Rheological properties of water swellable microgel polymerized in a confined space

The rheological properties of a water swellable microgel polymerized in an inversed micelle, confined space, were studied. The chemical component of the microgel was poly(dimethylacrylamide-co-2-acrylamide-2-methyl-1-propanesulfonic acid) crosslinked with methylene-bis-acrylamide. The flow curves of the microgel aqueous dispersion containing sodium chloride (3 mmol/L) were analyzed using the Herschel-Bulkley equation. Since the overlap concentration (c*) of the microgel was precisely agreed with 1/[η], the microgel particle is likely to be dispersed as an impenetrable particle in the dilute regime according to the Einstein's law. The microgel aqueous dispersion showed the viscoelastic-liquid like behavior in a higher concentration above c*. There was a critical concentration that the apparent yield stress appeared. The effective volume fraction occupied by the microgel particle was 0.7 at the critical concentration. To investigate the mechanical properties of such a concentrated sample, steady state compliance (Je0) of the microgel dispersion was evaluated by the creep recovery measurement. The relationship between Je0−1 and the concentration in semi-dilute regime was according to a scaling law. Moreover, the microgel dispersion behaved as if a bulkgel when its concentration was sufficient high. It is considered that the discrete microgel particles would be close packed, resulting deformed and deswollen the particles, and it seemed that the discrete gel networks were stuck each other as if the microgel dispersion turned to a continuous gel.