UCST Responsive Microgels of Poly(acrylamide-acrylic acid) Copolymers: Structure and Viscoelastic Properties

Positive thermosensitive microgels were obtained via the inverse emulsion polymerization method with controlled feeding system. Random acrylamide and acrylic acid copolymer microgels with different compositions were synthesized and characterized. Dynamic light scattering was used to determine the hydrodynamic diameter and swelling behavior. The morphology, distribution, and size were determined by scanning electron microscopy (SEM). Cross-linker and acrylic acid concentration of the copolymer affected collapse temperature of the swelling behavior. An oscillatory rheometer was used to study the viscoelastic properties. The viscoelastic modulus G', and G '', of the microgel nanoparticle dispersions suggested a solidlike behavior. A scaling theory was applied to describe the structure of microgel dispersion, and the fractal dimension of the aggregates was obtained.