Preparation and investigation of waterborne fluorinated polyacrylate/silica nanocomposite coatings
Graphical abstract
“Currunt-bun like” PFA/SiO2 nanocomposite particles confer rough surface of the film. Due to the amount and dispersion condition of silica in PFA film, surface roughness and fluorine content at the film surface can be varied.
Introduction
Organic/inorganic nanocomposite particles are of growing interest to researchers in past decades [1], [2], [3], [4], [5], [6], [7]. There are numerous applications of these nanocomposite materials, such as outdoor façade coatings [8], [9], [10], synthetic mimics for cosmic dust [11] and photonic devices [12]. Among inorganic nanoparticles, silica is the most widely investigated and has many applications in industrial fields. For example, copolymer/silica nanocomposite particles have been manufactured to produce exterior façade coatings [13]. Polymer/silica nanocomposite particles can be simply prepared by heterofluocculation between silica sol and polymer latex [14]. However, this kind of nanoparticles have been proved to exhibit inferior silica adhesion property [14], [15] and low transparency after film formation [16]. A lot of research have been focused on in situ co-polymerization of vinyl monomers in the presence of silica in alcohol/water mixtures [17], [18], aqueous solution [19], [20], [21] and alcoholic system [22], [23], [24] to produce film-forming polymer/silica nanocomposites. A convenient route to prepare nanocomposite particles includes polymerization of vinyl monomers in the presence of silica sol (in situ) via aqueous emulsion polymerization. Chen et al. [20], [21] synthesized PMMA/SiO2 hybrid particles with PMMA as core and silica particles as shell by using an auxiliary monomer of 2-(methacryloyl) ethyltrimethylammonium chloride or 1-vinylimidazole to stabilize hybrid microspheres and proposed a formation mechanism of the raspberry-like hybrid microspheres. They pointed out that the strong acid–base interaction between hydroxyl groups of silica surfaces and amino groups was strong enough for promoting the formation of long-stable PMMA/SiO2 hybrid particles. Zhang et al. [25], [26] have synthesized PS/SiO2 by miniemulsion polymerization in the presence of 3-methacryloxypropyltrimethoxysilane (MPS) modified silica nanoparticles and obtained core–shell morphology nanocomposite particles. The amount of MPS grafted on the silica surface was 8.7 molecules/nm2 and 10.8 molecules/nm2 for 45 nm and 108 nm silica, respectively. It has been reported that there are about 7 Si-OH/nm2 for Stöber silica [27], therefore, the results obtained by Zhang et al. confirmed multiple layers of MPS on silica surface. Qi et al. [28] prepared acrylate polymer/silica nanoparticles via miniemulsion polymerization. They found that MPS modified silica particles exhibited a good dispersion ability in the polymer matrix, and this kind of nanocomposite latex particles are suitable for coatings or impact modifier for plastics.
Previous literatures are mainly focused on morphology of polymer/silica nanocomposite particles, however, only a few works were concentrated on fabrication of film forming properties and investigation of surface compositions of the nanocomposite films [5], [16], [29], which will have significant meaning for commercial applications. Fluorinated polyacrylate has good film-forming behavior, low surface energy and thermal stability, therefore, by combining advantages of fluorinated component with silica nanoparticles, it is assumed to obtain novel and special properties of such kind of nanocomposites.
In this work, the synthesis of fluorinated polyacrylate/silica nanocomposite particles and film properties is reported. Thus, a series of fluorinated polyacrylate/silica particles were prepared by in situ miniemulsion polymerization in the presence of varying proportions of silica. Correlations of surface microstructure, chemical composition and silica content with the nanocomposite film properties were investigated.
Section snippets
Materials
Methyl methacrylate (MMA), butyl acrylate (BA) and tetraethoxysilane (TEOS) were obtained from Xilong Chemical Co., Ltd (Guangzhou, China). Inhibitor in MMA and BA was eliminated by passing neutral alumina. 1H,1H,2H,2H-heptadecafluorodecyl methacrylate (FA) monomer was prepared in our lab. 3-methacryloxypropyltrimethoxysilane (MPS) was bought from Nanjing Xiangqian Chemical Co., Ltd. The initiator of ammonium persulfate (APS) was obtained from Tianjin Bodi Chemical Co., Ltd and recrystalized
FT-IR and 19F NMR analyses of PFA/SiO2 nanocomposite films
FT-IR spectra of silica are shown in Fig. 1. It is shown in Fig. 1b, that the peak at 1075 cm−1 is ascribed to stretching vibration of SiOSi. The absorption at 944 cm−1 is assigned to SiOH, and stretching vibration of SiO occurs at 793 cm−1 and 572 cm−1. It is seen that the peak of CO at 1703 cm−1 appears in the spectrum of modified silica, demonstrating that MPS was grafted onto surface of silica.
An important question is how much MPS is required to cover the surface of the particles [31].
Conclusions
Copolymerizing acrylic monomers of MMA and BA with 1H,1H,2H,2H-heptadecafluorodecyl methacrylate (FA) in the presence of MPS-functionalized silica can obtain nanocomposite particles with “currunt-bun like” morphology. Drying aqueous nanocomposite dispersions leads to films with high transparency. The transparency of such films decreases from 93% to 88% with increasing amount of silica from 0 g to 0.15 g, as judged by visible light transmittance spectroscopy. The films showed improved surface
Acknowledgment
This work is financially supported by National Natural Science Foundation of China (Grant No. 51173006).
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2020, Progress in Organic CoatingsCitation Excerpt :Besides the improvement in common properties, superhydrophobic surface has also been designed [21]. In general, two main concepts are used, one is to create a microscale or nanoscale rough structure on film surface that is able to provide a high water contact angle (CA) [22], and the other is to decorate the nano-SiO2 with fluorocarbon polymers to reduce surface energy [6,14,23], or even with both approaches used together to obtain a satisfying hydrophobicity [11,14,24]. For instance, fluoroalkyl silane modified nano-SiO2 particles [23], silica-fluoropolymer hybrid nanoparticles [24] and nanoparticles blended with fluoropolymer [25] have all been used to form a superhydrophobic coating surface.