On the electrophoretic mobility of isolated colloidal spheres

We studied the electrophoretic mobility μ 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 μ was observed to be independent of particle size and surface chemistry. Corresponding effective charges Zμ*, however, scaled with the ratio of particle size to Bjerrum length λB: Zμ* = Aa/λB with a coefficient . Our results are discussed in comparison to other charge determination experiments and charge renormalization theory and with respect to the issue of charge polydispersity.