Contributions of particles to electrical conductivity of colloids

A new method was developed which permits transient and background electrical conductivity measurements on supernatants and colloids with variable concentration of particles in the same cell. The method was applied to two nonaqueous titanium dioxide-xylene dispersions, one with a physisorbed charge control agent (cca) and another with a chemically attached stabilizer and cca. At particle volume fractions 0.01-0.1, the dispersions have electrical transient conductivities similar to those of the supernatants, but with measurable contribution by charged particles to the transient conduction. This agrees with estimates based on measured particle mobilities and sizes. The background conductivities increase rapidly with particle concentration and at maximum concentrations the dispersion conductivities exceed supernatant conductivities by two to three orders of magnitude. Background conductivity increases might be due to charge injection enhanced by electric field focusing by particles which have higher permittivity than the medium and to conduction along particle surfaces. © 1986.