Morphology Control Of Polymeric Nanoparticles Based On Poly(N-isopropylacrylamide) Ionic Microgels

Polymer nanoparticles are widely used in the fields of chromatographic analysis,coating,emulsion polymerization,drug carriers and model studies,and their morphology has an important impact on their performance.In this dissertation,poly(N-isopropylacrylamide)(PNIPAM) ionic microgels were used as the research platform.By using their properties of hardness,thermosensitivity and weak ionic bond,the morphology of the nanoparticles was regulated in emulsion/dispersion polymerization.Spherical,octopus-like,core-shell structure and raspberry-like nanoparticles were obtained.The specific contents of each chapter are as follows: 1.Study on Formation Kinetics of PNIPAM Ionic MicrogelsIn this chapter,the formation process of poly(N-isopropylacrylamide)(PNIPAM) ionic microgels was investigated by transmission electron microscopy and dynamic light scattering.In the first hour,the PNIPAM ionic microgels with loose structures were first formed.Then the loosely structured microgels gradually disintegrated in a short period of time.During the disassembly process,the dissociated nano-fragments reassembled into microgels with a more compact structure.Finally,the thermal sensitivity of the obtained PNIPAM ionic microgels was characterized.It was found that PNIPAM ionic microgels had a wide temperature transition range.As the temperature increased,the particle size decreased.2.PNIPAM Ionic Microgels as Particulate Stabilizer For Morphology Control of Spherical NanoparticlesIn this chapter,PNIPAM ionic microgels with different softness and particle size were first prepared and then used as particulate stabilizer for the dispersion polymerization of styrene.The experimental results showed that the stabilizing effect of the particulate stabilizer was related to the softness and particle size of the particles.Increasing the flexibility of the particulate stabilizer and decreasing the particle size of the particulate stabilizer could both enhance the stabilizing capacity.However,increasing the flexibility of the particulate stabilizer had better effect than decreasing the particle size of the particulate stabilizer in enhancing the stabilizing capacity.Considering the physical barrier function of dispersing agents,a possible mechanism was put forward.3.PNIPAM Ionic Microgels as Seeds For Morphology Control of Octopus-like NanoparticlesIn this chapter,the thermo-sensitivity of PNIPAM ionic microgels in a methanol-water system was investigated.The results showed that the PNIPAM ionic microgels lost their thermo-sensitivity in pure methanol solution,while they gradually restored their thermo-sensitivity with the increase of water content in methanol-water system.By using their thermo-sensitivity in methanol-water system,octopus-like nanoparticles were prepared by dispersion polymerization of styrene.It was found that in methanol-water system,PNIPAM ionic microgels became hydrophobic due to their thermo-sensitivity at the polymerization temperature,so that the polymerization of styrene occurred within the PNIPAM ionic microgels.However,styrene also had good solubility in the methanol-water system,so that the polymerization of styrene could occur outside the PNIPAM ionic microgel.Due to the hydrophobic interaction,the polystyrene formed outside the PNIPAM ionic microgels adsorbed onto the surface of the PNIPAM ionic microgels,and further developed into a smoother spherical polystyrene nanoparticle to form the “head” portions of octopus-like nanoparticles.The polystyrene generated within the PNIPAM ionic microgels was phase separated from the PNIPAM ionic microgels,forming protrusions on the surface of the microgel to form "claw" portions of the octopus-like nanoparticles.In this way,the octopus-like nanoparticles were obtained.4.PNIPAM Ionic Microgels as Seeds for Morphology Control of Core-Shell NanoparticlesIn this chapter,PNIPAM ionic microgels were used as seeds for emulsion polymerization of styrene and core-shell nanoparticles were obtained.The particle size and composition analysis of the core-shell nanoparticles showed that the particle size of the core-shell nanoparticles was smaller than that of the PNIPAM ionic microgels.And the polystyrene constituted the core of the core-shell nanoparticles,while the PNIPAM ionic microgels constituted the shell of the core-shell nanoparticles.The kinetics of the formation process of the core-shell nanoparticles showed that the styrene polymerized inside the PNIPAM ionic microgels and the resulting polystyrene bulged on the surface due to the phase separation with the PNIPAM ionic microgels.With the progress of polymerization,the polystyrene nanoparticles gradually became larger and the protrusions also became larger.Eventually,the protrusions dissociated from the surface of the PNIPAM ionic microgel to form spherical nanoparticles with core-shell structure.Studies on its dissociation behavior showed that the electrostatic repulsive force between polystyrene nanoparticles inside PNIPAM ionic microgels and the weak ionic interactions of PNIPAM ionic microgels played important roles in this dissociation.As an application,a photonic crystal array film was prepared by using the core-shell nanoparticles,which exhibited excellent optical property: the color of the film changed from red to green as the viewing angle changed.