 6.2 ± 0.6 µm, and 2.9 ± 0.7 µm for coated and uncoated glass surface respectively. Film thickness was calculated by the average step height (ASH), and it is 6.60 ± 0.30 µm.
Further, EDX of both uncoated and uncoated glass was carried out, as shown in Fig. 2, and it confirms the presence of carbon, oxygen, silicon, fluorine, and chlorine on the coated glass, and oxygen, silicon, sodium, magnesium, and calcium on the uncoated glass 7
surface. The functionalization of SiNps-PFOTS-PMMA coating was also confirmed via IR spectra, as shown in Fig. 3 (coated peak).A peak at 2954 cm−1 corresponds to C-H stretching [37]. Peaks from 1450 to 700 cm−1are validated to the various C=H and C=F bonds of PFOTS [38]. The peak at 1735.23 cm−1 represents the C = O stretching. The peak at 1384.64 cm−1 shows the C-H asymmetric stretching of PMMA[39]. The frequency at 1098.74 cm−1and 807.74 cm−1 and 466.30 cm−1Si -O - SH stretching and Si-O-Si bending vibrations, respectively [40]. FTIR and EDX confirm the existence of low surface energy materials of PMMA, PFOTS, and SiNps on the coated glass. Through the optimal mixture of low surface energy material and roughness, coating shows the superhydrophobic nature.
3.2. Wetting stability of the coatings
For industrial and practical applications, superhydrophobic surfaces should last under extreme surroundings. So, the stability and durability of these surfaces were widely and systematically inspected under a sequence of extremely harsh conditions.
An approach of the annealing experiment was carried out using the method reported earlier [22]. The assessment of annealing was examined by exposing the coated glass samples to elevated temperatures. The coated samples were pre and post annealed for 1 h at different temperatures (40 to 400 °C). The CA was measured after cooling the samples. Fig.4 (a) indicates the water CA values against all annealing temperatures. It also shows the morphology of the uncoated and coated sample before and after annealing at 400 °C Fig. 4 (b). The CA 173° ± 1° and sliding angle of 3.2° ± 0.5° were unchanged up to an annealing temperature of 380 °C, and water droplet rolls from the surface. While at 400 °C, the sample loses its superhydrophobic nature, and it turns into hydrophobic as water contact angle reduced to 95.4°± 7° and sliding angle greater than 20°. And due to the sample surface degradation, and cracks were formed on the surface. EDS analysis was performed to observe 8
any change in the composition before and after annealing, from the EDS graph (fig 4(c)) data it has been noticed that chlorine percentage has declined in annealed condition than compared to the non-annealed condition. This could be due to desorption during annealing [20].
To examine the pH stability of the superhydrophobic coating was evaluated after immersing the samples in acid and alkali solutions of various pH (2, 5, 8, 11, and 13), as reported previously [29]. CA of samples at various pH after 400 h of dipping is shown in Fig.5. The wetting property of samples retained even after 400 h of immersion in the acid and alkali solutions, displaying the outstanding pH stability of the coating. The contact and sliding angles were measured and reported as 171.9° and <5 ± 0.6°, 171.2° and <5 ± 0.2°, 171.1° and <4 ± 0.5°, 171.0° and 4.2 ± 0.5°, and 169.3°and <4.8 ± 0.5°, for various pH 2, 5, 8, 11, and 13 respectively. Wettability does not change in highly corrosive environment because the superhydrophobic coating was synthesized by a sol-gel, which is acidic. During the hydrolysis of PFOTS, HCl will form as the by-product. Additionally, the chemical inertness of SiO2 nanoparticles present in the coating also provides stability [41].
The durability of ultraviolet irradiation of synthesized superhydrophobic glass surfaces was also examined by exposure to the UV light, as reported [42]. The coating was exposed to more than 40 h of UV exposure. The superhydrophobicity of the surface does not change, and the static contact angle is found to be about 173° ± 1° and sliding angle 4° ± 0.5°. Additionally, coatings were preserved for over 3 months under the ambient conditions and revealed that there was no change in superhydrophobicity.
