A Superhydrophobic Coating with Sturdy Abrasion and Weather Resistance

doi:10.21203/rs.3.rs-4372741/v1

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A Superhydrophobic Coating with Sturdy Abrasion and Weather Resistance

https://doi.org/10.21203/rs.3.rs-4372741/v1

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published 17 Jun, 2024

Read the published version in Journal of Inorganic and Organometallic Polymers and Materials →

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Here, we developed a lotus-leaf-resembling superhydrophobic coating with sturdy abrasion and weather resistance. By taking the sturdiness of the superhydrophobicity into account, this coating was created by incorporating a zinc-mediated superhydrophobic surface that was rough and ultraviolet-resistant into a polyurethane layer capable of strong wear resistance. By spraying the zinc-mediated perfluorosilane and a polyurethane suspension onto an aluminum flake, the lotus-leaf-resembling superhydrophobic coating was thus prepared. The resulting coating displayed the natural superhydrophobic phenomena with a contact angle of up to 157.1° and a rolling angle of 4.2°, greater or smaller by depending on the dosage of zinc. The adoption of zinc to the prepared coating not only mediated the rough surface texture but also extra granted the ultraviolet resistance. In couple with the strong wear resistance of the substrate layer, the proposed superhydrophobic coating provided the expected sturdy abrasion and weather resistance. The development of the superhydrophobic coating shares a prospect with practical applications, especially outdoor applications.

Polyurethane coatings

superhydrophobicity

abrasion

weather resistance

Lotus leaves are often recognized as a symbol of purity and have unique superhydrophobic properties that allow water droplets to freely roll off the surfaces and to take away dust and impurities from the surfaces (i.e., " lotus effect"). On this account, the lotus-leaf-resembling superhydrophobic coatings have vigorously shown their uniqueness and functionality in applications, such as dewatering, defogging, anti-icing, anti-fouling and self-cleaning properties [1–3]. The essence behind the uniqueness and functionality is the rough surface textures of lotus leaves which contain micro- and nano-sized structures (somewhat like "peaks" and "valleys" in maintains). These "peaks" and "valleys" could aid in preventing water from touching the surfaces of lotus leaves, allowing water to remove dust and impurities from the surfaces. As such, the lotus-leaf-resembling superhydrophobic coatings have assumed valuable applications in electric appliances, pipeline transportation, power grids, ships, automobiles, and medical equipment, etc [4–6].

Superhydrophobic phenomena are also visible in other natural tissues and beings in addition to lotus leaves, such as roses, butterfly wings, water striders and leaves of various plants [7–10]. These superhydrophobic phenomena are now generally mentioned as the "lotus effect" which often displays a contact angle higher than 150° and a rolling angle lower than 10°. With respect to the fabrication of the superhydrophobic coatings, the common points are the combination of the rough surface textures with the hydrophobic substrate layers. Over the past few years, a rapidly-growing quantity of superhydrophobic coatings has been reported [11, 12]. Nonetheless, these existing and ongoing endeavors do not necessarily lead to valuable applications, given the fact that most of these paradigms do not purposefully aim at practical applications and especially outdoor applications which typically require anti-ultraviolet properties, strong wear and corrosion resistance, besides the superhydrophobic ability.

As far as the dilemma are concerned, it is crucial to provide the prepared superhydrophobic coatings with sturdy abrasion and weather resistance (typically like the anti-ultraviolet properties and the wear resistance). To this point, the recent studies imply that adding transition-metal oxides into coatings and using wearable polymers as the substrate layer might help address the dilemma [13, 14]. The addition of transition-metal oxides to coatings can help formulate the anti-ultraviolet properties, given the inherent ultraviolet absorption in these oxides themselves [15, 16]. The use of wearable polymers as the substrate layer may help induce wearing quality due to the strong wear resistance in the polymers (such as polyurethane) [17, 18]. Although these outcomes can not be straightforwardly applied to fabricate superhydrophobic coatings (given the difficulty on processing these metal oxides), the incorporation of transition-metal oxides to wearable polymers suggests a prospect to develop superhydrophobic coatings with sturdy abrasion and weather resistance.

