Rheological study of aqueous dispersions of in situ gelable thermosensitive polymer nanogels

Thermosensitive poly(N‐isopropylacrylamide‐co‐acrylamide) nanogels with varied monomer compositions were prepared by precipitation polymerization. The aqueous dispersions of these thermosensitive nanogels (9 wt% of nanogel particles in phosphate‐buffered saline solution) exhibited in situ gelable characteristics. A steady‐state and dynamic rheological analysis demonstrated that the nanogel dispersions were typical pseudoplastic liquids at room temperature. The viscosity of the nanogel dispersions at a constant shear rate increased with an increase of the acrylamide content. When the temperature was increased to 37°C, the pseudoplastic liquid turned into an elastic solid, as the result of a sol–gel phase transition of the nanogel aqueous dispersion during the raise of the temperature. Dynamic temperature ramp circle curves suggest that the sol–gel transition was reversible but with a clear hysteresis. POLYM. ENG. SCI., 2009.