Evidence for charge regulation in the sedimentation of charged colloids

Recent experimental data for the centrifugal sedimentation-diffusion profile of charged colloidal silica (phi similar to 44 nm) in ethanol is analysed based on local charge neutrality and by either assuming a fixed particle charge or incorporating charge regulation. Especially at a high Debye length ( > 30 nm) the two models deviate at higher particle volume fractions phi ( > 0.1 vol%) with the data much better reproduced when charge regulation is included.