Synthesis Of Fluorine-containing Polyacrylate Latex And Multiscale Coupling Model Of Water-endurance For Waterborne Coating

Abstract Fluoropolymer has been widely used in the fields of coatings, spinning and leather for their excellent weather resistance, anticorrosive ability and solvent resistance. The synthesis of fluoropolymers and the relation between the molecular structures and its properties have always received much attention. Thus the study on the preparation method and their properties of fluoropolymer is very interesting. With the establishment of environmental law, it is necessary to look for green technologies for the preparation of fluoropolymer. Emulsion polymerization is one of the most important methods to prepare the fluoropolymer with excellent and environmental properties. There are many advantages for above synthesis method, such as, easy thermolysis, high molecular wight, high reaction speed, easily control and its emulsion used straightly. In the section of synthesis of the thesis, the studies are on the preparation of fluoropolymer with their controlled latex structure by emulsion polymerization method.From the view of dimension, multiscale includes microscopic, mesoscopic, macroscale. Microscopic scale is on the level of atom, molecular for the material. Moleular simulation is used to simulate molecular structure and behavior at the level of atom model, and to obtain a variety of physical and chemical properties for the material. This can help the design of new materials, and shorten the period of development of new material, and recuce the development cost. However, the studies on structures and behavior of polymer in complex emulsion system by molecular simulation have exceed the ability of computer because several thousands atoms would spend much computational time. These must be done by another larger scale simulation method, namely, mesocsopic simulation. Dissipative particle dynamics (DPD) as one of mesocsopic method is used widely, which represents hydrodynamics interaction force over larger length and times scales. Thus it can be suitable for the study on the existence behavior of surfactants and the interaction with polymer in aqueous solution. Macroscopic scale is mainly carried out by the combination statistics and experiments. Though many relative mature theory and simulation methods have been put forward on every scale, no mature connect method has been found to couple these different scales. At present, the couple method between different scales is scare. And the scientific question of coupling multiscale from unimolecular design to material processing is one of forward looking and defiant magnitude project. Also it is one crossed and new subject growing point related to polymer science, condensed state, and material science and numerical mathematic.In our thesis, polyacrylate film as a binder is the investigated subject. During the period of the formation of polyacrylate film, many phenomena have been involved, such as, molecular aggregation, latex particles, diffusion and particle motion, which exhibits the change on microscopic, mesoscopic and macroscopic scales, respectively. Thus, multiscale coupling model method is used to predict or conclude the rules and properties on higer scale by use of rule and properties on lower scale. Then we can explore the coupling model from microscopic structure to continuous medium, and predict or optimize the physical and chemical properties of water-borne coating. This work is very meaning for the theoretic and experimental study of new functional coating and the development the theory of coating study.In second chapter, PTFE modified polyacrylate latex has been synthesized. PTFE can improve the weatherability and self-cleaning properties of water-borne polyacrylate coating. PTFE modified polyacrylate is prepared by the copolymerization of acrylate monomers in aqueous medium composed of ionic, nonionic, fluorine-carbon surfacetant, and the swollen particles of PTFE. Through the study of synthesis technology, the optimized reaction conditions such as monomers ratio, composite surfactant component, and reaction temperature, the content of PTFE has been confirmed. The morphology of the latex particles with about 180 nm are observed by scanning electron microscopy (SEM). The heatstability and water-endurance of modified polyacrylate is improved obviously. This method of pre-emulsified PTFE modified polyacrylate has improved the compatibility between polyacrylate and PTFE. F1S content of the surface of the latex film is 8.99%. Through analysis of the surface chemistry content by XPS, it has proved that PTFE has a trend of moving outside of the film layer for its low surface energy when the latex film forms.In third chapter, one method to produce interpenetrating polymer network (IPN) core-shell fluorine-containing polyacrylate latex has been presented. It has been prepared by seed emulsion polymerization of fluorine-containing acrylate monomers and acrylate monomers in an aquaeous medium composed of mixed emulsifiers. The chemical composition and core-shell structure are characterized by FTIR spectrometry and TEM. The cross-linking reagent has made polyacrylate interpenetrate with each other, which can improve the physical properties of latex film. IPN structure of latex particle has been indicated by the improved ability of organic reagent