Electrophoretic dynamic ultrasound scattering: Surface potential of particles in sedimenting particle suspensions using ultrasonic scattered phase

When ultrasonic waves are incident on a suspension containing particles in an electrical field, they produce scattered wave field that propagates inhomogeneously though the material. We have developed an ultrasonic method to analyze these propagating waves to determine the surface potential of the particles. This method is an acoustic version of electrophoretic light scattering and can be a method for determining zeta potential, which is considered a measure of the surface potential of particles. The advantage of this method is that it utilizes the phase of ultrasonic waves, which avoids sedimentation effects even for particles as large as several microns. The method utilizing this phase also allows identification of the sign of the surface charge and visualization of the flow gradient generated in the direction of sample depth. Taking advantage of the fact that it is an ultrasound, we were able to evaluate the zeta potential of silica particles with a concentration of about 40 vol%. The zeta potentials evaluated could be explained using one of the cell models, a theory of zeta potentials for concentrated materials.