Electrophoretic dynamic ultrasound scattering

Ultrasonic pulses are irradiated onto a concentrated suspension of microparticles, and the scattered waves of the moving particles are tracked in real time to measure their particle motion. A new methodology called Electrophoretic dynamic ultraSound Scattering (ESS) is proposed to apply DC or slow-period AC voltage to a particle suspension and to evaluate the electrophoretic velocity and zeta potential of the migrating particles in response. In this study, silica particles with a diameter of 2.5 μm were evaluated up to a concentration of 50 wt% using the newly proposed ESS method. A remarkable feature of the ESS method is that sample position dependence can be obtained in a single acquisition using pulsed ultrasound, without scanning through the sample in the depth direction as in the electrophoretic light scattering method. This makes it easy to perform measurements that take into account the so-called electroosmotic flow, in which the velocity decreases near the cell wall. In addition, since the electrophoretic velocity obtained from the phase of scattered field is obtained with its sign, the signed velocity, i.e., the positive or negative polarity of the particle charge, can also be identified. The validity of the obtained zeta potentials was verified by comparing them with the charge density of the particles obtained by titration. [Display omitted] •A method to evaluate sample position-dependent electrophoretic velocity was proposed.•From the signed velocity, the polarity of particle surface can also be determined.•Concentration dependence of the mobility up to 60 wt% concentration was realized.