Preparation Of Janus Nanocomposites By Pickering Emulsion And Application In Self-healing Hydrogels

Due to the excellent mechanical strength and large specific surface area of the nanomaterials,the self-healing nanocomposite hydrogels have outstanding self-healing properties,mechanical strength and biocompatibility.As anisotropic functional materials with unique morphology or physical and chemical properties,Janus nanomaterials have become the focus in the application of self-healing nanocomposite hydrogels.In this graduation thesis,based on the development of Pickering emulsion method for designing Janus nanocomposites,a variety of silica（SiO₂）-based Janus composite nanosheets were successfully prepared using the oil-in-water Pickering emulsion system.After implanted into polymer networks,Janus nanocomposite self-healing hydrogels were successfully prepared.The unique structure of Janus nanomaterials enables the designed nanocomposite hydrogels to realize the synergy of a variety of reversible non-covalent bonds,and thus have outstanding self-healing properties.The content is mainly composed of three parts:1.A new methodology research of atom transfer radical polymerization（ATRP）under oil-in-water Pickering emulsion conditions.The development of Pickering emulsion systems with better stability and"active"/controllable properties which using the nanomaterials as emulsifiers is one of the hotspots of current research.Triethylamine（TEA）and deionized water as the water phase.The mixture of Eosin Y,ethyl 2-bromoisobutyrate（EBiB）and methyl methacrylate（MMA）as the oil phase.Using the cellulose nanocrystals（CNCs）as emulsified particle,the controlled polymerization of MMA in the Pickering emulsion environment was successfully achieved.The polymerization of MMA shows the typical“living”/controlled characteristics with controllable molecular weight（150,100 g/mol～219,100 g/mol）and low M_w/M_n（1.10～1.25）.Therefore,an ATRP methodology under Pickering emulsion based on nanoparticles as a solid surfactant was successfully developed.2.The design of Janus nanocomposite self-healing hydrogels with excellent mechanical strength and self-healing properties by Pickering emulsion.Specifically,the pH value of the mixed solution was adjusted to about 2.5 by using hydrolyzed styrene-maleic anhydride copolymer（HSMA）.And this mixture was as the aqueous phase.Tetraethyl orthosilicate（TEOS）,3-（trimethoxysilyl）propyl methacrylate（MPS）and 3-aminopropyltrimethoxysilane（APTMS）was dispersed in n-dodecane as oil phase.The aqueous phase was mixed with the oil phase,and a stable Pickering emulsion is obtained by high speed homogenization.Under acidic conditions,silica Janus hollow spheres（SiO₂ Janus Hollow Spheres,SiO₂ JHSs）with double bond termination on the inside and amino group termination on the outside were prepared by the sol-gel self-assembly method at the emulsion interface.Based on mussel-inspired chemistry,dopamine（DA）was self-polymerized and coated on the surface of SiO₂JHSs in the Tris-HCl buffer.The silica@polydopamine Janus hollow spheres（SiO₂@PDA Janus Hollow Spheres,SiO₂@PDA JHSs）were further obtained.SiO₂@PDA Janus composite nanosheets（SiO₂@PDA Janus Nanosheets,SiO₂@PDA JNs）were successfully prepared by ultrasonic crushing the SiO₂@PDA JHSs.SiO₂@PDA JNs were further implanted into polyacrylic acid（PAA）network by free radical polymerization with potassium persulfate（KPS）as initiator.After 4 hours of healing,the healing-efficiency of SiO₂@PDA nanocomposite self-healing hydrogels can reach up to 90.4%.The mechanical strength have significantly improved and are about three times than PAA hydrogels.3.Janus nanosheets constructed dual self-healing nanocomposite hydrogels with high mechanical strength and rapidly self-healing properties.Specifically,SiO₂ JHSs were obtained by the emulsion interface sol-gel self-assembly method.2-（Acryloyloxy）ethyl ferrocene carboxylate（MAEFc）dispersed in oil phase can polymerize by free radical polymerization,and graft on the SiO₂ JHSs inner surface by using sol-gel self-assembly method under emulsion interface with KPS as initiator.The SiO₂@PMAEFc/PDA JHSs were further prepareed by coating the PDA onto the surface of SiO₂@PMAEFc JHSs,and then crushed the SiO₂@PMAEFc/PDA JHSs to obtain the SiO₂@PMAEFc/PDA Janus nanosheets（SiO₂@PMAEFc/PDA JNs）.As reinforcing materials,SiO₂@PMAEFc/PDA JNs were composited into the poly（acrylic acid/acryloyl-β-cyclodextrin）(P（AA-co-ACD）network to prepare nanocomposite self-healing hydrogels.The obtained SiO₂@PMAEFc/PDA hydrogels have excellent self-healing properties（self-healing efficiency:92.4%）and high mechanical strength（stress:2.23 MPa）.