A METHOD TO MEASURE THE AVERAGE CHARGE TO MASS RATIO OF PARTICLES IN LOW-CONDUCTIVITY MEDIA

The average charge to mass ratio of suspended particles is an electrical characteristic which can be related to surface charge density or zeta-potential. A new method to measure the average charge per unit mass of particles dispersed in low-conductivity media is proposed. The method depends on the ability of a flow of an insulating liquid to separate the electric double layers from around charged particles held stationary on a porous support. The countercharges are collected in a Faraday cup and the total is charge measured. The charge on the particles is equal to but opposite in sign to the collected charge. The average charge to mass ratio of the particles is the ratio of the total particle charge to the mass of particles. When a sample of dispersion with a known mass of particles is used, the only measured quantity is the charge collected in the Faraday cup. The reasonableness of the method is demonstrated with carbon black particles suspended in dodecane and charged with various concentrations of Chevron's OLOA 1200.