Study On The PH/Temperature Dual Stimuli Responsive Copolymer Microgels And Their Assambly To Form Fibers

The scale of smart hydrogel fibers is between the scale of smart block hydrogels and smart microgels, so the smart hydrogel fiber combined their advantages. They have not only the basic mechanical properties as materials that smart block hydrogel has, but also the large specific surface area and fast responsiveness to external stimuli of smart microgels. So they have potential applications in such fields as tissue engineering, separation filtration, enzyme or catalyst carrier, drug controlled release, etc. The smart hydrogel fibers were difficult to be prepared by traditional spinning methods because of their cross-linking structure. In this thesis, the smart hydrogels fibers were prepared by the assembly of pH and temperature dual stimuli responsive microgels in the ice crystal template. The ice crystal templating method is economical and environment-friendly, due to the nonuse of any organic solvent and additive, and no by-product, so the formed smart hydrogel fibers will be more suitable to be used in biomediccal field. The main research works and results obtained are as follows:(1)The pH/temperature dual stimuli responsive microgels were synthesized by emulsion polymerization in the reaction media with pH value of 4.0 and 7.0 based on N-isopropylacrylamide (NIPAM) and acrylic acid (AA) as comonomers, respectively. The measurement results obtained by proton magnetic resonance, element analysis and potential titration indicated that the AA unit content within the poly (NIPAM-co-AA) microgels synthesized under pH 4.0 condition was higher than the one under pH 7.0 conditions. The particle sizes of the microgels synthesized under pH 4.0 increased with the increase of AA monomer amount used, whereas the particle sizes of the microgels synthesized under pH 7.0 decreased with the increase of AA monomer amount used. The variation relationship of the hydrodynamic diameters of poly (NIPAM-co-AA) microgels as a function of temperature or pH of the aqueous media obtained by dynamic laser light scattering showed that, the microgels synthesized under pH 4.0 condition had more evident pH stimulus responsiveness and their temperature stimulus responsiveness was more dependent on the pH value of aqueous medium, revealing that the AA units were more homogeneously distributed inside the microgel polymer network.(2)The pH/temperature dual stimuli responsive microgels were synthesized by emulsion polymerization in the reaction media with pH value of 4.0 and 7.0 based on N-isopropylacrylamide (NIPAM) and methacrylic acid (MAA) as comonomers, respectively. The effect of pH value of reaction medium on the copolymerization behavior of NIPAM with MAA was studied. The differences in pH or temperature stimulus responsiveness between the microgels synthsised by the copolymerization of NIPAM with AA or MAA under the same pH condition were also investigated based on the results obtained in the first part. The results showed that the content of MAA units was higher than the one of AA units within the microgels, and the dependence of temperature stimulus responsiveness of poly (NIPAM-co-MAA) microgels on pH value of dispersion medium were obviously weaker than that of poly (NIPAM-co-AA) microgels.(3) The smart hydrogel fibers were prepared by the assembly of pH/ temperature dual stimuli responsive poly (NIPAM-co-AA) microgels in the ice-crystal template formed by unidirectional liquid nitrogen freezing method. Field emission scanning electron microscopy (FE-SEM) images indicated that the fibers were packed orderly by the microgels. The effect of the solid content and pH value of the microgel emulsion, the content of AA units within the microgels on production of the fibers were studied. The fibers were formed under 1 wt% solid content and pH 4.0 of poly (NIPAM-co-AA) microgel emulsion, and the network structure among fibers was produced as the content of AA units within the microgels was increased.