Structure and Transport of Latex Microgels in Aqueous Suspension

Cationic latex microgel particles were studied in dilute aqueous suspensions of varying ionic strengths. Static light scattering indicates a Gaussian distribution of polymer density over the length scales probed. The measured radius of gyration is up to 50% larger than that obtained from TEM measurements of dried precursor particles. This radius of gyration is observed to be weak function of ionic strength. In contrast, dynamic light scattering measurements of the hydrodynamic radius showed a strong dependence on ionic strength, giving a ratio of the gyration to hydrodynamic radii from 0.53 at low ionic strength to 0.76 at high ionic strength. We interpret these data as an increased friction on the microgel particles due to electroviscous effects. While we draw a comparison of our measurements to existing theoretical results, there is at present no model to describe adequately these electroviscous effects for microgel particles.