Preparation And Morphology Control Of Anisotropic (Janus) And Multihollow Polymer Particles

The development of polymer particles has great influence on our economy and life. For example, polymer particles have increasingly become an important subject with desirable physical properties applied as coatings, light-sensing materials, bio-medicine, and so on. Since the morphology and size of particles is the key factors to determine potential applications of polymer particles, great interest has been focused on the morphology control of polymer particles. Various of morphological particles have been prepared. Amongst, Janus particles and multihollow polymer particles have received considerable attention over the last decade. Because of its anisotropic surface chemical composition compared with a homogeneous shape, Janus particles have some unique properties. However, due to the asymmetric feature in the particles, the preparation of Janus particles remains challenging for a long time. The final morphology is determined by the competition between thermodynamic and kinetic factors. Multihollow polymer particles have a unique advantage in a low density and high specific surface area. Because the formation mechanism of Janus and multihollow particles involves the interactions between thermodynamic and kinetic factors, the preparation and morphology control of Janus and multihollow polymer particles have great significance not only in enriching the theory in interface and colloid surface science, but also in expanding their practice application fields. This paper aims at the preparation of Janus and multihollow polymer particles with controllable morphologies from different emulsion system (seed emulsion, miniemulsion, Pickering emulsion) based on the interface physical chemistry theory. The main content is as following:1. The effects of the concentration of polyoxyethylene octylphenyl ether (OP-10) as a nonionic surfactant and the molecular weight of polymers (polystyrene (PS) and poly (methyl methacrylate) (PMMA)) on the morphology of anisotropic PS/PMMA composite particles were investigated. In the case of polymers with lower molecular weight (Mws≈6.0×104 g/mol), the PS/PMMA composite particles have dimple, via acorn, to hemispherical shapes along with the increase of the OP-10 concentration. On the other hand, when the polymers have higher molecular weight (Mw≈3.3×105 g/mol), the morphology of PS/PMMA composite particles changed from dimple, via hemispherical, to snowman-like structure while the concentration of OP-10 was increased. This work first studied on the influence of molecular weight of PS and PMMA on the final morphology of anisotropic PS/PMMA composite particles. Furthermore, thermodynamic analysis was first discussed from the viewpoint of spreading coefficients:The results indicated that both the concentration of OP-10 in aqueous solution and the molecular weight of polymers were very important to the final morphology of anisotropic composite particles.2. Snowman-like polymer particles were prepared by radiation seed emulsion polymerization. The monodisperse crosslinked PS seed particles with surface modified by carboxyl groups were first prepared by emulsifier free emulsion polymerization. These seed particles were first swollen by monomer, and then the polymerization was induced by 60Co y-ray. During the polymerization, a new phase was pushed out by elastic stress, and the snownman-like polymer particles were formed. The effects of the weight ratio of seed/monomer, pH, and the dose rate were examined in detail. Finally, we found radiation seed emulsion polymerization was an efficient way to produce snownman-like polymer particles at room temperature.3. Hybrid Janus particles were prepared by radiation miniemulsion polymerization. (1) Novel PS/silica hybrid particles with various morphologies were first prepared byγ-radiation miniemulsion polymerization in the presence of partially modified silica particles. The final morphology depends on the weight ratio of monomer/silica. The PS/silica hybrid Janus particles present mushroom-like, hollow-egg-like and bowl-like structures respectively, with the increase of the weight ratio of monomer/silica. The formation mechanism of the anisotropic PS/silica hybrid particles related with the droplet nucleation of miniemulsion polymerization; (2) In addition, we presented a facile route to prepare a new type of polystyrene nanobowls (there was a small hole at the bottom of each nanobowl) by phase separation during radiation miniemulsion polymerization. The nanostructures could be easily controlled by the weight ratio of monomer/silica. Furthermore, this nanostructure was first discovered, which could have wide potential applications, such as, controlled drug release system and catalytic applications; (3) Furthermore, the hybrid materials were prepared by simultaneous polymerization of silane coupling agent and organic monomers. During the polymerization, phase separation happened and novel morphologies were obtained.4. Novel walnut-like multihollow polymer particles were first prepared byγ-ray radiation emulsion polymerization using the crosslinked and sulfonated polystyrene spheres (CSP) as the template. The formation process was studied in detail and the morphology of walnut-like multihollow polystyrene particles could be controlled by the content of crosslinking agent, sulfonation time of CSP particles and the weight ratio of monomer/CSP. In addition, bonding Ag nanoparticles onto the surface of walnut multihollow polymer particles was achieved, which could be extended to other noble metal nanoparticles and have wide range of potential applications, such as catalysts, sensors, solar cells and photonic crystals.5. Cage-like multihollow polymer particles were prepared by non-polymerization method. Sulfonated PS particles were first dispersed into the mixture of water and ethanol, and then a certain amount of heptane was added. The sulfonated PS particles were swollen by the mixture solvent and heptane. Cage-like polymer particles were obtained after cooling down to room temperature. Both the heating temperature and the ratio of water/ethanol were important to the final morphology of multihollow polymer particles.