Graphene-based Super-hydrophobic Coating

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ScienceDirect Materials Today: Proceedings 17 (2019) 752–760

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RAMM 2018

Preparation of a Polydimethylsiloxane (PDMS)/Graphene-based Super-hydrophobic Coating K. A. Saharudin, M. A. Karim, S. Sreekantan* School ofMaterials & Mineral Resources Engineering, Engineering Campus, Universiti Sains Malaysia, 14300 Nibong Tebal, Pulau Pinang, Malaysia

Abstract In this work, a facile method is proposed to fabricate a polydimethylsiloxane (PDMS)/graphene-based super-hydrophobic coating on glass surface via spraying method. Three different type of graphene such as graphene (G), graphene oxide (GO) and modified graphene oxide (mGO) was incorporated into PDMS to investigate the super-hydrophobicbehaviour. After being dried at 80 °C, the water contact angle (WCA) and sliding angle (SA) on the coating were tested to evaluate the wettability of the coating surface. Results showed that G-PDMS and mGO-PDMS has WCA of 159° and 162°, while the SA is 30° and 25°, respectively. GO-PDMS has lower WCA of 140° and SA is 90°. Durability of the super-hydrophobic coating film were evaluated via peel off test, UV aging and acid-base stability at pH 4 and pH 10. Peel of test shows, G-PDMS has better stability compare to GO-PDMS and mGO-PDMS. All the 3 films have better durability in basic environment than acidic environment. G-PDMS and mGOPDMS has better UV aging durability than GO-PDMS. © 2019 Elsevier Ltd. All rights reserved. Selection and peer-review under responsibility of the scientific committee of the 6th International Conference on Recent Advances in Materials, Minerals & Environment (RAMM) 2018. Keywords: PDMS; graphene oxide; superhydrophobic

*Corresponding author. Tel.: +6-04-599-5255; fax: +6-04-599-6907 E-mail address: [email protected]

2214-7853 © 2019 Elsevier Ltd. All rights reserved. Selection and peer-review under responsibility of the scientific committee of the 6th International Conference on Recent Advances in Materials, Minerals & Environment (RAMM) 2018.