Fig. 6 shows microstructures of samples along with their EDS spectra before and after UV treatment. Fig. 6 (a) indicates the surface structures of untreated and treated samples reveal islands, while after a 40 hr treated sample also exhibits no change in the microstructure, this
9
also indicates there is no loss on its superhydrophobic nature. And also, Fig. 6 (b) confirms the elements were the same as before and after treatment.
Additionally, to further confirm the potential chemical changes in the UV-irradiated sample was analyzed with FTIR-spectra, and its results are reported in Fig.3 (UV effected peak). The C-H stretching peak found at 2953.94 cm−1 [37]. The various C=H and C=F bonds of PFOTS peaks were found in the region of 700 cm−1 in between of 1450 cm−1 [38]. C = O stretching and C-H asymmetric stretching of PMMA peaks was observed at 1732.07 cm−1 and 1383.37 cm−1, respectively [39]. Si-O-SH stretching and Si-O-Si bending vibrations were found at the peaks of 1096.60 cm−1 and 809.18 cm−1 and 466.30 cm−1, respectively [40]. The peaks were nearly similar when compared with the unaffected sample. Based on the unaltered peaks, it reveals the coating still existing the superhydrophobic nature even after UV treated.
The adhesion, abrasion, and water jet impact experiments were performed as early reported [29, 36, 42] for the mechanical durability of the coating. Fig. 7 (a) shows the tape peeling test on the superhydrophobic glass surface using insulated tape. Constant gluing and ungluing of insulated tape on the coated surface were studied while applying pressure. The study shows that the surface remains stable, upto 25 cycles of peeling. The static contact angle reduces to 125.1°± 5°, with a sliding angle higher than 90°, and the same has been depicted in Fig. 7 (d). It is due to the physisorption between substrate and coating materials; thus, the coating gets damaged, and the contact angle reduces and turns into a hydrophobic nature.
The micro-fiber cloth was served as an abrasion surface to investigate the mechanical damage to the superhydrophobic glass surface, as visualized in Fig. 7 (b). The weight if 20 g (0.2 N) was draped with abrasion surface, and then the coated glass surface was tested by the 10
opposite direction of the abrasion material. Simultaneously, a pressure of 1.130 kPa was given onto the surface of the coated glass area of 2 cm-2 in the front and back way. This route was notified as one abrasion cycle, and 170 cycles were performed. It is found that the coated surface bears superhydrophobicity upto 170 cycles abrasion. Nanda et al. [29] synthesized superhydrophobic coating on a glass slide with the use of OTS and silica microparticles, where the coating was able to withstand its superhydrophobicity for 4 abrasion cycles. When the present coating was synthesized with using of binder (PMMA) and SiNps, and it withstands upto 170 cycles of abrasion test; this may be due to no breakage of bonds between the coating materials. Soon after that, the continuous abrasion (180 cycles) was noticed on the surface; this resulted in sticky nature even after 90° tilting of the surface. The contact and sliding angles were measured respectively after the 180 cycles of abrasion and reported 116.9°± 5° and higher than 90°± 5°(Fig. 7 (d)). The superhydrophobic property vanished after 200 abrasion cycles. The abrasion test, it is indicating the suitable abrasive resistance of the coating, as per the results reported previously.
A water jet test was also carried by spraying water on to the coated glass surface (Fig. 7 (c)). Water has bounced back without leaving any traces of water drops on its surface due to the excellent water repellency nature of the fabricated surface. Further, it is also found that the superhydrophobicity is not affected by continuous water jet, and it does not change even after three minutes of spraying, and contact angle is found 171.5°± 1° and sliding angle is 5°± 1° (Fig. 7 (d)). It is signifying the outstanding mechanical strength of the coating.
