The Litsesizer 500 (Anton Paar, Graz, Austria) was used to determine the electrophoretic mobility, μe, by phase analysis of the light scattering by the sample. The wavelength of the laser was 658 nm, the laser power was 40 mW, and the scattering angle was either 15° or 175°, optimized automatically through the build-in algorithm of the device. The temperature was 25