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1. Introduction Super-hydrophobic surfaces are mainly fabricated by manipulating the interface property via two ways; 1) by creating a molecular-level variation of architecture to form a rough surface and 2) terminally attaching various low surface-energy organic monolayers (ex: silane functionalizing agents) to the surface [1]. These features allow water droplets to smoothly roll off from the surface[2]. The low sliding angle (SA) can be achieved by creating micro or nanostructured features, which can reduce the contact area between the surface and water droplet [3]. Application of ZnO [4], TiO2 [5], SiO2 [6], Al2O3 [7], CaCO3 [8] and SnO2 [9] nanoparticles could enhance the surface roughness, because aggregation of nanoparticles minimize the contact area, thus enhancing the super-hydrophobic behaviour. However, the use of graphene based materials are not well exploited although it has distinctive physicochemical properties such as high thermal conductivity, good thermal/chemical stability and exceptional mechanical modulus. Therefore, the use of G, GO and mGO particles was explored in this work. Another important aspect in fabrication of super-hydrophobic surface, is the use of low surface energy materials[10]. The high WCA can also be attained by lowering the surface free energy using silane functionalizing agents. There have been some reports on the preparation of super-hydrophobic surfaces using silane functionalizing agents. Liang et al., [11] developed a super-hydrophobic coating with tetraethylorthosilicate (TEOS) and vinyltriethoxysilane (VTES). The modified silica-based surface possessed the greatest static contact angle of 154.9°. Latthe et al. [12] developed a hydrophobic coating via a two-step process using methyltriethoxysilane (MTES) and trimethylethoxysilane (TMES). WCA of 120° was achieved with a SA of 9°. Huang et al., [13] fabricated superhydrophobic transparent surfaces by sol-gel method with silica-based coating in ethanol and subsequent coating of a low surface energy material 1H, 1H, 2H, 2H-perfluorooctyltrichlorosilane (PFDTS). The results showed that the coating had a WCA exceeding 160°, a SA lower than 10°. However, the long chain fluoro silanes are expensive and toxic [14] which bring potential risk to human health and environment [15]. Polydimetlylsiloxane (PDMS) – SiO2 [16, 17] mixture was also used to fabricate the super-hydrophobic surfaces with WCA of 140°–160° for catheters [18] and microvalves [19] where self-cleaning properties are important to avoid fouling. PDMS has low toxicity, high chemical stability, mechanical elasticity, long-term endurance and attractive transparency for outdoor applications [19]. Therefore, in this work PDMS was selected as surface functionalizing agent. The durability is one of the major concerns in super-hydrophobic coating fabrication. Only a few superhydrophobic coating has been reported to exhibit mechanical durability [20, 21]. Besides, the durability against chemical attack and UV aging is another requisite but has attained less attention so far. Therefore, in this investigation, we have fabricated graphene-based/PDMS coating on glass and mechanical, chemical and UV durability were assessed in order to form a good durable super-hydrophobic coatings. 2. Materials & Method 2.1. Materials Graphene nanopowder (11 – 15 nm) was provided by SkySpring Nanomaterials, Inc, US. Sulphuric acid (H2SO4), potassium permanganate (KMnO4), sodium hydroxide (NaOH) and ammonia solution (NH4OH) were all supplied by Merck, US. Polydimethylsiloxane (PDMS, average Mn ~ 550) and trimethylmethoxysialne (TMMS) were purchased from Sigma Aldrich, US. Hydrogen peroxide (~95%), acetone and ethanol were supplied by J.T. Baker, US. All the chemicals used as received without further purification and deionized water was used for all experiments and test. Microscope glass slides were supplied by Fisher Scientific. The glass slides were sonicated in ethanol for 5 min followed by immersing in NH4OH:H2O2:H2O (1:1:5) at 80 °C for 5 min to activate the reactive hydroxyl group on glass surface. This method is called as remote chemical analysis (RCA) cleaning, which is widely used in semiconductor industry [22]. 2.2. Preparation of grapheme oxide (GO) Graphene oxide was prepared by oxidation of graphene nanopowder according to Hummer’s method [23]. 25mL of concentrated H2SO4 was cooled to 4 °C. Under stirring mode at room temperature the cooled H2SO4 was slowly

