The effects of neutralization on the dynamic rheology of polyelectrolyte microgel mucilages

The dynamic rheological properties of a model poly(acrylic acid) microgel mucilage in the close‐packed concentrated region (reduced concentration cQ > 1) were evaluated as a function of the degree of neutralization, α = [NaOH]/[COOH]. As the parent microgel is neutralized, up to an order of magnitude increase is observed in the swelling ratio Q , dynamic modulus, and yield properties. Four regions were observed where the dynamic rheological properties exhibited a different power law dependence with increasing α. The dynamic yield strain does not change remarkably with increased neutralization, whereas the dynamic yield stress increases more than 10‐fold. This supports a mechanism where the yield strain depends on geometric considerations, whereas the yield stress reflects the stress required to force microgels past adjacent microgels. A linearity observed between modulus and dynamic yield stress with increased neutralization suggests a concerted expansion and affect on the rheological properties with the microgel core and emanating polymer chains. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012