Evidence for charge regulation in the sedimentation of charged colloids

Recent experimental data for the centrifugal sedimentation-diffusion profile of charged colloidal silica (diam ∼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 φ (>0.1 vol%) with the data much better reproduced when charge regulation is included. (letter to the editor)