Preparation And Characterization Of Gold Nanoparticles Loading Temperature Sensitive Microgels

Both spherical gold nanospheres (AuNSs) and rodlike gold nanorods (AuNRs) have the surface effect and the quantum size effect of metallic nanoparticles, so they exhibit the optical, electrical and catalytic properties different from macroscopic bulk gold. It is due to the surface effect that AuNSs or AuNRs have very high surface energy and are easy to be aggregated by themself, thus they need to be surface modified or loaded into certain carrier. If AuNSs or AuNRs are loaded into the intelligent microgels of stimulus responsiveness, the formed intelligent composite microgels not only have the properties of both simultaneously, but also the properties of AuNSs or AuNRs can vary in response to external stimulus. Therefore, the composite microgels have a good application prospect in drug delivery and controlled release, sensor, medical diagnosis, environment detection, intelligent microreactor, etc. In this thesis, Au/Ag alloy nanospheres were first synthesized and their formation mechanism was studied. Then, AuNSs or AuNRs were loaded into temperature sensitive poly(N-isopropylacrylamide)(PNIPAM) microgels, respectively, and the relationship between the localized surface plasmon resonance (LSPR) optical properties of the produced composite microgels and environmental temperature was investigated. The detailed research work and the obtained results of the thesis are as follows.(1) The Au/Ag alloy nanospheres of the diameter of13-40nm were synthesized using sodium citrate as reducing agent and stablizing agent. High resolution transmission electron microscopy (HRTEM) and small angle X-ray scattering (SAXS) were used to measure the diameter of the alloy nanospheres, and energy dispersive X-ray spectroscopy (EDS) was utilized to confirm that they consist of Au and Ag elements. Their particle sizes are increased with decreasing the used amounts of sodium citrate and increasing the amount of chloroauric acid. Their particle sizes increase with the used amount of AgNO3, whereas their shape changes from sphericity to spheroidicity. Their LSPR wavelength increases linearly with their particle size.(2) AuNSs loading PNIPAM microgels were prepared by two-step in-situ reducing AuCl4ˉcordinated into their networks. HRTEM, field emission scanning electron microscopy (FESEM) and atomic force microscopy (AFM) were used to characterize the morphological structure and surface topography of the generated composite microgels. Ultraviolet-visible spectroscopy (UV-vis) method was utilized to probe the reaction process, and it was found that the particle size of the AuNSs embeded into the microgels nearly keep constant after reaction time of12min. The particle sizes of the AuNSs are gradually increased with decreasing the used amount of hydroxylamine hydrochloride, but their monodispersity become poor. With increasing the amounts of hydroxylamine hydrochloride and chloroauric acid simultaneously, the diameters of AuNSs are gradually raised, but their weight contents show the tendency of lowering. AuNSs loading PNIPAM composite microgels have temperature sensitivity, and their LSPR property can alter reversibly with temperature. This behavior may be due to the following two reasons. The refractive index of PNIPAM microgels is increased with decreasing their water content after temperature change triggered their volume phase transition. The electromagnetic coupling between the embeded AuNSs is produced by their approaching after temperature induced shrinkage of the composite microgels.(3) AuNRs filled temperature composite microgels were prepared by growth of Au seeds within PNIPAM microgels by reduction action using ascorbic acid as reducing agent and cetyl trimethyl ammonium bromide as template. Low crosslinking density of PNIPAM microgels facilitate formation of AuNRs. As the used amount of AgNO3is raised, the aspect raitos of AuNRs inside PNIPAM microgels are increased. AuNRs filled PNIPAM are temperature sensitive. The transverse LSPR wavelength of their embeded AuNRs is independent of temperature, whereas their longitudinal LSPR wavelength is obviously redshifted whit temperature raising. The greater the aspect ratios of the AuNRs, the more significant the change of their longitudinal LSPR wavelength with temperature. The volume phase transition of PNIPAM microgels is the main reason for the longitudinal LSPR wavelength redshift of their filled AuNRs.