Here, we report an exploratory work on developing a superhydrophobic coating with sturdy abrasion and weather resistance. This lotus-leaf-resembling coating was fabricated by incorporating a zinc-mediated superhydrophobic surface that was rough and ultraviolet-resistant into a polyurethane layer capable of strong wear resistance. The addition of zinc into the prepared coating not only mediated the rough surface texture but also extra granted the ultraviolet resistance. In couple with the strong wear resistance of the substrate layer, the proposed superhydrophobic coating provided the expected sturdy abrasion and weather resistance. As such, the proposed coating suggests a prospect for practical application, and especially outdoor applications.

2.1. Materials

The chemicals used are of analytical reagents and adopted as commercially received. Zinc oxide (20 nm), silica (60 nm), ethylene glycol diglycidyl ether, heptadecafluorodecyltriethoxysilane (FAS17), 3-aminopropyltriethoxysilane (KH550) and polyurethane were achieved from Shanghai Maclean Biochem Technol Co. (China). Anhydrous alcohol, ammonia (~ 25 wt-%) and aluminum flakes (70 mm×30 mm×0.5 mm) were purchased from Sinopharm (China).

2.2. Preparation of coating suspensions

Scheme 1 displays the technical outline for fabricating the proposed superhydrophobic coating. The zinc suspension and the polyurethane suspension were first prepared prior to fabricating the proposed coating. The zinc suspension was achieved under sonication by dispersing a certain amount of zinc oxide (1.2 g) in ethanol (15 mL), followed by adding silica (1.2 g), KH550 (0.25 g) and ammonia (2 mL) to form the suspension [19]. After a half hour's stirring, the resulting suspension was added with FAS17 (0.35 g) and then further kept stirring for 1 hour.

Using the identical program, the polyurethane suspension was achieved comparably by dissolving polyurethane (2.4 g) in ethanol (15 mL), followed by adding KH550 (0.25 g) and water (2 mL) to form the substrate suspension [20]. After a half hour's stirring, the resulting suspension was added with ethylene glycol diglycidyl ether (0.5 g) and then further kept stirring for 1 hour. In this way, the two kinds of suspension were prepared in place.

Scheme 1. Technical outline for fabricating the proposed superhydrophobic coating

2.3. Fabrication of superhydrophobic coatings

The zinc suspension and the polyurethane suspension were well mixed in a volume ratio of 1:1 with sonication before running spray. By holding the resulting suspensions (2 mL), the sprayer was pressed and sprayed towards an aluminum flake (distance: 10 cm). The resulting aluminum flake was laid at 60°C for 2 hours. The prepared superhydrophobic coating (i.e., the proposed coating) was named "Zn@PUC" (in which "Zn" represents the zinc-mediated coating ("C" in "PUC") and "PU" means the polyurethane substrate layer). For a comparative purpose, the control coating was comparably prepared but without using zinc oxide (named "N@PUC", where "N" suggests no use of zinc oxide).

2.4. Analysis and characterization

With modern tools, the analysis and characterization of the prepared coatings was run at the room temperature. The Fourier transform infrared (FTIR) spectra were scanned and recorded with an IRTracer-100 spectrophotometer (Japan). The scanning electron microscope (SEM) images were snapped with a FlexSEM 1000 II apparatus (Japan). The X-ray photoelectron spectroscopy (XPS) was detected using a Thermo Fisher K-Alpha X-ray photoelectron spectrometer that was attached with an Al K-Alpha source (E = 1486.6 eV) (USA). The energy dispersive X-ray (EDX) profiles were recorded using an EDX 7200 instrument (Japan). The spectra of ultraviolet absorption were recorded with a UV-9000 spectrophotometer (China).

2.5. Superhydrophobic angles

The superhydrophobic angles including the contact angles and the rolling angles were detected using a JCY-2 apparatus (China). 5 µL of water droplets were dropped onto the surfaces of the prepared coatings. After lying still up to equilibrium, the prepared coatings were detected with the contact angles using an attached imaging system. The rolling angles were further detected by inclining the aluminum flakes up to rolling of these water droplets [21]. These measurements were repeatedly run with six cycles and finally the average values were shown.

