Preparation Of Poly (N-Isopropylacrylamide) Microgels By Using A Coaxial Microfluidic Device And Application In The Microreactor

Polymer gels with phase transitions are of interest for researchers in wide areas of science and technology, due to their great potential in both fundamental (experimental and theory) and application aspects. Poly(N-isopropylacrylamide) (PNIPAm) and its derivatives are well-known thermoresponsive materials which show a phase transition when triggered by external stimuli such as the solvent composition, pH, ionic strength, electric field and light. In order to meet the requirement for certain applications, such as controlled release of macromolecules for which the loading levels and release kinetics are directly affected by the polydispersity of the particles, microgels with a narrow size distribution are greatly demanded. Common synthesis techniques like emulsion polymerization, and solvent-free emulsion polymerization can produce PNIPAM microgels with a narrow size distribution. However, these microgels are of submicron size. Synthesis of monodisperse PNIPAM microgels with dimensions in the order of several hundrends microns are still more challenging. Recently, the developing microfluidic technology has presented to be a novel and shining method to fabricate microgels with size ranging from tens to hundreds of microns.In this thesis, common synthesis techniques for preparation microgels had been summarized; the merits and fabrication methods of the microfluidic devices had been introduced and the current development of the preparation of microgels using microfluidic devices had been reviewed. In this thesis, we prepared Poly(N-isopropylamide) mirogels using the N',N'-methylene-bisacrylamide(BIS) and clay as the chemical cross-linkers and physical cross-linkers respectively through a coaxial capillary microfluidic devices with low cost, in which the polypropylene(PP) hollow fibers were used as the main components.The production of two kinds of monodisperse PNIPAM microgels was confirmed by analysis with Fourier transform infrared spectroscopy. The influence of experimental parameters and processing on the size of microgel had been studied. The results showed that the size of microgels could be controlled conveniently by changing the tips of middle tubes using different PP hollow fibers, and it also could be controlled by tuning the different flow rates of the continuous phase and the surfactant concentrations in the continuous phase. The modified MWCNTs were suspended in the dispersed phase and the light-sensitive PNIPAm/Clay/MWCNTs nanocomposite microgels was fabricated in situ by using the coaxial microfluidic devices. The acid-treated MWCNTs and Clay-modified MWCNTs can be well-dispersed in the water, but the aqueous dispersion including the Clay-modified MWCNTs did not polymerize. The effects of the amount of MWCNTs and the flow rates of the continuous phase on the size had also been investigated.Process of the fabrication of the microreactor devices by laser cutting tool and ultra violet lithography had been searched. The results showed that the laser cutting tool was suitable for the preparation of microreactor with microchannel size over 100μm. In the thesis, we studied the possiblility of fabricating the microvalve made of the light-sensitive PNIPAm/Clay/MWCNTs has in situ in the microreactor cutted by the laser.