| Polyelectrolyte brushes not only have all the natures of general polymer brushes, but also contain more prominent properties such as pH-responsive, temperature-sensitive, anti-ion adsorption. The polyelectrolyte brushes have been widely used in the areas of controlled drug releasing, sewage treatment, preparation of metal nanoparticles, catalysis, molecular detection and protein adsorption due to the above properties. For spherical polyelectrolyte brushes, the polyelectrolyte is grafted onto the spherical template particles. The formed spherical polyelectrolyte brushes with clear core-shell interfaces are generally in the size of10nm to500nm and the size of the template particles is in monodisperse distribution. Grafting polyelectrolyte on the surfaces of the template particles is the main way to prepare spherical polyelectrolyte brushes by chemical grafting. The surface-initiated atom transfer radical polymerization (SI-ATRP) is widely used in spherical polyelectrolyte brushes synthesis since it is not only able to control the morphology and performance of the target product, but also has a strong versatility and stability. In this paper, spherical polyelectrolyte brushes were prepared by SI-ATRP in aqueous medium and the effect of grafting ways and amount of the coupling agent on the product were discussed. We also explored some applications of spherical polyelectrolyte brushes, such as enhanced Raman fields and superhydrophobic surface. The main contents of the research are as follows:1. Monodisperse silica spheres were prepared by Stober method with a diameter of about230nm. Then they were grafted by different amount of coupling agent and initiator in proper order after being activated in the Piranha solution. After that, spherical PMMA brushes were prepared in the aqueous media by ATRP. At last the spherical PMAA brushes were obtained after hydrolysis of PMMA. The products were characterized by transmission electron microscopy (TEM), thermogravimetry (TG), Zeta potential (4), energy dispersive spectrometer (EDS), fourier transform infrared spectroscopy (FT-1R) and gel permeation chromatography (GPC). Results showed that the standing reaction was the best way for grafting of coupling agent and the optimal formula was that the amount of microspheres and the coupling agent was1g and4mL respectively. Trifluoroacetic acid should be increased moderately in the hydrolysis process.2. We regulated the molecular weight of the polyelectrolyte brushes by controlling the reaction time of ATRP. Then raspberry-like particles with different morphologies were synthesized by series of molecular weight polyelectrolyte brushes. The tetraethoxysilane (TEOS) was hydrolyzed in situ by diethanolamine (DEA) as catalyst. During the hydrolysis process of TEOS, surface nucleation from the sites and core growth processes coexisted in the whole system and different molecular weight had different effects on the different morphologies. When the molecular weight of polyelectrolyte brushes was0, a smooth core-shell structure was obtained; with the increasing of molecular weight uniform raspberry-like particles were appeared; with the molecular weight of the PMAA brushes increasing continuously, complex morphologies could be found from the same seed particles. The uniform raspberry-like particles were dispersed in ethanol to test the contact angle. The result was157.2°which indicated that the superhydrophic surface was obtained.3. Ag nanoparticles were prepared by polyelectrolyte brushes with different molecular weight as nanoreactor. AgNO3was adsorbed on the reaction site as the origin of Ag and then was reduced in situ by DEA. The results showed that the Ag nanoparticles’ shape and size could be easily controlled by adjusting absorption time and reduction time. SERS enhancement could be observed for nearly all the Ag nanoparticles when the concentration of R6G was10-6mol/L. However, when concentration of R6G was10-8mol/L, SERS enhancement could be observed only when the Ag particles had the larger size (>20nm). |
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