2.6. Ultraviolet resistance

The ultraviolet resistance of the prepared coatings was tested using a ZF-7 UV analyzer (China). Before detecting the contact angles, the prepared coatings were subject to the ultraviolet radiation (wavelength: 254 nm; power density: 120 µW cm^− 2) for up to 80 minutes. The ultraviolet resistance of the prepared coatings was achieved by contrasting the contact angles of the original samples with the radiated samples.

2.7. Abrasion resistance

The abrasion resistance of the prepared coatings was studied with both the tape-peeling testing and the sandpaper friction. For the tape-peeling testing, the coating surfaces were repeatedly stripped with a tape. For the sandpaper friction testing, the coating surfaces were rubbed repeatedly against a piece of sandpaper. After the abrasive surfaces were rinsed with anhydrous alcohol and dried from flowing air, the contact angles of the prepared coatings were detected.

2.8. Anti-corrosion properties

The anti-corrosion properties were detected, on one hand, by immersing the prepared coatings into hydrochloric acid (pH 1.0) and sodium hydroxide (pH 13.0) solutions. After the surfaces were rinsed with anhydrous alcohol and dried from flowing air, the contact angles of the prepared coatings were detected.

The anti-corrosion properties were detected, on the other hand, by immersing the prepared coatings into sodium chloride solution (3.5 wt-%), and then the electrochemical impedance spectra were detected using a CH1760E workstation. During the testing, three electrodes were configured in which the working electrode was covered with the prepared coatings (area: 7.1 cm²; thickness: ~100 µm) and the saturated calomel ran as the reference electrode, along with a platinum wire used as the counter electrode.

2.9. Self-cleaning properties

The self-cleaning functions of the prepared coatings were analyzed by staining the coating materials with coffee powder and methylene blue. The prepared coatings covered over aluminum flakes were inclined and then washed with a certain amount of water released from a quantitative tube. The washing process of the prepared coatings was taken pictures using a digital camera.

3.1. Analysis and characterization

The proposed superhydrophobic coating was fabricated, as explained, by spraying the mixture of the zinc suspension and the polyurethane suspension onto an aluminum flake. After fixed with polymerization, the proposed coating with a zinc-mediated surface was thus formed. Figures 1–5 show the analysis and characterization of the prepared coating materials. For the comparative discussion, the control coating prepared in the absence of zinc was also displayed together. The proposed coating revealed a few principal bands at 3100–3750 cm^− 1, 2900–3000 cm^− 1, ~ 1750 cm^− 1, 1650–1750 cm^− 1, and 1000–1300 cm^− 1, plus a few fingerprint bands (Fig. 1). These principal and fingerprint bands may be spectroscopically connected to the stretching O-H (F-H), N-H (C-H), C = O, Si-O and Zn-O bonds and their corresponding rotation [15, 16]. The incorporation of zinc oxide into the proposed coating evidently displayed Zn-O bands in comparison to the control coating. This outcome suggests that the proposed coating was prepared in consistence with the preparation process (cf. Sections 2.2 and 2.3). The EDX profiles (Fig. 2) and the XPS spectra (Fig. 3) upheld the FTIR analysis and manifested the element composition of C, N, O, F, Si and Zn. Figure 4 further refines the energy effect of zinc on the proposed coating, where silicon (2p) was tentatively considered due to the narrowest band that may eliminate overlapping and accordingly avert the complicated analysis. The incorporation of zinc into the proposed coating decreased the binding energy by 0.16 eV, implying the active electronic properties of zinc which may help induce anti-ultraviolet properties. Figure 5 shows the SEM imaging of the coating surfaces. The incorporation of zinc oxide into the proposed coating increased the roughness of the surface. The proposed coating was prepared in the desired form. Hence, the proposed coating is desired to have stronger superhydrophobicity and weather resistance. In the context, the further studies were performed.

