Research Of Dual Sensitive Poly( N-isopropylacrylamide) Copolymer Nanogels

Environmental-responsive nanogels were widely used in synthesis of nanomaterials, drug delivery systems, cosmetics and so on. Two kinds of thermo- and pH sensitive nanogels, p(NIPAM-co-SD) and p(NIPAM-co-AM) with mono-dispersive property, were synthesized by emulsifier-free polymerization using N-isopropylacrylamide(NIPAM) as thermo-monomer, methacrylate acylation sulfadiazine(SD) and allylamine(AM) as pH sensitive monomers. The nanogels were characterized by DLS and TEM to investigate their average size and size distribution in aqueous solution at different temperature, pH and ion intensity. Additionally, the nanogels were further used to stabilize Pickering emulsion and the staibilization mechanism was explored.1) p(NIPAM-co-SD): (1) their average size was decreased with the increase of temperature, and its volume transition temperature ranged from 33.0℃to 34.0℃. When nanogels were dispersed in 0.05～0.8 mol/L sodium chloride aqueous dispersion, the average size was about 200 nm and it became much smaller than that without sodium chloride existence. (2) when pH was increased from 6.00 to 7.40, the nanogel size at 25.0℃was increased because of the increase of their ionization degree. However, their size was increased with the pH decrease from 6.00 to 1.50. (3) The nanogels were found to be spherical and the internal morphology was influenced by monomer mole ratios by TEM characterization;2) p(NIPAM-co-AM): (1) their average size was decreased with increase of temperature. The nanogel size was decreased with pH increase from 6.00 to 7.40, and was increased when pH of nanogel aqueous dispersion was increased from 4.00 to 6.00; (2) TEM imaging showed that these nanogels are mono-dispersive spherical structure at 25.0℃.3) Pickering emulsion was prepared using nanogels. The size of the Pickering emulsion could be varied from 100 nm to several micrometers by controlling the preparation process and formulations. Pickering emulsions were characterized using TEM, optical imaging, and fluorescence imaging. The thermo- and pH sensitivity, and stability were also investigated. In addition, stabilization mechanism of these nanoscale emulsions was explored using destruction of hydrogen bonds experiment, etc.