Elsevier

Chemical Engineering Journal

Volume 369, 1 August 2019, Pages 1-7
Chemical Engineering Journal

Fabrication of robust and repairable superhydrophobic coatings by an immersion method

https://doi.org/10.1016/j.cej.2019.03.021Get rights and content

Highlights

  • A novel kind of superhydrophobic coating was successfully fabricated with a simple two-immersion method.

  • The coating exhibits excellent robustness under mechanical abrasion or impact damage.

  • The coating has a repairable ability via simply immersed again.

  • The superhydrophobic coating is expected to be used on the inner surface of irregular structures.

Abstract

The development and practical application of superhydrophobic coatings are mainly limited by complex fabrication processes and fragile surface structures. Meanwhile, it is difficult to overlay superhydrophobic coatings on the internal surfaces of special shaped constructions. To handle these problems, the simple two-immersion method was adopted and a kind of novel repairable superhydrophobic surface was successfully fabricated with the mixture of fluorocarbon resin and nanometer silicon dioxide. The technological parameters were discussed and a serious of robustness tests were carried out on the optimized coating. The results indicated that the surface maintained superhydrophobic after 1600 cm sandpaper abrasion and still repelled water after 20,000 cm abrasion. Also, water and sand impact tests were put into effect to prove this coating can endure harsher environment. Through further investigation, it was found that this coating had a repairable ability against mechanical damage via simply immersed again. In addition, the coating exhibited ideal properties at different pH levels. As the porous foam test revealed, this superhydrophobic coating is expected to be used on the inner surface of irregular structures.

Introduction

Since the discovery of lotus effect, superhydrophobic surfaces with static water contact angle more than 150° and sliding angle less than 10° have shown distinguished performance in different potential application fields, such as self-cleaning, oil-water separation, anti-condensation, anti-frosting, anti-icing and anti-corrosion [1], [2], [3], [4], [5], [6], [7], [8], [9], [10], [11], [12], [13], [14]. As we know, the formation of superhydrophobicity is attributed to highly textured structures and low surface energy. However, the superhydrophobic property and surface robustness are inherent contradictions because with the increase of roughness, the hydrophobicity enhances while the surface becomes more vulnerable [15], [16], [17], [18], [19].

Techniques used to solve the robustness and durability issues mainly include adjusting the coarse structure, strengthening the bonding between superhydrophobic coatings and substrates and making the surface self-healing. Originally, it is demonstrated that microscale bumps can provide protection to nanoscale roughness, which is too fragile to resist destruction, so the micro/nano hierarchical structure is essential to enhance the wear resistance [20], [21], [22]. With the further research, it is found that this composite structure is still vulnerable and the coating is far from meeting the requirement of robustness. During the past few years, adhesives have been widely used to splice the films and substrates to prevent the rough structure from being polished with external force [23], [24], [25], [26], [27], [28]. Although this method has good effect on improving robustness, it usually takes two steps to complete the preparation and needs complex techniques. Also, the coating is customarily painted by brushing or spraying method, which cannot be applied to inner wall or other complicated parts’ surfaces, unlike immersion or dipping method [29], [30]. In addition, to imitate lotus leaves, which have the ability to regenerate epicuticular wax to maintain the surface low energy after damage or contamination, self-repairable surfaces have been created successfully in two dimensions, keeping the existence of rough structures or ensuring the continuous supply of low energy substances [31], [32], [33], [34].

As inspired by the above works, we fabricated a novel mechanically robust superhydrophobic surface with repairing ability through straightforward immersion method. A kind of hydrophobic resin, which has strong bonding with substrate and can fully cure at room temperature, and superhydrophobic nanoscale silica particles were major components of the coating and the particle content and immersion time were discussed seriously to ensure achieving optimized performances. Sandpaper abrasion and sand/water impact tests all demonstrated that the coating could withstand a considerable degree of external force destruction. What’s more, this coating was able to return to superhydrophobic state via immersed again after suffering mechanical damage, which mainly because of the recovery of micro/nano hierarchical structure. In practical, the obtained superhydrophobic coating is applicable to a modest environment and it is believed that it can be prepared in large scale application, even on the inner surfaces of complex structural parts.

Section snippets

Materials

Fluoroethylene vinyl ether (FEVE) and curing agent were purchased from Suzhou CY-CH Co., Ltd. Silica nanoparticles with the size of 10–20 nm were obtained from Evonik Degussa China Co., Ltd. 1H, 1H, 2H, 2H-perfluorodecyltriethoxysilane (PFDTES) were provided by Sikang New Material Co., Ltd. Absolute ethyl alcohol (EtOH), acetone, ammonium hydroxide (28%), deionized water, tetraethyl orthosilicate (TEOS), butyl acetate, hydrochloric acid (HCl) and sodium hydroxide (NaOH) were purchased from

Effects of particle content and immersion time on wettability

Fig. 1 shows the sketchy procedure to fabricate superhydrophobic coating via two-step immersion method. First, superhydrophobic silica nanoparticles and FEVE resin, a kind of fluorocarbon hydrophobic resin, are added to butyl acetate. Resin and particles dispersed evenly in the diluent by magnetic agitation for about 15 min. Then, the glass substrate was immersed into the solution for 5 min. At this first-immersion process, the coating was painted firmly because of the cohesive action between

Conclusions

In conclusion, a new kind of superhydrophobic surface has been developed via extremely simple two step immersion method with fluorocarbon resin and silica particles. The immersion time and particle content have both been discussed and the contact and sliding angles of the surface are 159.5° and 1.0°, respectively, with 30 min second-immersion time and 25% nanoparticle content. Through abrasion and impact tests, the robustness of superhydrophobicity is systematically demonstrated. It is worth

Notes

The authors declare no competing financial interest.

Acknowledgments

This work was financially supported by the National Natural Science Foundation of China (Grants 51671055, 51676033), the China National Key R&D Program (2016YFC0700304).

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