Fabrication Of Janus Silica Nanomaterials And Their Application In Pickering Emulsions

Janus nanomaterials with asymmetric physical and various chemical properties have broad application prospects in the fields of catalysis,drug delivery,emulsification,and sensing.Various strategies have been developed by scientists to fabricate such type of nanomaterials,including phase separation method,immobilization method,self-assembly method.Structure and size of Janus nanomaterials can be adjusted flexibly by phase separation method,and above method is mostly applied in fabrication of organics and composites.Shielding effect of the immobilization method can be achieved during the selectively chemical modification process of Janus nanomaterials.However,most immobilized templates cannot be removed completely.The yield of Janus nanomaterials prepared by self-assembly method is relatively low.Moreover,the morphologies and structure of Janus nanomaterials are not easy to control.Therefore,there are still major challenges for the preparation of Janus nanomaterials.Herein,layered double hydroxides are used as immobilization templates for fabrication of three types of different morphologies and structures of Janus silica nanomaterials.(1)Negatively charged silica nanospheres are absorbed on the surfaces of the positively charged Co Al-LDH by electrostatic force,and exposed surfaces of silica are hydrophobically modified selectively,then LDHs are removed to obtain amphiphilic Janus silica nanospheres.(2)Using the above Janus silica nanospheres as seeds,silica is deposited onto the hydrophilic surface part,and attempt to prepare snowman-like Janus silica nanoparticles.(3)Silica is deposited onto the surfaces of Mg Al-LDH nanoplates,where block copolymer F127 is adsorbed.Outer shell surface is hydrophobically modified,then Mg Al-LDH templates are removed by acid etching to form amphiphilic Janus silica nanosheets.Using SEM and FT-IR to characterize the mid-product of synthesis process of Janus nanoparticles.In addition,the application of Janus silica nanospheres and Janus silica nanosheets in Pickering emulsions was studied in this work.As emulsifiers of Pickering emulsion,the amphiphilicity of Janus silica nanomaterials can enhance the interaction at the interface between oil and water phases.Janus silica nanosheets can only rotate along the axial direction at the interface,suggesting good space-based stability.The thinnest average thickness of Janus silica nanosheets is about 1.5 nm,which is much smaller than the size of emulsion droplets.They have good adhesion and isolation effect at the phase interface,which have advantages of traditional surfactants and solid surfactants.Pickering emulsion emulsified by 0.04 wt% of ultrathin Janus silica nanosheets can maintain stable state for at least 3 months.The additive amount of the Janus nanosheets for stabilization of Pickering emulsion is less than most solid emulsifiers as reported in literature.