Temperature Dependence of Electrophoretic Mobility and Hydrodynamic Radius of Microgels of Poly(N-isopropylacrylamide)

Electrostatic interactions in charged microgels, which are dominated by the microgel net charge, play a crucial role in colloidal stabilization and loading of small, charged molecules. In this study, the temperature dependences of electrophoretic mobility mu and hydrodynamic radius R-h were measured for a slightly ionized poly(N-isopropylacrylamide) (PNIPA) microgel in a dilute suspension. A decrease in R-h was observed in the temperature range between 30 degrees C and 35 degrees C, corresponding to the lower critical solution temperature of PNIPA, and an increase in vertical bar mu vertical bar was observed in a higher temperature range between 34 degrees C and 37 degrees C. The analysis based on electrophoresis theory for spherical polyelectrolytes indicated that the net charge of the microgel decreased as the microgel was deswollen.