| Summary: | 博士 === 國防大學理工學院 === 國防科學研究所 === 98 === Two different strategies were adopted in this study to prepare functionalized polystyrene (PS) microspheres. On the one hand, a synthetic method developed for preparation of sulfate- and carboxyl-functionalized polystyrene spheres that can be further decorated with gold (Au) nanoparticles is reported. On the other hand, the synthesis of amphoteric polystyrene latex particles, using a mixture of cationic ((V50, 2-Amino-Propane) Dihydrochloride) and anionic (KPS, Potassium Persulfate) initiators in a surfactant-free emulsion polymerization reaction is investigated. Based on this method, monodisperse PS microspheres with surface carrying two functional groups (-SO4- & -NH2) can be synthesized. The size of the microsphere and the density of surface functional groups can be easily tuned simply by controlling the concentrations of monomer and initiators in the reaction mixture.
The sulfate group is inherent in KPS for initiating the polymerization of PS, and eventually it acts as the reducing agent for the reduction of noble metal nanoparticles, such as Au and Pd, without external reducing agent after the solution is heated to 80℃. The inorganic-organic hybrid microspheres are, thus, formed. This technique can be further utilized to prepare magnetic microspheres. Firstly, the hybrid magenetic particles were formed in situ by encapsulation of pre-formed iron oxide nanoparticles during suspension polymerization of styrene with sodium dodecyl sulfate (SDS) used as the stabilizer. These hybrid magenetic particles with a saturated magnetization of 35 ~ 45 emu/g were used as the seed in the subsequent surfactant-free emulsion polymerization reaction. Depending on the initiator used (KPS and/or V50) in the surfactant-free emulsion polymerization process, the resulting functional magnetic microspheres with single functional group (SO4-) or bi-functional groups (-SO4- & -NH2) residing on their surfaces were obtained. Similar to the functionalized PS microspheres, noble metal ions can be reduced and deposited on the surface of microspheres to form polymer metal composite microspheres which showed magnetic properties. It is expected that magnetic microspheres will have more and more potential to apply in biomedicine and other fields.
One the one hand, the dispersion of functional polystyrene microspheres was stable and free of coagulation owing to the presence of sulfate groups on their surfaces. On the other hand, the functional sulfate groups are able to react with noble metal ions further and nano-sized metal nanoparticles were substantially depositing onto the surfaces of PS spheres in dot-arrayed pattern without adding any extra reducing agent. In addition, it was found that the amine group coming from the initiator, V50, effectively anchored and stabilized metal nanoparticles for a long period of time.
The particle size and Zeta potential of the microspheres were determined by dynamic light scattering (DLS). It was shown from the DLS results that the concentrations of initiator and monomer are the most significant parameters to control the size and surface charge of the microspheres. Fourier Transform Infrared Spectrometer (FTIR) spectroscopy was employed to study the composition and surface functionality of PS microspheres. The data confirmed that the polymer microspheres consisted of Sulfate Group (-SO4-) and Amidinium based group (HN=CH-NH2). Transmission Electron Microscope (TEM) results showed that the metal nanoparticles anchored were distributed uniformly on the surfaces of microspheres and the average sizes were less than 5 nm for all samples. The presence of metal particles on the surface of microspheres was confirmed by Energy Dispersive X-Ray (EDX). From the ESCA analysis, it can be concluded that the polymer microsphere can stabilize Au colloids mainly due to the formation of complexes of gold ions (Au3+) with amine functional groups on the surface of the microspheres and the Au3+ complexes were, then, converted to Au-NPs by reduction via the sulfate groups. To study the catalytic properties of functional microsphere-stabilized noble metal nanoparicles, the reduction of 4-nitroanilline to 4-phenyleneamine was used as a model reaction. Our results showed that both of the microsphere supported Pd and Au had higher catalytic activity than that of commercial Pd/C catalyst. Moreover, when the Pd-PS was used as catalyst, the reduction reaction of 4-nitroanilline was completed within 35S with a Pd content of 1.09 wt.%. The magnetic microspheres with the ability to respond to an external magnetic field can be fabricated based on this study simply by encapsulation of magnetic nanoparticles introducing magnetic particles. It will raise their value in applications.
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