3.3 The applications of superhydrophobic surfaces
3.3.1 Self-cleaning
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Self-cleaning property on the glass surface makes it is applicable in windshields, constructions, solar panels, automotive as it can decrease the price of maintenance and increases their lifespan. The as-created surface displays a high CA and low roll-off angle, permitting the water droplets to roll off easily. It can be presented by the evaluation method for a droplet of water tilting on the as-coated surface. Fig. 8 represents the self-cleaning effect of the uncoated and superhydrophobic glass surface using activated charcoal powder as a mimic for contamination. Water was then poured gently onto the surface to clean the dusted area; the powder stuck to the uncoated surface. Whereas superhydrophobic surface, hydrophilic dust gathered at the water surface due to its adhesion nature among water and dust. The dirt was able to roll off easily with water droplets from the contaminated surface and reveals the “roll-to-clean” behavior.
3.3.2 Transparency
In addition to water-repellent and self-cleaning properties of SiNps-PFOTS-PMMA coated glass, it also shows the transparency which was examined by UV-Vis transmittance spectra. In Fig.9. the image shows the transparent behavior of superhydrophobic glass along with an uncoated area. The good readability of the calligraphy beneath the superhydrophobic glass is mirrored its high transparency. Fig. 9. also shows the transmittance of uncoated and superhydrophobic glass in the range of 200 – 800 nm. The transmittance of coated glass is found more than 86% in the visible light region (400-800 nm). From the figure, the results show a coated glass of 86% and uncoated one is of 95% transmittance in the visible region, which is about 9% lower than that of bare glass (95 %). From these results, it can be concluded that the produced superhydrophobic coatings are suitable for windshields, buildings, solar panels, and automobiles applications.
4. Conclusions 12
In summary, the coatings on glass surfaces were developed by a simple dip-coating method using SiNps-PFOTS-PMMA composite. The wettability of the superhydrophobic surface is reached a static contact angle of 174° ± 2° along with a sliding angle 4 ± 1°. Surface morphology confirms the rough and hierarchical structures on the coated surface. Additionally, these superhydrophobic glass surfaces presented excellent stability at higher temperatures, acidic-alkali conditions, UV irradiation, long term durability, self-cleaning, and good transparency properties. The multipurpose superhydrophobic glass surfaces were easy to develop and which makes present coating suitable for optical lenses, windshields, solar panels, and glass ceilings. Credit Author Statement Sangeetha Sriram: Conceptualization, Methodology, Data curation, Writing- Original draft preparation, Visualization, Investigation. R.K.Singh: Supervision, Formal analysis. A.Kumar: Project administration, Supervision Conflict of interest None.
Acknowledgments
The authors are indebted to the Science & Engineering Research Board, Department of Science and Technology, Government of India (Grant No. CRG/2018/001277) for financial support.
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List of figures
Fig.1. Schematic illustration showing the procedure of superhydrophobic coating formation on glass surfaces with PMMA-SiNps and PFOTS silane.
Fig.2.Surface morphology of as received uncoated and coated glass samples at different magnifications along with water static contact angle (inset images). In higher magnification morphology, tightly packed, and non-spherical rough nano/microstructures along with pores
are present on the surface, and these microstructures provide the roughness to the surface. The resulting nano-micro hierarchical roughness on the coated glass surface is enhancing the superhydrophobicity. EDX spectrum indicates the presence of different traces of carbon, oxygen, silicon, fluorine, and chlorine on the coated glass, and oxygen, silicon, sodium, magnesium, and calcium on the uncoated glass surface, which further confirms the presence of a coating on the surface.
Fig.3. FTIR spectra of superhydrophobic and UV-irradiation affected glass samples
Fig.4. (a) Water static contact angle of the coating after 1 h annealing at different temperatures. (b) Surface morphologies of coating before and after annealing at 400°C. The coating retains its superhydrophobic property upto 380 °C, revealing the thermal stability of the coating. And (c) EDS analysis of before and after annealing the samples. Whereas the annealed sample was showing the
less amount of chlorine and carbon while compared with the non-annealed sample.
