According to Smoluchowski’s and Komagata’s theory, the electroosmotic and electrophoretic velocities vary with the depth of cell such that the distribution of velocities must be represented by a symmetrical parabola. However, in practical measurements of the electrophoretic velocities of sedimentary particles such as pulp fines and fillers, the distribution curve of velocities was found to be asymmetrical about the cell center. Thus use of the conventional method often gives rise to a serious error. The reasons for this are discussed and an improved method is proposed.
The time-dependent changes in zeta potentials (ZP) of clay and monodispersed polystyrene latex with added polyethyleneimine (PEI) or cationic polyacrylamide were investigated by the improved method. For instance, the ZP of clay, which was -42 mV originally, became +9 mV just after addition of PEI at a level of 0.1 % on clay, decreased rapidly at an initial stage, became -13 mV after
1 hr and finally reached -17mV. The rate of change in ZP varied widely with the degree of agitation, the addition level of polymer, the molecular weight and so on. The highest difference between initial and final ZP we have obtained hitherto is over 50mV. These phenomena must be closely related to the conformational change of polymers sorbed on solid surface and will offer important and fundamental information on how to use polymer additives in papermaking.