Study Of PH/Temperature Dually Sensitive Microgels Based On Interpenetrating Polymer Network Structure

The intelligent microgels,which can respond to both pH and temperature change,have fascinating application outlook in many fields, such as intelligent drug release,sensor,biomass separation,etc..The pH/temperature dually sensitive microgels were previously prepared by random copolymerization method or core/shell structure method,in which the temperature sensitive component and the pH sensitive component interfered with each other.In this thesis,the pH/temperature dually sensitive microgels of interpenetrating polymer network(IPN) structure formed by temperature sensitive polymer network and pH sensitive polymer network were prepared,which did not have the drawback of the microgels produced by random copolymerization method and core/shell structure method.The rheological behavior of the pH/temperature dually sensitive microgel latexes exhibited that they had the thermo-thickening effect of great practical value.Finally,the fibers were produced through the assembly of the pH/temperature dually sensitive microgels in the ice crystal template formed by unidirectional freezing in liquid nitrogen.The main results obtained are as follows:(1) The microgels of IPN structure based on poly(N-isopropylacrylamide)(PNIPAM) and poly(acrylic acid)(PAA) (PNIPAM/PAA IPN microgels) were synthesized by seed-emulsion polymerization,using redox initiator at room temperature and the less crosslinked PNIPAM microgels as seeds.The microgels were determined to be composed of PNIPAM and PAA by Fourier transform infrared spectrometer(FTIR),and the IPN structure in the microgels was confirmed by transmission electron microscopy(TEM).The results obtained by dynamic laser light scattering(DLLS) showed that the microgels had good pH/temperature sensitivity without any marked interaction.(2) The effect of temperature on the viscosity of different concentration of PNIPAM/PAA IPN microgel latexes were investigated by rotation viscometer,and the results revealed that PNIPAM/PAA IPN microgel latex with higher PAA content had a greater thermo-thickening effect,even undergoing sol-gel transition at about 32@@@@.The mechanism of their thermo-thickening effect was discusse.In addition,the relationship between temperature and the storage modulus(G') and loss modulus(G") of PNIPAM/PAA IPN microgel latexes was investigated through the oscillation rheology experiments,and the structure change of the microgel latexes undergoing sol-gel transition was studied.(3) The assembly behavior of the PNIPAM/PAA IPN microgel in ice crystal template was investigated,and the results showed that the fibers were produced by unidirectional freezing of certain concentration of the microgel latex in liquid nitrogen.Field emission scanning electron microscopy images obtained under low accelerate voltage indicated that the fibers are composed of hexagonally packed PNIPAM/PAA IPN microgels.