The Preparation And Research Of Janus Particles Via Pickering Emulsion Method

Janus particles refers to a class of particles having opposite chemical properties or chemical composition in different surface region.Such particles has demonstrated attractive prospect in molecular recognition and self-assembly,optical biosensors,interface modification,electronic paper,probe anisotropy imagination,solar energy conversion,and surface active agent.At present,there are many methods to prepare Janus particles including microfluidic synthesis,electric-fluid jetting,topological surface modification,self-assembled template,pickering emulsion method and controlled phase separation.In the previous study,submicron or micrometer-sized Janus particles were prepared by using nano-SiO₂ precursor particles which diameter is above 150 nm.In this study,the ARGET-ATRP polymerization method was applied to successfully synthesize the Janus nanoparticles below 100 nm under the condition of forming pickering emulsion.The size of monodispersed spherical Nano-SiO₂ particles below 100 nm were prepared by Stober method in this paper.And the controlled variable method was used to study the influence of the amount of ammonia as catalyst on the formation of SiO₂ microspheres.The result shows that The size of monodispersed spherical Nano-SiO₂ particles below 100 nm are obtained with 3.00 mL TEOS and 3.00 mL ammonia,and then surface-modified by using 4-（Chloromethyl）-phenyltrimethoxysilane to get nano-silica spheres initiator SiO₂-Cl.After that the nano-SiO₂ microspheres were dispersed in different polar solvent to characterize surface polarity of the nano-SiO₂ microspheres before and after modification with different amount of modifying agent.The excellent SiO₂-Cl microspheres can be prepared with 0.8g nano-SiO₂ and 1.00 mL modifying agent.Janus nanoparticles were prepared by the ARGET-ATRP polymerization under the condition that a stable Pickering emulsion was formed in two-phase system with SiO₂-Cl as the initiator.The effects of various factors on the preparation of Janus nanoparticles were studied as follows: The stability of Pickering emulsion before and after the polymerization was found to be more stable after the reaction.With the increase of the chain length in the polymerization process,the viscosity of the emulsion will raise.Either W / O type or O / W type of the Pickering emulsion will successfully get Janus nanoparticles by ARGET-ATRP polymerization.However,the morphology and dispersion of the nano-sphere particles under the transmitssion electron microscope（TEM）show that the Janus nanoparticles prepared under the W / O emulsion condition are better.DMAEMA and tBMA were chosen as the hydrophilic and hydrophobic monomers respectively.Because the monomer with higher reactivity for the polymerization reaction can play an important role in preparing excellent morphology and chemical properties of Janus nanoparticles,given that hydrophilic and hydrophobic monomers have different reactivites and chemical properties in a certain reactive condition.The modifying agent and monomer determine the stability and distribution of nano-sphere particles at the interface of the two phase system respectively.The best dispersed Janus Nano-SiO₂ particles whose surface activity is excellent when the concentration is 0.1g / L can be achieved with 1.00 mL modifying agent,2.00 mL hydrophilic monomer and 3.00 mL hydrophobic monomer.