Novel strategy for the determination of UCST-like microgels network structure: effect on swelling behavior and rheology

Abstract

UCST-type interpenetrated and random copolymer microgels of polyacrylamide and poly(acrylic acid) were obtained via inverse emulsion polymerization method. The morphology of the microgels was determined by scanning electron microscopy (SEM) and atomic force microscopy (AFM). Dynamic light scattering was used to study both the swelling behavior as a function of temperature and pH and the particle size distribution of the system. Concerning the structural characterization, a combination of the equilibrium swelling theory (Peppas–Merrill equation) and AFM technique was used to determine the mesh size of microgels. An oscillatory rheometer was used to study the viscoelastic properties. The moduli, G′ and G′′, of the microgel dispersions suggested a solid-like behaviour and structure formation. Scaling theory was applied to describe the structure formation (clustering) and the fractal dimension. The influence of composition and type of microgel, random or interpenetrated, was discussed in the above mentioned properties and behaviors.