Study Of Silver Nanoparticles Loading Smart Composite Microgels

The smart composite microgels produced by loading silver nanoparticles (AgNPs) into smart microgels have the unique properties of AgNPs and the smart microgels, and the properties of AgNPs can vary in response to external stimulus. Therefore, they have fascinating potential applications in sensor, cell imaging detection, drug delivery and smart microreactor, etc. In this thesis, AgNPs were loaded into the pH/temperatrue dual stimuli responsive microgels with interpenetrating polymer network (IPN) structure to fabricate the smart composite microgels with dual stimuli responsiveness. The advantage of the dual stimuli responsive microgels is little interference between two kinds of stimulus responsive polymer networks. The relationships between localized surface plasmon resonance (LSPR) optical property and fluorescence property of the composite microgels and environmental temperature or pH value were mainly investigated. In addition, if smart composite microgels dispersed in aqueous medium are assembled into macroscopic materials, their application scope would be widened. Hence, Ag NPs loading pH stimulus responsive composite microgels were assembled into slice materials with stable structure by ice crystal templating method followed by post-crosslinking in the thesis. The valuable results in the thesis are as follows:(1) Based on the previous research work in our group, AgNPs loading pH stimulus responsive composite microgels were prepared with high efficiency. The average diameter of the AgNPs embeded inside the microgels is3.4±1.0nm, and their weight content is43%. Their LSPR optical property can change responding to pH stimulus. Then, the composite microgels were assembled into slice materials by ice crystal templating method, followed by adding the crosslinking agent and the catalyst to covalently link the neighboring microgels to stabilize the slice materials in aqueous medium. The formed slice materials are pH stimulus responsive, shrinking under pH3.0and swelling under pH7.0.(2) AgNPs were loaded into pH/temperatrue dual stimuli responsive microgels with IPN structure consisting of poly(acrylic acid)(PAA) and poly(N-isopropylacrylamide)(PNIPAM) by in-situ reduction method. The AgNPs were found to be homogeneously distributed within the formed composite microgels through high resolution transmission electron microscopy and their average diameters and weight contents are increased with the used amounts of the reactants, i.e. AgNO3and NaBH4. The results obtained by dynamic laser light scattering show that the composite microgels have temperature stimulus responsiveness under pH3.0or7.0and they have pH stimulus responsiveness at20℃or40℃, indicating that there is little interference between two stimulus responsive polymer networks inside the composite microgels. Their LSPR optical property can alter reversibly in response to pH or temperatrue change. The higher the AgNPs contents inside the microgles, the more remarkably their LSPR wavelengths change within the same temperature and pH range. This reveals that the effect of volume phase transition induced by temperature or pH stimulus on their LSPR optical property is enhanced with their AgNPs content.(3) The results of fluorescence spectra measurements exhibit that Ag NPs loading pH/temperatrue double stimuli responsive composite microgels have fluorescence property. The higher the Ag NPs contents within the microgels, the stronger their fluorescence effect. After analyzing the particle size and fine structure of the Ag NPs inside the composite microgels by HRTEM, it is considered that their fluorescence effect is presumably caused by the Ag nanoclusters with diameters less than2nm attached on the surfaces of the embeded Ag NPs or exsisting alone. Upon excitation of284nm light, the intensity and wavelength of the maxium fluorescence emission peak of AgNPs loading pH/temperatrue double stimuli responsive composite microgels can change reversibly with temperature or pH value. What’s more, they change most significantly within the same temperture or pH range as the volume variation of the composite microgels. As the AgNPs content inside the composite microgels is raised, the intensity of their maximum fluorescence emission peak is enhanced.