The effects of pH and concentration on the rheology of Carbopol gels

Rheological measurements were performed on samples of highly cross-linked polymer microgels (Carbopols ETD 2050 and Ultrez 10), at various concentrations and pH values. Dramatic increases at low pH followed by broad peaks at intermediate pH in both yield stress and the elastic modulus were observed across all concentrations studied. We argue that this corresponds to the onset of jamming due to a rapid increase of volume fraction caused by the osmotic swelling of the polyelectrolyte microgel particles in the presence of NaOH. Differences were observed in the yield stress scaling behaviour between higher and lower concentration samples, which we believe to be indicative of a transition from a percolated structure at low concentrations, to a space filling network of compressed particles at high concentrations.