| The carbon black and diesel soot particles formed stable colloidal suspensions when dispersed in water. Although not necessarily representative of
those suspensions formed in n-dodecane, such suspensions do enable aqueous electrophoresis studies to be conducted. The variation of both zeta
potential and intensity-average particle diameter with solution pH for both colloidal substrates is shown in Figure 2. Carbon black aggregates are
highly anionic (−30 to −45 mV) between pH 6 and pH 11. Below pH 6, the gradual reduction in surface charge leads to their progressive aggregation,
from an initial characteristic sphere-equivalent diameter of 200 nm in alkaline media to flocs of more than 800 nm at an isoelectric point (IEP) of
approximately pH 4.2 and micron-sized aggregates with appreciable cationic surface charge at pH 2–3. The diesel soot particles exhibit broadly
similar behavior, but with some subtle differences. The aggregates formed in alkaline media are somewhat larger, with sphere-equivalent diameters of
400–440 nm and zeta potentials of around −40 mV; they remain more or less stable from pH 11 to around pH 4, with an isoelectric point at
approximately pH 3. Micron-sized aggregates are formed between pH 2 and pH 3. |
but probably not.