The determination of shape, size, and size distribution of charged particles in solution by evaluation of the electrical anisotropy effect

Abstract

The anisotropy effect of the electrical conductivity occurs in solutions of anisometric polyelectrolytes under the influence of the orienting forces of a velocity gradient. A Couette-type apparatus for the generation of velocity gradients up to 20,000 sec. −1 is described which permits measurements of the conductivity in three orthogonal directions. Evaluation of the curves obtained yields shape, size, and stability of the particles. A convenient method for the evaluation on the basis of Schwarz' theory (1, 2) is presented. Furthermore, the size of the particles may be calculated from the relaxation of the conductivity changes after the flow is stopped. The theory is extended to relaxation processes of nonuniform particles, and a method for the evaluation of the relaxation curves is developed which yields the average size and the size distribution of the particle assembly. The range of application of the flow method and the relaxation method is discussed; both methods may be applied to charged particles in the size range between 10 −5 and 10 −2 cm. The application is demonstrated on rod-shaped and disc-shaped polyelectrolytes (sodium thymonucleinate and graphitic acid, respectively), and the results are found to be in agreement with electron microscope determinations. The methods proved to be useful for the investigation of the micellar state of amphiphilic substances in solution.