On the electrophoretic mobility of isolated colloidal spheres

We studied the electrophoretic mobility it of highly charged colloidal spheres in very dilute low salt aqueous suspension. We combined experiments on individual particles and ensemble averaged measurements. In both cases it was observed to be independent of particle size and surface chemistry. Corresponding effective charges Z(mu)*, however, scaled with the ratio of particle size to Bjerrum length lambda(B): Z(mu)* Aa/lambdaB with a coefficient A approximate to 2. Our results are discussed in comparison to other charge determination experiments and charge renormalization theory and with respect to the issue of charge polydispersity.