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added to the graphene nanopowder (1 g) and KMnO4 (3 g) then heated to 50 °C for 3 h. 50 mL of water was slowly added to the mixture. During this process, temperature rises due to oxidation process. This is noticed by the colour changes from black to dark brown indicating successful formation of graphene oxide. Once the colour changes were completed, 5mL of H2O2 is added to remove the excessive amount of KMnO4 to stop the reaction. The obtained GO was oven dried overnight. 2.3. Preparation of TMMS modified graphene oxide (mGO) Since graphene oxide is hydrophilic in nature, therefore the surface has to be modified to possess hydrophobic behavior. To achieve the modification of GO, 5 mL of TMMS and 100 mL deionized water were firstly added to a 500-mL three-neck flask equipped with a mechanical stirrer and a condenser pipe, and then the pH value was adjusted to 4 by adding 1.8 mole H2SO4. After that, 60 mL of GO aqueous solution was added under stirring. Subsequently, the mixture was heated to 90 °C and kept for 6 h. Finally, the cooled mixture was filtrated, washed with plenty of deionized water, then dried in oven overnight at 80oC, and the black mGO was obtained for next use. 2.4. Preparation of super-hydrophobic PDMS/Graphene-based coating on glass 2.5 g of PDMS was stirred in 50 mL of acetone for 30 min to obtain a homogeneous dispersion. Next, 0.1 g of graphene (G) was added to the PDMS solution and sonicated for 30 min to form a homogenous solution. Similar procedure was repeated using GO and mGO. The weight ratio of graphene-based to PDMS was kept constant at 1:25. Subsequently, the hydrophobic solution was sprayed on the pretreated glass slide from 20 cm away with the help of a spraying gun (air pressure: 40 psi). The coated substrate was dried at 80 °C for 5 min in an oven. This procedure was repeated for 5 times with a time interval of 5 min. The coated glass was allowed to cure overnight at 80 °C in an oven. Finally, the glass was exposed to UV for 12 h. 2.5. Durability testing The peel-off adhesion test was carried out using a cellophane tape. The tape was laid across the coated surface and rubbed vigorously to ensure a good contact with the coating. Then, slowly pulled away from the sample at about 45 ° to the surface, and this process was repeated for 10 times at the same place using a new tape[24]. The chemical stability was investigated by immersing the coated glass substrate in a solution with different pH (range from 4 to 10) for 10 days. The surfaces were illuminated with UV (254 nm, 36 W) germicidal lamp to study the stability of hydrophobic coating against UV irradiation. 2.6. Characterization The surface morphology of the G, GO, mGO and super-hydrophobic glass were observed on field emission scanning electron microscopy (FESEM-EDX, Zeiss, Supra 35VP). The particle size distribution of all graphenebased powder were measured using Zetasizer Nano ZS90 (Malvern Panalytical). Fourier Transform Infrared (FTIR, Perkin Elmer) spectroscopy was used to investigate the functional groups of super-hydrophobic coating. The surface topology was characterized using an atomic force microscope (AFM, NanoNavi, SPA400) operated in contact mode. WCAs were measured with a contact angle goniometer (Rame hart Instrument. Co, USA) equipped with a video capture using about 5 μL of water drops as probe at room temperature, and at least five different positions were selected for measurement to calculate the average value. 3. Results and discussion A FESEM image of the graphene powder used in this work for the preparation of GO is presented in Fig. 1a. The image shows flake like structure resembling the layered structure of graphene. Meanwhile, FESEM image of GO and mGO are shown in Fig. 1b and c. Clearly, GO exhibited a lamellar form with more crumpled structure, whereas paper-like sheets accompanying with dense and folded regions were observed for mGO after modification with

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TMMS. The particle size distribution of G, GO and mGO were measured using zetasiser and the average particle size are 145, 117, and 1093 nm, respectively. The results affirm the larger size of the mGO after modification with TMMS.

Fig. 1. FESEM image represents the morphology of (a) G, (b) GO and (c) mGO

In the FTIR spectrum of the G (Fig. 2a), the peaks at ~3445 and 1639 cm-1 are attributed to –OH stretching vibrations and C=C skeletal vibrations of graphene sheets. Upon oxidation of G to GO, new band arise located at 1718, 1398, 1164 and 872 cm-1 representing C=O stretching, -OH vibration, C-O stretching, and C-H vibration, respectively (Fig. 2b). After modification, the intensity of the broad peak at 3445 cm-1 significantly decreased, and a new weak band at 2974cm-1 correspond to Si-O-C of TMMS appeared, confirming the successful grafting of TMMS on GO (Fig. 2c). The intensity of the absorption band at 1718cm-1 is corresponding to carbonyl C=O stretching that are hydrophilic in nature was also reduced. The absorption band at 1639 cm-1 ascribed to the skeletal vibrations C=C of graphitic domains still present. The absorption band at 1416 cm-1 and 776 cm-1 are attributed to C-H vibration was observed. The intense band at 1123 cm-1 which was attributed to alkoxy C-O stretching vibration were more intense compared to GO.

Fig. 2. FTIR spectra of (a) G, (b) GO and (c) Mgo

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GO was modified with TMMS to prepare mGO with better super hydrophobic wettability characteristic. Graphene Oxide (GO) has the moleculer structure with branches of OH and double bond O while TMMS has a molecular structure that contain of three C–Si–OR bond. Once TMMS has been hydrolysed to form –Si–OH groups via reaction within C–Si–OR and H ions from sulphuric acid. The OH branch from GO formed a hydrogen bonding with Si–OH from TMMS. The subsequent condensation process resulted in a formation of –R–Si–O–C bond, which is hydrophobic in nature. Fig. 3 provide the illustration of molecular structure changes from GO to mGO.