Figure 1. The FTIR spectra of the prepared coating materials

Figure 2. The EDX profiles of the prepared coating materials

Figure 3. The XPS spectra of the prepared coating materials

Figure 4. The XPS spectra of silicon from the prepared coating materials

Figure 5. The SEM imaging of the surfaces of the prepared coatings (a: N@PUC; b: Zn@PUC)

3.2. Superhydrophobic properties

Figure 6 and Fig. 7 present the superhydrophobic phenomena of the prepared coatings. The proposed coating showed a contact angle as large as 157.1° and a rolling angle as small as 4.2°. By comparison, the control coating only revealed a contact angle 141.8° and a rolling angle 16.1°. The proposed coating authenticated the typical superhydrophobic phenomena but the control coating felt failure. The incorporation of zinc oxide into the proposed coating caused the occurrence of the superhydrophobic phenomena. This can be attributed to the mediated surface texture of zinc oxide in the proposed coating (cf. Figure 5), which made possible the reinforced superhydrophobic phenomena.

Figure 8 displays the dependence of the zinc dosage on the superhydrophobic phenomena. The increasing use of zinc did not persistently result in the increasing superhydrophobic properties but an initial increase and a subsequent decrease. There was an optimal dosage of zinc oxide with respect to the superhydrophobic phenomena. This outcome, as unmasked in Fig. 9, can be ascribed to the agglomeration of zinc oxide with an increasing dosage, which led to the superhydrophobic surface changed from the appropriate texture to the destructed texture. As such, a certain amount of zinc oxide is encouraged to use, so as to acquire the optimized superhydrophobic properties (such as 1.2 g in the present study).

Figure 6. The contact angles of the prepared coatings (a: N@PUC; b: Zn@PUC)

Figure 7. The rolling angles of the prepared coatings (a: N@PUC; b: Zn@PUC)

Figure 8. The contact angles of the prepared coatings with an increasing zinc dosage (from a to e with zinc oxide (g): 0, 0.6, 1.2, 1.8, 2.4)

Figure 9. The SEM imaging of the surfaces of the prepared coatings with an increasing zinc dosage (from a to e with zinc oxide (g): 0, 0.6, 1.2, 1.8, 2.4)

3.3. Ultraviolet resistance

Figure 10 displays the ultraviolet resistance of the prepared coatings. For the proposed coating, the superhydrophobic phenomena did not substantively change after the irradiation. By comparison, the increasing irradiation on the control coating resulted in a significant decrease in the contact angles. The incorporation of zinc into the proposed coating made a contribution to the increasing ultraviolet resistance which was essential for outdoor applications. In conjunction with the analysis and characterization (cf. Section 3.1), this may be due to the lower binding energy of electrons in zinc, which led to the inherent ultraviolet adsorption and thereby helped induce the ultraviolet resistance. This outcome may be further evidenced from the ultraviolet adsorption spectra (Fig. 11). The proposed zinc-mediated coating exhibited stronger ultraviolet adsorption in contrast to the zinc-free control coating. It is therefore clear that the incorporation of zinc into the proposed coating not only reinforced the superhydrophobic properties but also extra granted the proposed coating ultraviolet resistance.

Figure 10. The dependence of the contact angles on the irradiation time (254 nm)

Figure 11. The ultraviolet absorption properties from the prepared coatings

3.4. Abrasion resistance

The abrasion resistance of the prepared coatings was studied with the tape-peeling testing and the sandpaper friction. The increasing cycles of friction and stripping from the proposed coating did not lead to a substantive change in the superhydrophobic properties (Fig. 12 and Fig. 13). The increasing cycles of friction and stripping from the control coating resulted in a significant decrease in the contact angles. The incorporation of zinc into the proposed coating induced stronger wear resistance. In conjunction with Section 3.1 and Section 3.2, this may be due to the mediation of zinc oxide on the surface textures of the prepared coatings, in which zinc oxide itself as a transition-metal oxide possessed better wearing quality. In couple with the prominent wear resistance of the polyurethane layer, the proposed coating authenticated the sturdy ultraviolet and abrasion resistance.

