MEASUREMENT OF MOBILITIES OF PARTICLES IN LIQUIDS BY OPTICAL AND ELECTRICAL TRANSIENTS

A new optical transient technique was developed to measure the mobilities of particles suspended in liquids. The optical method is based on the detection of light scattered from charged particles moving through a suspending medium under the influence of an external field. Sweepout and transient variants of this technique are outlined and a semiquantitative description of the optical signals is developed which permits the evaluation of the size, mobility, charge, and particle-substrate interactions, as well as estimates of the distributions of these quantities. Extensive testing of the method using dispersions of highly scattering charged particles in nonaqueous media was undertaken before applying the technique to other nonaqueous dispersions. Simultaneous measurements of the electrical transients showed that our currents were dominated by the excess ions in solution and that the charged particles contributed significantly to the current only at high particle concentration.