Charge controlled swelling of microgel particles

The swelling of cationic microgel particles has been studied experimentally , in the weak screening regime. The solution pH was selected as the externa l variable triggering the swelling, which was followed by dynamic light sca ttering. The particle charge was determined by conductometric and potentiom etric titrations, leading to a good correlation between the charge of the m icrogel network and its size. This leads to the conclusion that the swellin g is mainly charge controlled. The Flory-Huggins thermodynamic theory for g els, including a term accounting for the counterion distribution within the microgel, has been used to interpret the experimental data. The osmotic te rm associated with the counterions explains fairly well the observed behavi or, and additional contributions due to the internal microgel microscopic s tructure are not necessary, as Pincus et al. have suggested.