Carbon black, electrophoretic mobility

These effects can be illustrated more quantitatively. The drop in the magnitude of the potential of mica with increasing salt is illustrated in Fig. V-7 here yp is reduced in the immobile layer by ion adsorption and specific ion effects are evident. In Fig. V-8, the pH is potential determining and alters the electrophoretic mobility. Carbon blacks are industrially important materials having various acid-base surface impurities depending on their source and heat treatment. 

Fig. V-8. Electrophoretic mobility of carbon black dispersions in 10 KNO3 as a function of pH. (From Ref. 93.)...

Initial studies were made with the Rank Bros, electrophoresis unit, using the dilute supernatant suspension over a dispersion of 3.33g of carbon black per liter of dodecane equilibrated for 24 hours with the added 0L0A-1200. The electrophoretic mobility (u) of 1-3 pm clumps of particles was observed at a field of 100 volts per centimeter. The zeta-potentials ( ) were calculated... 

Figure 3.5 Electrophoretic mobility u of carbon black in solutions of different surfactants at 308 K (reproduced with permission [5]).

FIG. 4 Electrophoretic mobility vs. pH for a range of amphoteric solids, including alumina [777], a furnace carbon black [56] and chemically modilied carbon blacks and activated carbons [82],... 

Of course, surface charge development has been well documented in the carbon black literature [36, where particle coagulation is the key issue. Thus, for example. Kratohvil and Matijevic [56] measured electrophoretic mobilities and concluded (without alluding to the work of Frampton and Gortner) that [c]arbon particles carry a positive charge at lower pH values." They also studied the pH dependence of the adsorption of a nonionic and an anionic surfactant as well as of electrolytes with counterions of varying charges. 

FIG. 25 Electrophoretic mobility (pm/s per V/cm) vs. pH for a series of chemically modified and weathered carbon blacks. (Adapted from Ref. 70.)... 

Experimental. Samples for electrophoretic mobility (EM) measurements were prepared as previously described for the titration experiments except that violent mixing with destruction of carbon agglomerates was desirable here and was promoted with a 5-10 minute treatment of the capped serum bottles in an ultrasonic bath. The indicator was, of course, deleted in the EM sample preparation procedure. Following mixing, a few drops of the mixture was transferred to a 25 ml flask of benzene and given another ultrasonic treatment. This procedure produced a fairly stable colloid suspension of the carbon black which was used to fill the glass-Teflon commercially available EM cell manufactured by Zeta-Meter, Inc. 

---