Preparation And Characterization Of Smart Polyelectrolyte Brushes Composite Nano-particles

Smart materials have increasingly attracted the attention of researchers, and became the hotspot of materials science research. Smart nanoparticles is an important branch of smart materials has been broad applied in controlled catalysis, controlled drug delivery, sensors, micro-drivers, etc. In addition, there are a class of nanoparticles are anisotropic in shape or surface functionality with special self-assembly and stimulus-response capability, known as the Janus nanoparticles, which are also smart nano-materials showing a great potential applications.A series type of smart nanoparticles has been synthesized based on spherical polyelectrolyte brushes (SPB) in this article, including temperature/pH double-responsive nano spherical polyelectrolyte brushes, SPB/silica composite microspheres; With an assistant of Pickering emulsion method, pH-responsive anisotropy polyelectrolyte brushes were prepared through grafting nonsperical poly (acrylic acid)(PAA) brushes onto nano-sized core surfaces by photo-emulsion polymerization, and the morphology, stimulate-response and self-assembly of the microspheres were characterized by atomic force microscopy (AFM); more over, polyer/silica and magnetic-responsive Janus composite microspheres were also synthesized. Details are listed as follows:1. Isopropylacrylamide (NIPA) and acrylic acid (AA) copolymer were grafted onto the PS core surface by the light emulsion polymerization to obtain a pH and temperature bifunctional spherical polymer brush (BSPB). The dynamic light scattering (DLS) studies showed that the pH-responsive behavior of BSPB occurs lag compared to the homopolymer poly (acrylic acid)(PAA) brush. In addition, we used AFM to observe the morphology of BSPB in the gas and liquid, and to qualitatively analyze its surface adhesion by force curves. It was found that the surface adhesion responses to the pH value that increasing with increases of pH, and show low-sticky in pH value=3.2. Using PAA SPB as a template, SPB/silica core-shell and hollow microspheres was synthesized with a diameter ca.100nm. Compared to neutral brush polyvinylpyrrolidone (PVP), PAA anionic spherical polyelectrolyte brush is a more ideal template for in situ deposition of silica. The effect of the PAA brushes thickness, the salt concentration and temperature on silica deposition were discussed in the thesis. The DLS data proved that the hollow microspheres still have pH-response, and core-shell and hollow structure microspheres with good dispersion properties in water.3. PAA Janus polyelectrolyte and PS/SiO2Janus microspheres were prepared by Pickering emulsion method. Specific synthesis strategies include:1) After formation of Pickering emulsions, PS core embedded into paraffin wax surface, and the exposed part of the surface grafted PAA brush under UV irradiation to obtain non-spherical PAA brushes;2) PS/SiO2microspheres Janus nanoparticles were fabricated by asymmetric wet-etching based on Pickering emulsion;3) in the Pickering emulsion, styrene monomer asymmetrical swelled the PS/SiO2microspheres and then polymerized to obtain asymmetric SiO2shell structure. The effects of concentration and system stirring speed on Pickering emulsions were investigated. AFM probe modification and PAA brush incomplete drying was used to make a sharp contrast with the PS core in AFM images.4. Iron oxide nanoparticles of10nm were made by coprecipitation method. Magnetic Janus microspheres of100nm with a half of Fe3O4and a half of polystyrene were synthesized through phase separation by miniemulsion. Furtherly,200nm and450nm PS/Fe3O4magnetic Janus microspheres were prepared by seed emulsion polymerization. Using200nm PS/Fe3O4magnetic Janus microspheres as a template, respectively, PAA@PS/Fe3O4magnetic Janus brush and Pd@PS/Fe3O4magnetic Janus microspheres were prepared by photo-emulsion polymerization and the shadow vapor deposition. The thicknesses of Magnetic Janus brushes changed with pH as observed by DLS; The saturation magnetization and morphology of the magnetic Janus microspheres and brushes were investigated. The self-assembly of Janus microspheres controlled by an external magnetic field was observed.5. The polarity and surface charge of the substrate surface, the deposition temperature and the concentration of spherical brushes which influenced the self-assembly of spherical brush were discussed in this thesis; AFM was used to observe the orientation of Janus brush upon different surface.