Novel smart pH-sensitive copolymeric hydrogels have been synthesized by inverse microemulsion polymerization of p-nitro phenol acrylate (NPA) and N-isopropylacrylamide (NIPA) using Aerosol (AOT) as a surfactant and ethylene glycol dimethacrylate (EGDMA) as a crosslinking agent. The polymerization reaction was performed in presence of an oil-soluble salt to reduce the dimensions of the micellar diameter. The average particle diameter and the particle size distribution of the nanogels were measured in acetone at 25 degrees C by quasielastic light scattering (QLS) showing average diameter of 33 mm. The nanogels were characterized by FTIR-ATR, H-1 NMR, UV-vis spectroscopy and DSC. These nanoparticles had shown a selective swelling-collapse response to external pH changes. (C) 2008 Published by Elsevier B.V.