Study On Synthesis And Properties Of Pickering Emulsions Stabilized By Two Components Of Nano Silica And Nano Titania

The traditional emulsion is formed by adding emulsifiers to overcome the instability caused by the area of oil/water interface.However,in general,the traditional emulsifiers are toxic and can contaminate the environment.Pickering emulsion is a kind of emulsion which can be stabilized by solid particles with emulsifying ability in stead of conventional emulsifiers.Pickering emulsion has the strong stability in thermodynamics,and its discovery has greatly reduced the use of emulsifiers,so this kind of environmentally friendly emulsion has been valued and researched by scholars.The solid particles which replace emulsifiers can be inorganic nanoparticles,organic particles and amphiphilic Janus particles.In contrast,inorganic nanoparticles are easy to prepare,and it is widely used in the fields of catalysis,biomedicine,cosmetics and energy etc,so it provides a greater space for the subsequent application of Pickering emulsion stabilized by inorganic nanoparticles.Based on the above considerations,two components of nano silica and nano titania were used as stabilizer.Firstly,SiO₂ nanoparticles were obtained by hydrolysis of TEOS which was catalyzed by L-lysine.TEM and Malvern laser particle size analyzer showed that the nano silica synthesized by a method which is different from the traditional Stober method was highly monodisperse and the particle size was less than 50 nm.Because the surface of nano silica be abundant in hydroxyl group,so it shows strong hydrophilicity.However,SiO₂ nanoparticles which are too hydrophilic can not form stable Pickering emulsions.Based on this consideration,it is necessary to conduct hydrophobic modification on the surface of the particles.Lastly,by means of TG,FT-IR,Contact angle,Lipophilicity and Activation index,we can prove that the organic components was successfully grafted to the surface of SiO₂ nanoparticles,achieved the target of hydrophobic modification.With nitric acid as inhibitor,nano titania sol was synthesized by sol-gel method.And TiO₂ nanoparticles with different crystal structure,which can be analyzed by XRD,were obtained by calcination at high temperature.Next,for hydrophobic modification of nano titania,the effect of 3-mercaptopropyltriethoxysilane content,modification time and temperature on hydrophobicity were investigated by using single factor experiment.Using SiO₂/TiO₂ nanoparticles as stabilizer and glyceryl triacetate as a new oil phase,the prepared Pickering emulsion has more potential applications,Such as cosmetics,plastics,food and other fields.The microscopic morphology of emulsion was observed by optical microscope and emulsion type was judged by drop test.The results show that with the increase of concentration of SiO₂/TiO₂ nanoparticles,the average diameter of droplet decreases from 40?m to about 10?m.When the two-component particles were dispersed in water firstly,the type of Pickering emulsion formed was O/W type,while firstly dispersed in glyceryl triacetate was W/O.The smaller the particles size of nano silica,the smaller the average diameter of the Pickering emulsion droplets.With the degree of hydrophobic modification of SiO₂nanoparticle in the two components increased,the emulsion type changed from O/W to W/O.When concentration of KCl was 0.1 mol/L,the stability of Pickering emulsion was the strongest,and the average diameter of droplet was the smallest.The concentration of SDS can cause the phase transition of emulsion.When pH reaches in3.02,the stability Pickering emulsion was the strongest,while it is greater than 6.62,emulsion breaks.