Fig. 3. The illustration of molecular structure of GO to mGO

It is well known that the construction of hierarchical micro/nanostructures is crucial for the achievement of superhydrophobic materials. The FESEM images and the corresponding 3D AFM images of the super-hydrophobic glass with G-PDMS, GO-PDMS and mGO-PDMS are presented in Fig. 4. The surface of G-PDMS coated glass are rough with protrusion which composed of agglomerates of graphene flake that densely packed 3D AFM images (Fig. 4aa) and representative line profile (Fig. 4ab) of G-PMDS shows the film is rough with repeated arrangement of peak and valleys. G-PDMS shows the Ra 508 nm and RMS roughness 759 nm. Such structure and roughness would be easier to achieve super hydrophobicity. With GO-PDMS (Fig. 4b), some surface was populated agglomerated GO. However, the surface is not packed densely packed with obvious periodic protrusion as seen in G-PDMS film. The surface roughness is rather low as compared to G-PDMS with less protrusion. The respective 3D AFM (Fig. 4ba) and line profile image shown in Fig. 4bb was in agreement with FESEM images whereby the average roughness dropped. Ra and RMS roughness was approximately 489 nm and 650 nm, respectively, which is much lower than G-PDMS. Reduced roughness might affect the wettability of the film for the possibility of trapping air are not feasible. Meanwhile, the mGO-PDMS coated glass possessed a hierarchical micro/nanostructure structure (Fig. 4c). The hierarchical formation is probably due to hydrolysis of PDMS with methyl functional group on surface of mGO, which makes the surface aggregation of microparticles to form hierarchical surface. However, the surface is not packed densely as seen in G-PDMS. These could be due to lack of PDMS to bond with bigger particles size of mGO as compared to G. The roughness was further confirmed further by 3D AFM images (Fig. 4ca). The results show similar trend to FESEM images whereby the average roughness Ra and RMS roughness was approximately 779 nm and 983 nm, respectively, which is much higher than G-PDMS and GO-PDMS. The obtained results and the line profile (Fig. 4cb) clearly showed the rough surface was created by the formation of hierarchical surface morphology.

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Fig. 4. FESEM images of (a) G-PDMS, (b) GO-PDMS and (c) mGO-PDMS. Images at the right side show the 3D AFM topographical images (aa,ba and ca of the corresponding coated glass). Images at the bottom (ab, bb and cb) show the line profile.

Table 1 shows the wetting behavior of G-PDMS, GO-PDMS and mGO-PDMS coated glass. As seen the WCA of G-PDMS coated glass is 159o ± 1o with SA of 30o. The wetting behavior of a surface is explained by two different states; 1) Wenzel state whereby the water droplets are entrapped in the voids and pinned tightly on the rough surface and the 2) Cassie-Baxter state which, the water droplets are suspended on the top asperities of the rough surface due to entrapped air cushions in the cavities, thus easy to roll. The results of graphene-PDMS shows the water droplet dragged across the film and started to roll off at SA 1 ± 1° and completely roll off at a SA 30 ± 1°. This suggests that the glass is able to repel water droplet at low SA, suggesting the coated surface is in Cassie-Baxter state. This is mainly attributed to the nature of surface morphology promoted by graphene flakes nature (as seen in line profile of Fig. 4ab) that led to air voids, thus suspend water droplets and ease the rolling actions. Table 1. Images of water droplet, WCA and SA of G-PDMS, GO-PDMS and mGO-PDMS coated glass. Substrate

Image of static water droplet

WCA (°)

