Preparation And Applications Of Hydrophobic And Superhydrophobic Composite Materials Base On Nano-SiO₂and Acrylate Polymers

In recent years, hydrophobic and superhydrophobic materials have attracted much attention due to their wide range of practical value. Since the "lotus effect" was revealed to closely relate to multiscale roughness structures and waxy substance with low surface energy on the surface of lotus leaves, a large number of methods have developed to prepare hydrophobic and superhydrophobic materials from these two aspects. Many methods have some drawbacks, e.g., require special equipment, complicated preparation steps, high cost and not suitable to fabricate large size coating and so on. In addition, superhydrophobic coatings have a widespread problem of poor mechanical strength, limiting their practical application. In order to solve the above problems, two methods were used to prepare hydrophobic and superhydrophobic coatings in this research, organic-inorganic hybrid method and phase separation method. It is easy to fabricate large area hydrophobic and superhydrophobic coatings without special equipment through these two methods. Pencil hardness and adhesion were used to characterize practical value of superhydrophobic coatings. In this research, superhydrophobic coatings with practical value were prepared by us, and we also developed two aspects of the applications of hydrophobic and superhydrophobic materials, oil-water separation and delay icing. Research was divided into five parts in this paper:(1) The acrylate polymer and fluorinated acrylate polymer were prepared through solution polymerization. The hydrophobic and superhydrophobic coatings were fabricated by adding nano-SiO2particles to the above two acrylate polymer solutions, respectively. Blending SiO2sol (methanol) and acrylate polymer, the hydrophobic composite coating was obtained with water contact angle (WCA) of121.6°when the weight ratio of SiO2(sol) to copolymers reached to0.8. To reduce the surface energy of the coating, the fluorinated acrylate polymer was prepared by introducing dodecafluoroheptyl methacrylate (DFMA) to the polymerization system at the beginning of the reaction. When the weight ratio of SiO2(sol) to copolymers was0.8, the strong hydrophobic composite coating with WCA of142°was got by mixing SiO2(sol) in methanol and the fluorinated acrylate polymer. The superhydrophobic composite coating with strong self-cleaning capacity was obtained by mixing two kinds nano-SiO2of SiO2(sol) in methanol and SiO2(sol) in isopropyl alcohol and the fluorinated acrylate polymer. The superhydrophobic composite coating with WCA of156.2°and CAH (contact angle hysteresis) of2.4°was fabricated when the weight ratio of total SiO2to copolymers was0.5and the weight of hydrophilic silica was70%of the weight of total SiO2. The hydrophobic, strong hydrophobic and superhydrophobic composite coatings which prepared by organic-inorganic hybrid method based on nano-SiO2and acrylate polymers have good practical value for high thermal stability, very good adhesion with the substrate and suitable for the preparation of large area coating.(2) The polystyrene-polymethyl methacrylate (PS-PMMA) random copolymer was prepared through suspension polymerization. The superhydrophobic coatings of the PS-PMMA random copolymer were fabricated by phase separation method with the induction by ethanol (nonsolvent). When the ethanol content was50%(v/v) in the random copolymer solution, the superhydrophobic coating of the PS-PMMA random copolymer with WCA of157.8°and CAH of6.8°was prepared. The random copolymer coatings had good acid and alkaline stability and could be used in acid and alkaline environment. On the occasions of less demanding hardness of coatings, the PC board coated with the superhydrophobic random copolymer coating still has practical value. Furthermore, the superhydrophobic SiO2/copolymer composite coatings with strong hydrophobicity and self-cleaning capacity were prepared by adding SiO2(sol) in isopropyl alcohol to the random copolymer solution (ethanol content,50%). The superhydrophobic SiO2/copolymer composite coating with WCA of162.3°and CAH of1.7°was fabricated when the weight ratio of SiO2to random copolymer reached to30%.(3) The PS-PMMA block copolymer was prepared through anionic polymerization. The superhydrophobic coatings of the PS-PMMA block copolymer were fabricated by phase separation method with the induction by ethanol (nonsolvent). When the ethanol content was60%(v/v) in the block copolymer solution, the superhydrophobic coating of the PS-PMMA block copolymer with WCA of156.7°and CAH of7.1°was prepared. The block copolymer coatings also had good acid and alkaline stability. It was found that the PS-PMMA block copolymer could improve the adhesion between the coating and the substrate compared with the PS-PMMA random copolymer. On the occasions of less demanding hardness of coatings, the PMMA, PVC and PC boards coated with the superhydrophobic block copolymer coatings still have practical value. Moreover, the superhydrophobic SiO2/copolymer composite coatings with strong hydrophobicity and self-cleaning capacity were prepared by adding SiO2(sol) in isopropyl alcohol to the block copolymer solution (ethanol content,60%). The superhydrophobic SiO2/copolymer composite coating with WCA of168°and CAH of1.2°was fabricated when the weight ratio of SiO2to block copolymer reached to20%.(4) The hydrophobic composite membranes fabricated by mixing SiO2(sol) in isopropyl alcohol and the fluorinated acrylate polymer were used to separate toluene and water in pervaporation. The composite membranes showed very strong mechanical strength to withstand a certain pressure, good water resistance and high thermal stability. The chemical composition and physical structure of the fluorinated acrylate polymer membrane would be changed by adding hydrophobic nano-SiO2particles to the fluorinated acrylate polymer. The microporous structures in the body of the composite membranes were fabricated by the aggregated silica in the membranes forming process. Incorporation of the silica fillers into the fluorinated acrylate copolymer membrane could greatly improve toluene flux, but decrease separation factor. The influences of operating conditions (downstream pressure and feed temperature) on separation factor and permeate fluxes (toluene and water) were investigated. These composite membranes could quickly and efficiently process large amounts of wastewaters by hydrophobic pervaporation. After calculation, the composite membranes with very strong sewage treatment capacity in this study have practical value in sewage treatment.(5) The strong hydrophobic composite coating of SiO2/the fluorinated acrylate polymer and the superhydrophobic coating of the PS-PMMA random copolymer were applied to the research of delay icing. Experimental results showed that the coatings with strong hydrophobicity and superhydrophobicity in this paper had good effect of delay icing.