Preparation And Properties Of Porous Polymeric Coatings With Superhydrophobicity Via Phase Separation

Inspired by the surface wettability of lotus leaves, red rose petals and shark skin, thefabrication and research of superhydrophobic surfaces has attracted considerable interest inrecent years. Superhydrophobic surfaces have great application value in oil-water separation,self-cleaning coatings, fluid drag reduction and other fields owing to their excellentnon-wetting to water or other liquids. However, there are still some key problems to solvebefore the superhydrophobic surfaces are widely used in our life. These problems include thepoor mechanical and thermal stability of the surface, complex process, high raw materialcosts and so on. Thus, it is necessary to develop a simple, low-cost and suitable for large-scaleproduction method to fabricate superhydrophobic surfaces with excellent stability.Thermally initiated free-radical polymerization was carried out directly on the glasssubstrate in the presence of co-porogens of1,4-butanediol (BDO) and cyclohexanol (CYA) or1,4-butanediol (BDO) and N-methyl-2-pyrrolidone (NMP), using butyl methacrylate (BMA)and ethylene dimethacrylate (EDMA) as main monomer, and2,2’-azobisisobutyronitrile(AIBN) as initiator. Porous polymeric coatings with the micro/nano roughness structure wereobtained via phase separation leaded by co-porogens during the polymerization process. Theinfluences of the reaction temperature, polymerization time, content of initiator and the massrate of two monomers on the properties of the coatings were discussed. Especially, the effectsof the content and polarity of the co-porogens on the microstructure and hydrophobicity of thecoatings were investigated. The hydrophobicity and microstructure of the polymeric coatingsurfaces were characterized and analyzed by contact angle (CA), scanning electronmicroscope (SEM) and atomic force microscopy (AFM). The stability of thesuperhydrophobic coatings was investigated by the non-wetting test, anti-chemicals andthermal treatment test, respectively.The polymeric superhydrophobic coating prepared with the co-porogens of1,4-butanediol (BDO) and cyclohexanol (CYA) shows a water contact angle (WCA) of153.8°and a low sliding angle (SA) of4.0°, when the reaction temperature andpolymerization time are75°C and20h, the mass fraction of AIBN is2%, the mass ratios ofmonomers to co-porogens, BMA to EDMA, and BDO to CYA are all50:50, respectively.SEM and AFM images of the superhydrophobic surface revealed its porous structure andmicro/nano roughness structure. Moreover, the superhydrophobic coating shows betterresistance to acid, alkali or salt. The polymeric superhydrophobic coating prepared with the co-porogens of1,4-butanediol (BDO) and N-methyl-2-pyrrolidone (NMP) shows a high WCA of159.5°anda low SA of3.1°, when the mass ratios of monomers to co-porogens, BMA to EDMA, andBDO to NMP are45:55,50:50,40:60, respectively. An increase of the polarity ofco-porogens can result in an increase of the average size of pores and polymericconglomerations. And94.10%of the percentage of gas-liquid contact area on the compositecontact surface was calculated by Cassie-Baxter model equation. Furthermore, thesuperhydrophobic coating has an excellent non-sticking property to the water droplet, goodchemical stability with better resistance to acid, alkali or salt aqueous solutions and thermalstability up to190°C.