Study Of Silver Nanoparticles Loaded Temperature Stimulus Responsive Hybrid Nanogels

Silver (Ag) nanoparticles have many unique properties, such as surface plasmon resonance, bactericidal and catalytic activity for some reactions, if Ag nanoparitcles and stimulus responsive polymer are combined, the properties of the Ag nanoparticles within the formed hybrid polymer materials can be changed can be changed in response to external stimuli, so they have an attractive application prospect in sensor, surface-enhanced Raman spectroscopy, microreactor and medical diagnosis, etc. Stimulus responsive nanogel, also referred to as intelligent nanogel, is a kind of stimulus responsive polymer nanomaterial with of the particle sizes ranging from 1 to 1000 nm, which is able to respond to external stimuli and undergo volume phase transition. It has some characteristics, such as fast response rate, dispersion stability in aqueous medium, good biocompatibility, the ability to cross many biological barriers, and so on. In this thesis, Ag nanoparticles were directly loaded into temperature stimulus responsive poly(N-isopropylacrylamide) (PNIPAM) nanogels by in-situ reduction reaction It was found that the surface plasmon resonance property and the catalytic activity of the Ag nanoparticles inside the formed hybrid nanogels are pronouncedly dependent on the environmental temperature. The majorresearch work and obtained results include the following three parts.(1) The Ag nanoparticles loading hybrid nanogels were prepared by in-situ reduction of Ag+ ions coordinated into PNIPAM nanogels by NaBH4. The weight content of the loaded Ag nanoparticles within the hybrid nanogels is raised with increase of the crosslinking density of the PNIPAM nanogels or the used amount of AgNO3 and NaBH4, and their maximum value reachs 25.5%. The Ag nanoparticles are homogeneously distributed within the hybrid nanogels. Their average particle sizes are within the range from 8 to 12 nm, and they are increased with the increase of the amount of AgNO3 and NaBH4 used. The hybrid nanogels exhibit spherical shape and have good monodispersity. Their particle sizes and swelling ratios decrease with increasing the content of the loaded Ag nanoparticles. The interaction between Ag nanoparticles and PNIPAM polymer chains inside the hybrid nanogels has been confirmed by Fourier transformation infrared spectroscopy results.(2) The Ag nanoparticles loaded hybrid nanogels have temperature stimulus responsiveness like pure PNIPAM nanogels. Their temperature stimulus responsiveness is weakened with increase of the content of the loaded Ag nanoparticles. The Ag nanoparticles inside the hybrid microgels have the optical property of surface plasmon resonance like colloidal Ag nanoparticles. The position, strength and half-height width of the maximum peak of their ultraviolet and visible absorption spectra can be changed as the temperature of their aqueous medium varies, and the most striking variation occurs during their volume phase transition.(3) The Ag nanoparticles loaded hybrid nanogels have catalytic activity for the reduction reaction of 4-nitrophenol by NaBH4. The variation process of the apparent reaction rate constants with the reaction temperature change can be divided into four stages, which is related to their volume phase transition,so the rate of the reduction raction can be adjusted by reaction temperature. In addition, the apparent reaction rate constants are linearly raised with increasing the hybrid nanogels concentration.