Translated Abstract
Superhydropbobic (SH) coating with a high water contact angle and a low water roll-off angle can make water droplets rolling off easily from its surface, simultaneously removing the dust or contamination, which endows attractive self-cleaning function to the coatings. SH coatings possess broad application potentials in fields such as anti-fouling, anti-icing, anti-fogging and corrosion protection. However, the present reported SH coatings usually have disadvantages like poor abrasive resistance, low adhesion and can＇t retain long-life SH property, which seriously hamper their practicality. Bearing good abrasive resistance, flexibility and strong adhesion, acrylic polyurethane (APU) has been widely used as coatings or paints for automobiles, architectures and decorations. Silica nanoparticles are usually employed to construct micro- and nanometer scale roughness required for SH coatings, due to their easy preparation, adjustable diameters and good abrasive resistance. Therefore, it is supposed that combination of APU and silica NPs will be effective to acquire SH coatings with excellent mechanical durability. Nevetheless, improvement of the abrasive resistance and adhesion still remain as challenges when preparing coatings with outstanding SH property.
In this dissertation, the chemical composition and roughness of the APU cotaing surface were adjusted by introducing low surface energy additives and hydrophobic modified silica NPs into bi-component APU resin matrix, respectivly. With this effort, hydrophobic and superhydrophobic coatings were facilely obtained while maintaining the good mechanical properties of the APU resin matrix. The following results were obtained:
1) A hydrophobic APU coating was obtained by facile mixing fluorine-containing resin or silicon/fluorine containing additives as low surface energy components with bi-component APU as the film-forming resin. During the curing process, most of the low surface energy components migrate to the top layer of the coating, whereas the matrix resin in the bottom layers attached stably to substrate. This character makes it possible that a significant increase of water contact angle (from 84° to 108°) was achieved by introducing a small percentage (0.5%) of the low surface energy. Besides good adhesion and weather resistance, this kind of APU coating can exhibit excellent abrasive resistance, which displays a water contact angle of ＞105° even with 20% loss of its thickness due to abrasion. The composition and structures of additives which can significantly increase the CA of APU coating have been analysis. The results showed that it is probably due to a Si-O-Si structure in their backbone and alkyl groups in their side chains, additive No. 1 can easily migrate to the top layer of the coating based on their low density and low melt point. The preparation method of this hydrophobic APU layer is facile to carry out with the commercial raw materials, which is applicative for large-scale industrial manufacture.
2) SH silica NPs were prepared through a one-pot sol-gel process and a two-step synthetic process based on the modified st?ber method. Both of these two kinds of silica NPs can construct micro- and nanometer scale roughness structures which exhibit a typical lotus effect. It was found that the hydrophobic performance of the silica NPs highly depended on their size and morphology, the ones with diameters around 400 nm showed outstanding SH property. In comparsion with the modified St?ber method which has a relative low yield as well as a much longer production period, the one-pot method is more efficient for preparation of silica NPs in a large scale and obtaining superhydrophobic APU coating based these silica NPs.
3) A SH APU coating with good adhesion and abrasive resistence was prepared by introducing hydrophobic silica NPs into acrylic resin, spraying and curing with isocyanate. The silica NPs modified with fluoroalkyl constructed hierarchical micro- and nanometer scale on the surface of the APU layer and was anchored into the APU substrate through interaction between the silicon-hydroxy groups and isocyanate groups. This dual characters ensured the APU layer a static water contact angle (CA) of ＞160°, a sliding angle of ~ 10°, good abrasive resistance and adhesion (zero level). The facile spray film-forming method as well as a mild room temperature curing process make this kind of SH layer suitable for protection or modification of large-scale parts, providing a novel pathway to development of high performance, self-cleaning SH surface.
The academic interests of this dissertation can be elucidated from both of the theoretical and practical aspects, on one hand, it has been realized that additives with flexible Si-O-Si backbone as well as hydrohobic alkayl gropus are very effective to improve the hydrophobic property of an organic coating; on ther other hand, by combination of resin matrix with excellent film-forming property and SH silica NPs, a SH APU layer with outstanding mechanical durability was prepared through a facile sprying method. This opens a way for large-scale preparation of SH layers and accelerates the practicality of the SH coatings.
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