Volume phase transition temperature tuning and investigation of the swelling-deswelling oscillation of responsive microgels

Temperature- and pH-responsive polyampholyte microgels were prepared by an aqueous dispersion polymerization. Scanning electron microscopy and dynamic laser light scattering (DLS) were employed for the characterization of the morphology and size distribution of the microgels. Temperature- and pH-dependent volume phase transitions of the polyampholyte microgels were also investigated using DLS. The microgels showed an interesting swelling-deswelling oscillatory behavior when the pH was varied. An interpretation was proposed for the phenomenon in terms of Coulombic repulsion and hydrophobic hydration. It is of great interest that the volume phase transition temperature (VPTT) of the polyampholyte microgels can be varied by changing the pH. This could be a convenient approach for tuning the VPTT of N-isopropylacrylamide-based hydrogels. (c) 2007 Society of Chemical Industry.