Preparation And Design Of Nanocomposite Hydrogels Based On Organic Nanoparticles And Functional Fabrication

Due to the 3D network structure and unique properties, polymer hydrogel reveals high potential applications in flexible chemical mechanical devices, selective-separation materials, biomedical and tissue engineering. However, conventional polymer hydrogel (OR gel) cross-linked by the chemical cross-linker always shows serious disadvantages in the weak mechanical properties which limit the application to a large extent. Recently, many types of novel hydrogel with good mechanical properties have been developed to overcome the limitations of OR gel. Among them, nanocomposite hydrogels (NC gel) reveals outstanding advantages:extraordinary mechanical properties and simplicity of synthesis. Besides, due to the unique polymer/clay network structures, the swelling properties and optical properties are also improved in NC gel compared with OR gel, thus it is reported that NC gel solves almost all the disadvantages of OR gel simultaneously. NC gel has attached wide attention due to the unique network structure and crosslinking interactions in recent years, the properties and structure for NC gel are also investigated by different methods. However the binding mechanism of polymer and clay in NC gel prepared by free-radical polymerization has not been clarified yet which severely restrict the development of NC gel. Furthermore, NC gel always shows little potential in fabricating particular functionality due to the special cross-linking interactions.According to the issues to be solved for NC gel, the binding interactions between polymer and clay in polyacrylamide (PAAm) NC gel are investigated, a novel organic nanoparticle composite hydrogel with excellent mechanical properties are prepared and a general approach is proposed to fabricate functional hydrogel with excellent mechanical properties and permanent functions by incorporating inorganic particles into the gel matrix. The detail content and results in this dissertation are summarized as follows:Firstly, the interactions between organic/inorganic components in pregel solution and in NC gel are studied, the non-covalent interactions between polymer and clay in NC gels and the forming process for NC gel network during free-radical polymerization are proposed. It is found that there exists hydrogen bonding interaction between clay platelets (full of hydroxyl and carboxyl groups on the surface) and amide group as well as the possible complexation of the metal ions on the clay surface by nitrogen atoms of AAm. So the interactions between PAAm and clay in NC gel are owing to the hydrogen bonding interaction and the possible complexation amongst them.Secondly, modified ZnO and Ag nanoparticles are integrated into OR gel to prepare hybrid hydrogel (Hy gel). It is revealed that the modified ZnO and Ag nanoparticles can disperse uniformly in pregel solution, thus the inorganic nanoparticles are uniformly dispersed in Hy gel matrix. The incorporated ZnO and Ag nanoparticles can effectively improve the mechanical properties for the Hy gel and endows the gel controllable swelling properties.Furthermore, PS nanoparticles with cationic surface are prepared by emulsifier-free emulsion polymerization, sulfate radicals can be absorbed on PS nanoparticles for the electrostatic interaction. In-situ polymerization of monomer is carried out on the surface of particles, and the formed attached chains can crosslinked each other to form a novel organic nanoparticle composite hydrogel (OC gel), PS nanoparticles are used as the crosslinking agent in OC gel. The gel reveals excellent mechanical properties and elasticity due to the uniform dispersion of PS nanoparticles in gel matrix, and the content of PS nanoparticles in pregel solution shows significant influence to the network structure and properties of OC gel.To achieve the controllable and rapid preparation for OC gel, synthesized polymerable photoinitiator is grafted on PS nanoparticles to fabricate photoactive PS nanoparticles. In-situ polymerization of monomer is carried out on the surface of particles under UV irradiation to prepare hydrogel, photoactive PS nanoparticles are used as the crosslinking agent. Due to the covalent interactions between PS nanoparticles and polymer, the hydrogel is a kind of covalent crosslinked nanocomposite hydrogel (CNC gel). CNC gel shows a better cell compatibility than OR gel because longer polymer chains are existed in CNC gel network. Fe3O4 magnetic particles are further incorporated into the photoactive PS nanoparticles to fabricate magnetic CNC gel with excellent mechanical properties. It opens up opportunities to fabricate stabilized functional hydrogel (e.g., fluorescence, photochromic or electrical properties) by incorporating functional inorganic materials into PS nanoparticles.The mechanism of network formation and fabrication of functional hydrogel are two important issues to be solved for NC gel. In this dissertation, the non-covalent binding interactions between polymer and clay in PAAm NC gel are proposed. In addition, a new approach is used to prepare functional nanocomposite hydrogel with high mechanical properties. In the future work, different functional inorganic nanoparticles can be incorporated into organic particles to prepare functional organic nanoparticles with surface initiated activity, these nanoparticles are used as the cross-linking agent to fabricate functional OC/CNC gel. The biomedical organic nanoparticles with surface initiated activity can also be used as the cross-linking agent to prepare biomedical OC/CNC gel, which can achieve the applications in biomedical field. On this basis, it is possible to prepare OC/CNC gel with multiple functions, which can further expand the application fields of polymer hydrogel.