Motion of microgel particles under an external electric field

The influence of the swelling of charged microgel particles on their motion under an external electric field has been studied. The selected experimental observable was the electrophoretic mobility of the particles, which was measured as a function of the pH since its value controls the electrical charge of the particles. The mobility-pH curve presents a maximum and a minimum as a consequence of the competition between charge-density and friction coefficient variations during swelling. Ohshima's theory for polyelectrolyte-coated particles was employed, describing qualitatively the experimental results. Quantitative discrepancies suggest that charge renormalization should be considered.