SA (°) Started to roll

Complete roll off

G-PDMS

159 ± 1

1±1

30 ± 1

GO-PDMS

140 ± 1

15 ± 1

90 ± 1

mGO-PDMS

161 ± 1

1±1

25 ± 1

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As predicted, the WCA of the GO-PDMS coated glass is lower than G-PDMS; 140o ± 1o, reflecting hydrophobic nature instead of super-hydrophobic. The SA of the film with GO-PDMS is 90o. The water droplet is pinned when dragged over the coated surface and therefore SA is increased. The droplet is started to roll over the surface at a SA of 15 ± 1° and it is eventually roll off at a SA of 90 ± 1°. The pinning and roll off characteristics of water droplets on GO-PDMS support a mixed state of Wenzel + Cassie-Baxter. This may be ascribed to the less roughness that reduced the air trapping between the protrusions, which increases the pinning of water droplet. Such condition may cause the penetration of water droplets into the microstructure, resulting in Wenzel state but when the droplet is moving, it is readily repelled, resulting in Cassie-Baxter state. Hence, it can be concluded that GO-PDMS coated glass is dominated by a mixed state. Besides, the deterioration in the super hydrophobic behavior in GO-PDMS is caused by the existence of more polar hydroxyl, carboxyl and carbonyl group as shown in FTIR analysis. These polar group is not appropriate for preparing super-hydrophobic materials. However, the presence of hydroxyl and carbonyl group as reactive points, GO can be easily modified to achieve hydrophobicity. As expected, the mGO-PDMS film coated on the glass substrate had better super-hydrophobicbehaviour as compared to GO-PDMS. The WCA of the mGO-PDMS film is 161o ± 1o, reflecting super hydrophobic nature of the film. The results of mGO-PDMS shows the water droplet dragged across the film and started to roll off at SA 1 ± 1° and completely roll off at a SA 25 ± 1°. The SA was reduced from 90o (GO-PDMS) to 25o for mGO-PDMS. This suggests that the film is able to repel water droplet at low SA, suggesting the coated surface is in Cassie-Baxter state. This is mainly attributed to the nature of surface morphology which is in hierarchical form with high roughness (as seen in line profile of Fig. 4cb). This would have led to trapping of air voids, thus suspend water droplets and ease the rolling actions. The peel off test was conducted based on work reported by [24]. The peel off was repeated for 25 times on GPDMS, GO-PDMS and mGO-PDMS coated film on glass and the result of WCA after every 5 peel off is summarised in Table 2. The WCA angle varied from 159o to 161o for G-PDMS. There is no remarkable changes in WCA after 25 times of peel-off tape test, indicating the excellent adherence of the super-hydrophobic coating. The WCA angle varied for GO-PDMS varied from 140o to 146o, indicating moderate adherence of the GO-PDMS film on the glass substrate. In fact, there is higher variation (by 6o) in WCA after 25 times of peel-off tape test as compared to G-PDMS (by 3o), indicating there are much more unbond nanoparticles on the surface of the film. This is obvious with the higher amount of nanoparticles found onto the peeled off tape surface. The increase trend in WCA value could be due to the pull out effect of the unbond particles that create high surface roughness (Fig. 4a). As for mGO, the adherence of the sample was very poor and upon first peel off, the major region of the film were removed. More nano-particles were transferred onto the tape surface, suggesting insufficient crosslinking of PDMS to form three dimensional crosslink network structure. Therefore, it is suggested to improve the formulation with more PDMS content to ensure closely connected 3D network is formed. Table 2. WCA of G-PDMS, GO-PDMS and mGO-PDMS coated glass after peel-off test Peel-off times

Sample G-PDMS

GO-PDMS

mGO-PDMS

0

159 ± 1

140 ± 1

161 ± 1

5

159 ± 2

140 ± 1

-

10

160 ± 2

143 ± 2

-

15

160 ± 1

146 ± 2

-

20

161 ± 2

146 ± 2

-

25

161 ± 2

146 ± 1

-

The stability of a super-hydrophobic surface is an important factor for its practical application. The chemical stability of G-PDMS, GO-PDMS and mGO-PDMS coating was analyzed by immersing the glass substrates in aqueous solution at three different pH (4 and 10) for 20 days. Every 5 days, the WCA is analysed. pH values were selected by considering the acid rain (pH of 4) and washing liquid (pH of 10). The result is summarised in Table 3.

