Study On High Strength Hydrogels Cross-linked By Zr?OH?₄ Nanoparticles

Hydrogels is a kind of soft materials that consist of cross-linked polymer networks and large amounts of water.In this thesis,in order to solve the problem that conventional hydrogels always display weak mechanical properties,we used the method of zirconium hydroxide nanoparticles as multifunctional crosslinking agents to improve the performance of the hydrogel.In order to overcome the problems that nanoparticles were difficult to be dispersed in water,with high solid content zirconium hydroxide nanoparticle sol were prepared by the sol-gel method,in which the zirconium acetate was used as a precursor and the ammonium hydroxide as a hydrolysis promoter.The nucleation mechanism,microstructure,particle morphology and other characteristics were investigated.In this thesis,zirconium hydroxide nanoparticles were successfully utilized as inorganic cross-linking agents to prepare novel high strength and stimulus responsive nanocomosite hydrogels using acrylic acid?AA?,N,N-dimethyl acrylamide?DMAA?,acrylamide?AM?and N-isopropylacrylamide?NIPAM?as monomers via in situ free-radical polymerization.The cross-linking mechanisms,microstructures,mechanical properties,swelling properties and other specific characteristics were systematically investigated.The main contents and conclusions are as follows:1.Zirconium hydroxide nanoparticles sol was prepared by the sol-gel method,in which the zirconium acetate was used as a precursor and the ammonium hydroxide as a hydrolysis promoter.The structure,size and the morphology of the zirconium hydroxide nanoparticles were studied by using transmission electron microscopy?TEM?,X-ray diffraction?XRD?,Fourier transform infrared spectroscopy?FTIR?,Raman spectroscopy,and Dynamic light scattering?DLS?.The results showed that the structure of the sol core was consist of the zirconium multimer,zirconium tetramers constantly lose protons to be condensation under the action of alkaline electrolyte;Structure of double electrode layer was consist of acetic acid ions,the colloidal particles were not easy to gather;The size of the nanoparticles is about 20nm;Crystal structure of nanoparticles is a standard zirconium hydroxide crystal particles.2.A series of P?AA-co-DMAA?/Zr?OH?₄ nanocompoite hydrogels?ZAD gels?with different monomer contents were synthesized by in situ free-radical polymerization of AA and DMAA using Zirconium hydroxide nanoparticles(Zr?OH?₄ NPs)as cross-linking agents.The cross-linking mechanism of ZAD gels was contribute to the hydrogen bond and coordination interactions between carboxylic groups on polymer chains and hydroxy groups on the surface of Zr?OH?₄ NPs.When the nanoparticles content was 20%,as the increasing of AA content in the initial solution,the cross-linking densities of ZAD gels increased,leading to the increasing of elastic moduli and decrease in toughness.When the AA ratio was higher than 15%,the obtained ZAD gels were brittle and stiff,lack of toughness.ZAD gels were able to process higher mechanical strengths after the swelling equilibrium.The size of 0.5 mm film was prepared by ZAD gels with good transmittance and continuous anti-fog performance.3.A series of P?AA-co-AM?/Zr?OH?₄ and P?AA-co-AM-co-NIPAM?/Zr?OH?₄nanocompoite hydrogels?ZAM gels and ZAMN gels?with different monomer contents were synthesized by in situ free-radical polymerization of AA,AM and NIPAM using zirconium hydroxide nanoparticles(Zr?OH?₄ NPs)as cross-linking agents.The cross-linking mechanism of ZAM and ZAMN gels was contribute to the hydrogen bond interactions between carboxylic groups,amino groups on polymer chains and hydroxyl groups on the surface of Zr?OH?₄ NPs.Because the hydrogen bond interactions and coordination between carboxylic groups and hydroxyl groups was stronger,when the nanoparticles content was 20%,as the increasing of AA content in the initial solution,the cross-linking densities of ZAM gels increased,leading to the increasing of elastic moduli and decrease in toughness.ZAM gels were able to process higher mechanical strengths after the swelling equilibrium.Because of the introduction of NIPAM,the ZAMN gels exhibited temperature-sensitivity.Taking the advantage of the different shrinking behaviors of ZAM gels and ZAMN gels in 20%NaCl solution,hydrogel biayer with bidirectional bending and reversible shape changing behaviors was prepared.