| Pickering emulsion is a new kind of emulsion stabilized by solid particles instead of traditional organic surfactants. Compared with the traditional emulsion, Pickering emulsion has the advantages of strong interfacial stability, reduced bubbles, regeneration, low toxicity and low cost, and possesses wide applicable prospects in the fields of cosmetic, food, medicine, petroleum, and the waste water disposal. In this paper, Fe3O4 magnetic nanoparticles was introduced as emulsifier and stabilizer to construct the oil and water to prepare magnetic functional Pickering emulsion, and the influences of the surface modification and concentration of magnetic nanoparticles, oil polarity and volume ratio of oil to water on the stability, composition, type and microstructures of the resultant emulsions were investigated and the key technique to prepare the magnetic Pickering emulsion stabilized by Fe3O4 nanoparticles and the influence factors and controlled method for emulsion stability were summarized. We believe this research will be of important scientific significance and value for the design, preparation and investigations of functional Pickering emulsions besides magnetic Pickering emulsions and the investigations of the interfacial self-assembling of functional nanoparticles and the preparation technique of functional hollow spheres and nanocapsules.Firstly, a method was designed to characterize and analyze the contact angle of Fe3O4 nanoparticles at water-oil interface. The three phase contact angleθOW is the dominant factor for the stability and type of Pickering emulsions, but it is hard to determine theθOW of the brittle particles. The method designed here is that the common contact angleθO andθW (contact angle at air-oil interface and air-water interface) are measured by Washburn osmose method firstly, and then the three phase contact angleθOW can be calculated by the relationship ofθo,θw andθow deduced from Young'equation. Using this method, theθOW of Fe3O4 nanoparticles for four oils (nonpolar oil dodecane, weakly polar oil PDMS, strongly polar oil butyl butyrate and n-decanol) was investigated, and it was found that theθOW of Fe3O4 nanoparticles at dodecane-water interface is the most close to 90°while theθOW at butyl butyrate-water interface and decanol-water interface is much smaller than 90°. These results show that Fe3O4 nanoparticles tend to stabilize emulsions with oil of dodecane, but not for the emulsions with oils of butyl butyrate and decanol.In fact of the above results, the Fe3O4 nanoparticles were used as stabilizer to prepare Pickering emulsions with different oils, and the effects of particle concentration, oil polarity, and volume ratio of oil to water on the stability, composition, type and microstructures of the resultant emulsions were investigated. The results reveal that the Fe3O4 nanoparticles can stabilize dodecane/water and lOmPas-PDMS/water emulsions, but can not for emulsions with oils of butyl butyrate and decanol. After preparation, all the emulsions need certain period to be stable (about 511 minutes). With the increase of volume fraction of oil added, the stable emulsion fraction increases, the solid particle content in emulsion decreases, and the average droplet size of emulsion increases. The dispersion concentration of Fe3O4 nanoparticles has no obvious effects on the stability of emulsions, but the average droplet size of emulsion decreases when the particle concentration is greater than 0.75wt.%.In order to acquire Fe3O4 nanoparticles stabilized emulsions of strongly polar oil (butyl butyrate), the Fe3O4 nanoparticle surface was modified by the carboxyl acid (ethanoic, pentanoic, octanoic and decanoic acid) and silane coupling agent (RSi(OC2H5)3, R=CH3CH2-, (CH3)2CHCH2-, CH3(CH2)5-) to increase the hydrophobicity of particles, and the effects of particle surface modification on the stability, composition, type and microstructures of the resultant emulsions with both nonpolar oil (dodecane) and polar oil (butyl butyrate) were investigated. Silane coupling agent is a more effective modifier, because although the molar amount of silane coupling agent added is sixth that of carboxyl acid, the number of alkyl group on silane coupling agent coated Fe3O4 nanoparticles is higher than that on carboxyl acid coated particles. Monolayer coating of carboxyl acid and silane coupling agent on particle surface can undoubtly raise the hydrophobicity of Fe3O4 nanoparticles, and the lenghthening of alkyl chains in modifier and the increase of the coating percent of alkyl chains on particle surface can further increase the hydrophobicity of particles. Similar to Fe3O4 nanoparticles, the carboxyl acid coated Fe3O4 nanoparticles can not stabilize butyl butyrate-water emulsion, but can stabilized dodecane-water emulsion. However, when the alkyl chain in carboxyl acid is long (decanoic acid) and the content of alkyl group is high on the particle surface (the amount ratio of carboxyl acid to particle is 0.09mol/g added in synthesis), the stability of the dodecane-water emulsion is decreased with the decrease of the stable emulsion fraction. Greater stable emulsion fraction can be obtained for the dodecane-water emulsion stabilized by silane coupling agent coated Fe3O4 nanoparticles. Moreover, the silane coupling agent coated Fe3O4 nanoparticles can stabilize the butyl butyrate-water emulsion when the alkyl group in the modifier is (CH3)2CHCH2- and CH3(CH2)5-. The surface modification of Fe3O4 nanoparticles does not change the emulsion type, and all the emulsions are O/W in type. The modification of Fe3O4 nanoparticles has some influences on the composition and droplet size of the emulsions, but very weak.
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