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It is observed that G-PDMS, GO-PDMS and mGO-PDMS are more susceptible to immersion test in acid as compared to base. After 20 days of immersion, the WCA for G-PDMS film in acid dropped by 45o and in base by 8o while for GO-PDMS film, reduced by 71o in acid and 4o in base and mGO-PDMS film dropped tremendously by 106o in acid and 29o in base. The drastic drop of the WCA in sample immersed in acidic environment could be due to the hydrogen ion from the solution that readily react with carboxyl groups thus induce protonation and make the film to become more hydrophilic in nature. Conversely, the less drop in WCA in basic condition is because the carboxyl group are deprotonated in basic media that rich with hydroxyl ion, thus induce less hydrophilicity as compared to acid. Since the presence of carboxyl group is relatively high for GO as compared to graphene, GPDMS are most stable in acid and base as compared to GO-PDMS. The significant dropped in WCA of mGOPDMS is not well understood and subject to ongoing studies. However, these could be due to the lack of PDMS content in current formulation that failed to form compact 3D network, thus provide sufficient pits for acid and base penetration through the film to deteriorate the super hydrophobic characteristic. Table 3. WCA of G-PDMS, GO-PDMS and mGO-PDMS coated glass after immersion in pH 4 and pH 10 Day

Sample immersed in pH 4

Day 0

Sample immersed in pH 10

G-PDMS

GO-PDMS

mGO-PDMS

G-PDMS

GO-PDMS

mGO-PDMS

159 ± 1

138 ± 2

162 ±1

159 ± 1

139 ± 1

162 ± 1

Day 5

143 ± 1

122 ± 2

89 ± 2

157 ± 1

137 ± 1

142 ± 1

Day 10

134 ± 1

87 ± 3

74 ± 3

157 ± 1

137 ± 1

140 ± 2

Day 15

132 ± 1

80 ± 3

59 ± 3

155 ± 1

135 ± 1

138 ± 1

Day 20

114 ± 2

67 ± 2

56 ± 2

151 ± 1

134 ± 1

133 ± 1

WCA variation after 20 days

45

71

106

8

4

29

UV stability of the super-hydrophobic coatings is extremely vital for exterior surfaces. In order to assess the UVstability, G-PDMS, GO-PDMS and mGO-PDMS coated glass substrate was exposed to UV light irradiation for 60 hours. Every 12 hours, the WCA of the coating was analysed and the results is tabulated in Table 4. As seen, G-PDMS and mGO-PDMS has better resistance to UV exposure rather than GO-PDMS. This is probably due to the tightly packed graphene particles due to the oxidation of PDMS. Upon prolonged UV irradiation, PDMS is gradually oxidized and the CH3-Si-O fragments are transformed into a stable –O-Si-O network with high bond strength. Table 4. WCA of G-PDMS, GO-PDMS and mGO-PDMS coated glass after UV aging Time (h)

Sample G-PDMS

GO-PDMS

mGO-PDMS

0

158 ± 1

140 ± 1

161 ± 1

12

157 ± 1

137 ± 2

158 ± 1

24

157 ± 1

122 ± 2

158 ± 2

36

155 ± 2

121 ± 2

157 ± 1

48

154 ± 1

117 ± 2

158 ± 2

60

154 ± 2

109 ± 2

157 ± 2

WCA variation after 60 h exposure

4

31

5

Conclusion In summary, GO and mGO nanoparticles have been successfully synthesized using Hummer method and modified with TMMS. Super-hydrophobic coating with excellent adhesion on glass has been successfully developed using graphene-based particles and PDMS via a facile spray coating and UV cured method. mGO-PDMS coated

