Mini-Encyclopedia of Papermaking Wet-End
Part Two: Definitions and Concepts
Microelectrophoresis is the best-known method for determination of zeta potentials of fiber fines and filler particles in paper machine white water. The apparatus includes a capillary cell, two chambers that include electrodes, and a means of observing the motion of particles. Because the capillary diameter is usually smaller than the length of a cellulosic fiber, these may be removed by filtration through a screen before the test. The apparatus is filled with very dilute suspension and the chambers are closed. A direct-current voltage is applied between electrodes in the respective chambers. One uses a microscope to determine the velocity of particles. The ratio or the velocity to the electrical field strength is known as the electrophoretic mobility. By making reasonable assumptions about the size of the observed particles and the electrical conductivity it is possible to calculate the value of the zeta potential. Zeta potential values near to zero indicate that the particles in the mixture are likely to stick together when they collide, unless they also are stabilized by non-electrical factors. Particles having a negative zeta potential are expected to interact strongly with cationic additives.
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