Effect of Radio-Frequency Fields on the Electrophoretic Mobility of Some Colloids

Abstract

Four sizes of polystyrene latex, starch grains, and gelatin‐coated polystyrene showed a voltage‐dependent, frequency‐specific response to radio‐frequency fields as a function of particle size. This response was a loss of negative surface charge irrespective of whether the initial surface charge was negative or positive. The charge returned to original values linearly with time over a period of hours, but returned to original values in 1 min if exposed to another frequency. At high concentrations of colloid (mean interparticle distance greater than 20 diam) no change in surface charge was apparent after exposure to an rf field. But dilution of this concentrated colloid without further exposure to rf reduced the surface charge to the value which it would have had if the diluted material had been exposed to rf. All these phenomena occurred irrespective of whether the colloids were in distilled water or in 10^—3 M NaCl.