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glass exhibited high surface roughness (983 nm with WCA of 161 ± 1°) when compared to G-PDMS (759 nm with WCA of 158 ± 1°) and GO-PDMS (650 nm with WCA of 140 ± 1°). mGO-PDMS has low surface energy and high roughness on glass, thus offer high degree of super-hydrophobicity. However, peel of test shows that mGO-PDMS has poor adherence as compared to G-PDMS and GO-PDMS. All the 3 films has better durability in basic environment than acidic environment. For UV aging, G-PDMS and mGO-PDMS has better durability than GOPDMS. Overall, the hydrophobicity of graphene-based/PDMS coating is in the order of G-PDMS > mGO-PDMS > GO-PDMS. Acknowledgements The authors are thankful to the Ministry of Education (MOE) Malaysia for funding this work under Transdisciplinary Research Grant Scheme (TRGS) grant no. 6769002. The authors are very much grateful to Universiti Sains Malaysia (USM) for providing the necessary facilities to carry out the research work. References [1] L. Feng, S. Li, Y. Li, H. Li, L. Zhang, J. Zhai, Y. Song, B. Liu, L. Jiang, D. Zhu, Advanced materials 14 (2002) 1857-1860. [2] H.Y. Erbil, A.L. Demirel, Y. Avcı, O. Mert, Science 299 (2003) 1377-1380. [3] B.A. Elman, Civil examinations and meritocracy in late imperial China, Harvard University Press 2013. [4] G. Kwak, M. Seol, Y. Tak, K. Yong, The Journal of Physical Chemistry C 113 (2009) 12085-12089. [5] J. Jiang, J. Xu, Z. Liu, L. Deng, B. Sun, S. Liu, L. Wang, H. Liu, Applied Surface Science 347 (2015) 591-595. [6] X. Zhang, F. Wang, L. Wang, Y. Lin, J. Zhu, Dyes and Pigments 138 (2017) 182-189. [7] I. Karapanagiotis, P.N. Manoudis, A. Savva, C. Panayiotou, Surface and Interface Analysis 44 (2012) 870-875. [8] Z. Yuan, J. Bin, M. Wang, J. Huang, C. Peng, S. Xing, J. Xiao, J. Zeng, X. Xiao, X. Fu, Surface and Coatings Technology 254 (2014) 97-103. [9] P.N. Manoudis, I. Karapanagiotis, Progress in Organic Coatings 77 (2014) 331-338. [10] X. Liao, H. Li, L. Zhang, X. Su, X. Lai, X. Zeng, Progress in Organic Coatings 115 (2018) 172-180. [11] J. Liang, Y. Hu, Y. Wu, H. Chen, Surface and Coatings Technology 240 (2014) 145-153. [12] S.S. Latthe, S.L. Dhere, C. Kappenstein, H. Imai, V. Ganesan, A.V. Rao, P.B. Wagh, S.C. Gupta, Applied Surface Science 256 (2010) 32593264. [13] W.-H. Huang, C.-S. Lin, Applied Surface Science 305 (2014) 702-709. [14] K. Prevedouros, I.T. Cousins, R.C. Buck, S.H. Korzeniowski, Environmental science & technology 40 (2006) 32-44. [15] C.-H. Xue, Y.-R. Li, P. Zhang, J.-Z. Ma, S.-T. Jia, ACS applied materials & interfaces 6 (2014) 10153-10161. [16] J. Bravo, L. Zhai, Z. Wu, R.E. Cohen, M.F. Rubner, Langmuir : the ACS journal of surfaces and colloids 23 (2007) 7293-7298. [17] Z. He, M. Ma, X. Xu, J. Wang, F. Chen, H. Deng, K. Wang, Q. Zhang, Q. Fu, Applied Surface Science 258 (2012) 2544-2550. [18] D. Rosato, Polymers, processes and properties of medical plastics: including markets and applications, Biocompatible Polymers, Metals, and Composites. Lancaster PA: Technomic Publ (1983) 1019-67. [19] X. Wu, S.-H. Kim, C.-H. Ji, M.G. Allen, Journal of Micromechanics and Microengineering 21(9) (2011) 095003. [20] Y. Zhang, D. Ge, S. Yang, Journal of colloid and interface science 423 (2014) 101-107. [21] J.H. Li, R. Weng, X.Q. Di, Z.W. Yao, Journal of Applied Polymer Science 131 (2014). [22] T. Dey, D. Naughton, Journal of Sol-Gel Science and Technology 77 (2016) 1-27. [23] D.C. Marcano, D.V. Kosynkin, J.M. Berlin, A. Sinitskii, Z. Sun, A. Slesarev, L.B. Alemany, W. Lu, J.M. Tour, ACS nano 4 (2010) 48064814. [24] J. Wang, G. Wu, J. Shen, T. Yang, Q. Zhang, B. Zhou, Z. Deng, B. Fan, D. Zhou, F. Zhang, Journal of sol-gel science and technology 18 (2000) 219-224.