ELECTROACOUSTIC DETERMINATION OF PARTICLE-SIZE AND ZETA-POTENTIAL

When an alternating voltage is applied to a colloid, the particles mov e back and forth at a velocity that depends on their size and zeta pot ential and on the frequency of the applied held. As they move, the par ticles generate sound waves. In this paper we describe a new device fo r measuring this electroacoustic effect, From this measurement the fre quency-dependent electrophoretic mobility (or ''dynamic'' mobility) of the particles can be determined in suspensions of arbitrary concentra tion, and from the dynamic mobility spectrum it is possible to obtain the size distribution and the zeta potential of the particles. The gre at advantage of the technique is that it is not limited to dilute susp ensions. After describing the operating principles and calibration of the device, we present mobility spectra obtained on model silica suspe nsions. It is found that these spectra are in good agreement with O'Br ien's thin double layer formula, down to a kappa alpha value of 20. We then show how size distribution and zeta potential can be obtained fr om the mobility spectrum, and we compare results for a number of suspe nsions with measurements made using other techniques. (C) 1995 Academi c Press, Inc.