Studies On Crystallization And Wettability Of Fluorinated Acrylate Copolymers Films

Due to properties of variety of colours, easy cut to required lengths, flectional, profiled or deep drawn, without damaging the organic coating, the prepainted coil has numerous applications in various industries, such as in the construction industry, the automotive and transport industries,etc. Films may suffer from all kinds of outdoor pollution as outside walls of building coatings in modern cities. It is extremely urgent to develop a kind of anti-graffiti and anti-fouling coil coating with the low surface energy because buildings cleaning is a challenge.?Fluorinated acrylate copolymers have become one of hot topics as anti-graffiti and anti-fouling coating due to their many special properties, including hydrophobicity and oleophobicity, chemical inertness, and thermal resistance, as well as excellent mechanical behavior. However, the fluorinated monomers are usually costly and the excellent surface performance of fluorinated acrylate copolymer may be lost when exposed in polar environment induced by surface reconstruction, it is challenging to fabricate excellent surface performance of hydrophobicity and oleophobicity with lower fluorine content. In this paper, fluorinated acrylate copolymer was synthesized and SiO₂/polyacryalte composite coating was prepared before further curing with HDI-trimer. Composite coating has good surper hydrophobicity and oleophobicity. The main research contents are listed as follows:First of all, a series of fluorinated acrylate copolymers by using monomers of 2-perfluorooctyl ethyl acrylate （FOEMA） and various lengths of side chains of n-alkyl acrylates （AAs） （n= 4, 8, 12, 16, 18） were synthesized by free radical polymerization in solvent of xylene and initiator of BPO. The copolymer chemical composition and crystallization were analyzed via Fourier Transform Infrared Spectroscopy （FTIR）, Nuclear magnetic resonance spectrum（¹HNMR）, gel permeation chromatography （GPC）, X-ray Diffraction（XRD）, Polarizing Optical Microscope（POM） and Differential Scanning Calorimetry （DSC） etc. The results suggest that crystallization of fluorinated acrylate copolymers closely related to the side-chain length of hydrocarbon. When n numbers of C_nH_2n+1 were 16 and 18, the hydrocarbon side-chain of the copolymers crystallized at room temperature, while the copolymers with n of 4, 8 and 12 might not crystallize and was in the rubbery state at the same condition. The crystalline structure is determined by the copolymer composition: when the content of the fluorinated monomer is low, the copolymer is mainly crystallized with side chains of hydrocarbon chains; when the content of the fluorinated monomer is high, the copolymer is mainly crystallized with perfluoroalkyl side-chain.Secondly, molecular dynamics simulation was used to simulate X-ray Diffraction of fluorinated acrylate copolymers by Forcite module under COMPASS force field. The effect of different length of hydrocarbon side-chain on crystallization of fluorinated acrylate copolymers was studied. Simulation results were consistent with experiment date.Thirdly, surface wetting properties of fluorinated acrylate copolymers with different length of hydrocarbon side-chain were investigated and the effect of crystallization of fluorinated acrylate copolymers on surface wetting properties of films was discussed. In addition, surface composition and topography of copolymers were analysed. The results suggest that the crystallization of hydrocarbon side-chain can promote perfluoroalkyl side-chain to migrate to the polymer–air interface. Compared with amorphous copolymer, the enrichment of fluorine on surface of crystalline copolymers film is higher, and hydrophobicity and oleophobicity on those surface is better. Phase separation is observed obviously on crystalline copolymers film, moreover, it lead to a great increase in roughness and hence improve hydrophobicity. Preparation of crystalline copolymers through choosing a suitable acrylate monomer is an available way to get good hydrophobic and oleophobic copolymer film under the condition of low dosage of fluorinated monomer.Furthermore, thermosetting resin is synthetized by using monomers of stearyl acrylate, fluorinated monomer and hydroxyethyl methacrylate. The influence of hydroxylic monomer dosage and film formation condition on surface wetting and mechanical properties were investigated. XRD and DSC results indicated that the crystallinity of thermosetting copolymer is bigger than that of thermoplastic copolymer and the molecular arrangement is more orderly. XPS and AFM shows the fluorine of thermosetting copolymer prefer to enrich on the film suface, for perfluoroalkyl side-chain of thermosetting copolymers can be fixed on the surface by the cross-linked structure, which limitied molecular migration and rearrangement. Therefore it has better hydrophobicity and oleophobicity and surface stability.Finally, SiO₂/polyfluoroacrylate composite coating were prepared by directly blending nano-silica particles into fluorinated acrylate copolymer and further cured with HDI-trimer. The effects of silica dosage and concentration of coating solution on the wettability of composite coating were studied. The results suggest that the silica dosage and concentration of coating solution have important influence on the roughness of the composite coating. The composite coating has best hydrophobicity and oleophobicity when the silica dosage is 20% and the concentration of coating solution is 10%. Anti-graffiti, anti-fouling and mechanical properties of the composite coating were tested to be better than those of some commercial products with modified silicone and polyurethanes coating.