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 µ 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^◦ C and 35^◦ C, corresponding to the lower critical solution temperature of PNIPA, and an increase in |µ| was observed in a higher temperature range between 34^◦ C and 37^◦ C. The analysis based on electrophoresis theory for spherical polyelectrolytes indicated that the net charge of the microgel decreased as the microgel was deswollen.