Figure 12. The abrasion resistance from sandpaper friction testing

Figure 13. The abrasion resistance from tape-stripping testing

3.5. Anti-corrosion properties

The anti-corrosion properties of the prepared coatings were studied by immersing individually the coatings into hydrochloric acid and sodium hydroxide solutions and then taken out for testing. The increasing time for immersing the proposed coating did not lead to a substantial decrease in the superhydrophobic properties, regardless of the specified solution (Fig. 14 and Fig. 15). By comparison, the increasing time for immersing the control coating resulted in a substantial decrease in the contact angles. The incorporation of zinc into the proposed coating caused better anti-corrosion properties. In conjunction with the superhydrophobic phenomena (cf. Section 3.2), this may be attributed to the enforced superhydrophobic properties induced by zinc, which helped inhibit the contact of water to the surfaces and thus led to better anti-corrosion properties.

The anti-corrosion behavior of the prepared coatings was further analyzed and detected with the electrochemical impedance spectra (Fig. 16). The Nyquist curve of the proposed coating displayed a larger radius of capacitance in comparison to the counterpart of the control coating. This reveals that the proposed coating held larger resistance to charge transfer in comparison to the control coating. As such, the proposed coating showed the better anti-corrosion properties.

Figure 14. The resistance of the prepared coatings to hydrochloric acid corrosion

Figure 15. The resistance of the prepared coatings to sodium hydroxide corrosion

Figure 16. The electrochemical impedance spectra of the prepared coatings

3.6. Self-cleaning properties

The self-cleaning properties of the prepared coatings are displayed in Fig. 17, in which the coatings were smeared with coffee powder. The proposed coating left behind a clear surface when washed with 5 mL of water (cf. Case b). Under comparable conditions, the control coating left behind a few residues after undergoing the identical processes (cf. Case a). The proposed coating authenticated better self-cleaning behaviors in comparison to the control coating. This may be due to the enforced superhydrophobic properties, as explained, which made possible the better self-cleaning functions.

The self-cleaning properties were further checked by immersing the prepared coatings into a methylene-blue aqueous solution and then taken out (Fig. 18). The blue solution quickly rolled off the proposed coating and accordingly left behind a clear coating. By comparison, despite the pending time, the blue solution invariably left behind a few residues over the control coating. Once again, this outcome indicates that the proposed coating possessed better self-cleaning properties in comparison to the control coating.

Figure 17. The self-cleaning properties with coffee powder (a: N@PUC; b: Zn@PUC)

Figure 18. The self-cleaning properties with methylene-blue solution (a: N@PUC; b: Zn@PUC)

This study reported an exploratory work on developing a superhydrophobic coating capable of sturdy abrasion and weather resistance. Given the key factors in preparing superhydrophobic properties, such as the rough superhydrophobic surface and the weather resistance, this coating was developed with a zinc-mediated superhydrophobic surface in association with a polyurethane layer which possessed prominent wear resistance. The resulting coating unfolded the natural superhydrophobic phenomena with the superhydrophobic angle of up to 157.1°, greater or smaller by depending on the dosage of zinc. The incorporation of zinc into the proposed coating not only mediated the rough surface texture but also extra granted the ultraviolet resistance. In couple with the strong wear resistance of the substrate layer, the proposed superhydrophobic coating provided the expected sturdy abrasion and weather resistance. As such, the proposed coating shares a prospect with practical applications and especially outdoor applications. It is therefore authenticated that this work may serve as the exploratory foundation for developing superhydrophobic coating that might be suitable for potential applications. The future progress in this field will aid in facilitating the applications, particularly those that are used outside.

Author Contribution

Y.Q and Y.T performed the experiment, and M.Z and X. S helped guide the experiment and S. L wrote the mansucript.

