see Figure and Experimental methods in the Supplementary Material for details). Control experiments showed that the fluorescein acted solely as a pH indicator for the solution and exhibited no preferential binding to the colloids (Figure ). Prior to application of the multimode electric potential the solution pH was constant at about 6.6. Upon first application of the multimode electric potential, the pH increased within seconds to about 7.1 and then decayed to 6.75 over 30 seconds. The pH dropped back to about 6.6 when the potential was removed. The pH near the cathode consistently reached a maximum of 7.1 -7.2 five seconds after applying the potential and subsequently declined to 6.7 -6.8 after 30 seconds for each potential application. (Figure ). Further increasing the steady potential to -200 mV effected nearly immediate separation of the colloids followed by assembly of colloidal crystals after about 35 seconds (𝐼 → 𝑆 → 𝐻) (Figure ). Finally, increasing the steady potential to -225 mV or above caused the particles to immediately and permanently separate, reaching a steady state separation after about 45 seconds (𝐼 → 𝑆) (Figure ). Interestingly, for steady potentials between -50 and -200 mV the steady potential determined the sequence of intermediate transient states visited by the colloids.