endurance and thermal stability comparing with uncrossing core-shell structure. Meanwhile, the surface analysis of the latex film by XPS reveals that a gradient concentration of fluorine exists in the structure of the latex film from the film-air interface to the film-glass interface. This synthesis method has proved that fluorine-containing latex with excellent properties can be prepared by controlling the content of fluorine monomer on the shell and crosslink reagent.In fourth chapter, dissipative particle dynamics (DPD) has been used to predict the phase behavior and microstructure of Cetyltrimethylammonium bromide (CTAB)/octane/1-butanol/water system. Firstly, the simulated objects have been supposed as the coarse particle (DPD bead). Suitable method has been selected to calculate the interaction between particles. By analyzing the simulated interface tension and microstructure, their phase diagram of microemulsion has been fabricated, which is consitent with experimental result. DPD method has been also used to investage the interaction between flurorine carbon surfactant (FC6201) and PTFE. One characteristic parameter of FC6201 surfactant, 13mmol/L of critical micelle concentration (CMC), has been obtained. Combined the aggregation of PTFE and FC6201 and the change of mean square end-to-end distance of PTFE, the interaction between PTFE and FC6201 has been discussed with the increase of FC6201 concentration. The results show that PTFE can be swollen well only if the concentration of FC6201 is above one value, and this benefit the polymerization of other organic monomer around PTFE molecule or in the interspace between PTFE molecules, which can offer the theoretic reference for the synthesis of PTFE modified polyacrylate in second chapter.In fifth chapter, the surfact tension of polyacrylate has been calculated by MD, and compared with experimental critical surface tension. It has proved that MD method can calculate the surface tension of polymer, which can not be obtained directly from experimtal method. Meanwhile, surface tension of polyacrylate with different curing degree, the content of styrene and acrylic has also been calculated by MD. The ideal curing degree, 86% has been confirmed by experiment. One mathematical model predicting the surface tension of polyacrylate is built by coupling the effect factors on surface tension with statistical method. This model would be used for the mutiscale modeling of water-endurance of polyacrylate in seventh chapter.In sixth chapter, molecular dynamics simulations have been applied to investigate the diffusion behavior of water molecules inside of amorphous polyacrylate. The results showed that the simulated diffusion coefficients and activation energies are similar to those of experiments. The activation energy to desorb bound water is higher than that of free water in polyacrylate film, and their difference value is close to the hydrogen-bonding energy between water and polyacrylate. According to the simulation result, it has been concluded that bound molecules move from one polar group of polyacrylate to another, and this is followed by occasional jumps. The diffusion coefficients of water molecules have been calculated by MD simulation under the content of acrylic, stryrene, and the curing degree has been built, and its accuracy has been examined. This can help us understand the interaction mechanism between water mocule and polyacrylate at the level of molecule, and obtain the diffusion coefficients of water molecule in polyacrylate system. These data can be used for the modeling mutilscale of water-endurance of polyacrylate in seventh chapter.In the last chapter, the effect of the content of acrylic and styrene on the adsorption ratio of polyacrylate film has been determined by experiment. It has been revealed that the adsorption ratio of film increase gradually with the increase of acrylic content, while it decrease gradually with the increase of stryrene. The experimental result of adsorption water reveals that the increase of curing degree would result in the decrease of ratio of adsorption water. Thus the effect factors on the ratio of water absorption of polyacrylate film include water-borne functionality, curing degree, diffusion coefficient of water molecules. By the statistical method, the multiscale model can be built as follows. g (φ, D, C_r)=0.802 + 21.02φ+ 0.24D + 0.84C_r - 15.38φC_r - 0.18C_rD Hereinφis water-borne functionality. D is the diffusion coefficient. C r is curing degree. g (θ, D , Cr)(%) is the ratio of water adsorption. The biggest error predicted by above equation is 7.53%. Thus the model can be used to investigate the water-endurance ability of the film quantificationally.In this thesis, multiscale method is firstly used in analyzing the water-endurance ability of coating binder. By using the statistical method, the molecular mechanics, molecular dynamics and experiments have been coupled and used to build the multiscale model predicting the physical properties of complex system. This model can be considered as the submodel of multiscale model for the water-endurance ability of water-brone coatings. Meanwhile, the method of building model can provide an idea for building the multiscale in next step. Meanwhile, it has been proved that the physical and chemical properties of complex fluid can be analyzed and predicted by multiscale method.