Acknowledgement

not applicable

J. Chen, L. Yuan, C. Shi, C. Wu, Z. Long, H. Qiao, K. Wang, Q. Fan, ACS Appl. Mater. Inter. 13, 18142-18151 (2021)
K. Xu, S. Ren, J. Song, J. Liu, Z. Liu, J. Sun, S. Ling, Chem. Eng. J. 403, n126348 (2021)
C. Li, P. Wang, D. Zhang, Colloid Surface A. 624, n126835 (2021)
Y.A. Mehanna, E. Sadle, R. L.Upton, A.G. Kempchinsky, Y. Lu , C.R. Crick, Chem. Soc. Rev. 50, 6569-6612 (2021)
K. Liu, L. Jiang, Annu. Rev. Mater. Res. 42, 231-263 (2012)
L. Qin, Y. Chu, X. Zhou, Q. Pan, ACS Appl. Mater. Inter. 11, 29388-29395 (2019)
W. Barthlott, C. Neinhuis, Planta. 202, 1-8 (1997)
G.S. Watson, J.A. Watson, Appl. Surf. Sci. 235, 139-144 (2004)
G.S. Watson, B.W. Cribb, J. A. Watson, ACS Nano. 4, 129-136 (2010)
X. Gao, L. Jiang, Nature. 432, 36 (2004)
X. Li, K. Yang, Z. Yuan, S. Liu, J. Du, C. Li, S. Meng, Chem. Rec. 23, n202200298 (2023)
J. Tao, L. Dong, Y. Wu, X. Liu, J. Xie, H. Wu, Q. Ran, Composit. Part B. 273, n111245 (2024)
G. Qi, X. Liu , C. Li, C. Wang, Z. Yuan, Angew. Chem. Int. Ed. 58, 17406-17411 (2019)
X. Li, Y. Sun, Y. Xu, Z. Chao, Small. 14, n1801040 (2018)
H. Lim, D. Kwak, D. Lee, S. Lee, K. Cho, J. Am. Chem. Soc. 129, 4128-4129 (2007)
M. Zhang, T. Zhou, H. Li, Q. Liu, Appl. Surf. Sci. 623, n157085 (2023)
M. Jin, X. Feng, L. Feng, T. Sun, J. Zhai, T. Li, L. Jiang, Adv. Mater. 17, 1977-1981 (2005)
H. Zhao, W. Gao, Q. Li, M. Khan, G. Hu , Y. Liu, W. Wu, C. Huang, R. Li, Adv. Colloid Interface Sci. 303, n102644 (2022)
Z. Yuan, Y. Wu, J. Zeng, X. Li, K. Zang, H. Zhou, Environ. Sci. Pollut. Rep. 30, 52958-52968 (2023)
B. Zhao, R. Jia, Prog. Org. Coat. 135, 440-448 (2019)
C. Xie, C. Li, Y. Xie, Z. Cao, S. Li, J. Zhao, M. Wang, Surf. Interfaces. 22, n100833 (2021)

Scheme 1 is available in the Supplementary Files section.

No competing interests reported.

Scheme1.png
Scheme 1. Technical outline for fabricating the proposed superhydrophobic coating

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Journal Publication

published 17 Jun, 2024

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Editorial decision: Accepted
08 May, 2024
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08 May, 2024
Reviewers agreed at journal
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You are reading this latest preprint version

A Superhydrophobic Coating with Sturdy Abrasion and Weather Resistance

Status:

Journal Publication

Version 1

Abstract

Figures

1. Introduction

2. Experiment Section

2.1. Materials

2.2. Preparation of coating suspensions

2.3. Fabrication of superhydrophobic coatings

2.4. Analysis and characterization

2.5. Superhydrophobic angles

2.6. Ultraviolet resistance

2.7. Abrasion resistance

2.8. Anti-corrosion properties

2.9. Self-cleaning properties

3. Results and Discussion

3.1. Analysis and characterization

3.2. Superhydrophobic properties

3.3. Ultraviolet resistance

3.4. Abrasion resistance

3.5. Anti-corrosion properties

3.6. Self-cleaning properties

4. Conclusions

Declarations

Author Contribution

Acknowledgement

References

Scheme

Additional Declarations

Supplementary Files

Status:

Journal Publication

Version 1