Fig. 5. Water static contact angle versus pH of the samples after 400 h immersion at different pH solutions, showing pH stability of coating.
Fig.6. (a) Surface morphology and contact angle (inset) of superhydrophobic glass surface before and after UV irradiation, demonstrating UV resistance of the coating. (b) EDS spectra of coated and treated samples, which confirms further no change of traces presented in the treated sample.
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Fig.7. Pictorial images of (a) adhesion tape peeling, (b) abrasion, (c) water jet-impact tests, and (d) water static contact angles after the mechanical disturbances. The study shows that the surface
remains stable, upto 25 cycles of peeling, and 170 cycles of abrasion test. The static contact angle reduces to 125.1°± 5°, and 116.9° ± 5° for adhesion and abrasion respectively. The jetimpact shows the water bounces back in the opposite direction from the surface due to its superhydrophobic nature.
Fig.8. Images are showing the self-cleaning property on the uncoated and coated glass surface, where the water droplet collected the dirt along with it while rolling down from the surface. Whereas such a phenomenon not seen on the uncoated surface.
Fig.9. UV-Vis spectrum of uncoated and coated glass transmittance. The optical image shows
the transparent coated glass along with the uncoated area.
21
Fig. 1. Schematic illustration showing the procedure of superhydrophobic coating formation on glass surfaces with PMMA-SiNps and PFOTS silane.
22
Fig. 2. Surface morphology of as received uncoated and coated glass samples at different magnifications along with water static contact angle (inset images). In higher magnification morphology, tightly packed, and non-spherical rough nano/microstructures along with pores
are present on the surface, and these microstructures provide the roughness to the surface. The resulting nano-micro hierarchical roughness on the coated glass surface is enhancing the superhydrophobicity. EDX spectrum indicates the presence of different traces of carbon, oxygen, silicon, fluorine, and chlorine on the coated glass, and oxygen, silicon, sodium, magnesium, and calcium on the uncoated glass surface, which further confirms the presence of a coating on the surface.
23
Fig. 3. FTIR spectra of superhydrophobic and UV-irradiation affected glass samples
24
Fig. 4. (a)Water static contact angle of the coating after 1 h annealing at different temperatures. (b) Surface morphologies of coating before and after annealing at 400°C. The coating retains its superhydrophobic property upto 380 °C, revealing the thermal stability of the coating. And (c) EDS analysis of before and after annealing the samples. Whereas the annealed sample was showing the
less amount of chlorine and carbon while compared with the non-annealed sample.
25
Fig. 5. Water static contact angle versus pH of the samples after 400 h immersion at different pH solutions, showing pH stability of coating.
26
Fig. 6. (a) Surface morphology and contact angle (inset)of superhydrophobic glass surface before and after UV irradiation, demonstrating UV resistance of the coating. (b) EDS spectra of coated and treated samples, which confirms further no change of traces presented in the treated sample.
27
Fig. 7. Pictorial images of (a) adhesion tape peeling, (b) abrasion, (c) water jet-impact tests, and (d) water static contact angles after the mechanical disturbances. The study shows that the surface
remains stable, upto 25 cycles of peeling, and 170 cycles of abrasion test. The static contact angle reduces to 125.1°± 5°, and 116.9° ± 5° for adhesion and abrasion respectively. The jetimpact shows the water bounces back in the opposite direction from the surface due to its superhydrophobic nature.
28
Fig. 8. Images are showing the self-cleaning property on the uncoated and coated glass surface, where the water droplet collected the dirt along with it while rolling down from the surface. Whereas such a phenomenon not seen on the uncoated surface.
29
Fig. 9. UV-Vis spectrum of uncoated and coated glass transmittance. The optical image shows the transparent coated glass along with the uncoated area.
30
Abstract figure
31