The Colloidal Dynamics Acoustosizer uses the Electrokinetic Sonic Amplitude (ESA) effect. Charged particles in suspension are forced to move by an oscillating electric field to produce acoustic compression waves (i.e., sound waves at the frequency of the excitation). Changes in density as the particles move towards and away from the electrodes generate acoustic waves at the surface of the electrodes as an echo of the excitation. The amplitude of the acoustic response is proportional to the velocity of the particle caused by the electric field. The velocity is proportional to the electric field amplitude. The "constant" of proportionality is the dynamic mobility, which can be shown to be a function of particle size, zeta potential, frequency, and phase lag of the particles velocity relative to the excitation frequency. This relationship is used to extract the particle size and surface charge (zeta potential) from measurement of the ESA. The advantage of this technique is that it can be applied to very concentrated suspensions (up to 40 vol%). The particle size range that can be measured by this technique is approximately 0.02 mm to 10 mm. This instrument measures the charge associated with the surface (zeta potential) and the size distribution of the particles simultaneously. Single samples of as small as 20 mL can be measured, as well as continuous monitoring of colloidal processes.

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