We describe two different techniques (acoustics and electroacoustics), both of which employ ultrasound instead of light for extracting information about the properties of liquid-based dispersions. Ultrasound can propagate through samples that are not transparent to light, which open up many new applications not possible with classical light scattering methods. Acoustic and electroacoustic techniques offer a unique opportunity to characterize concentrated dispersion, emulsions and microemulsions in their natural state, without any dilution.

Acoustic spectroscopy deals with measuring the attenuation of ultrasound within a certain frequency range. From this attenuation spectra we show that one can compute a particle size distribution from 10 nanometers to 100 microns.

Electroacoustic spectroscopy has two implementations depending on the driving force. We emphasize here the so-called Colloid Vibration Current (CVI), which is generated by the sound wave as it passes through the dispersion. From this electroacoustic signal we show that one can compute the zeta potential from which we can make important judgments about dispersion stability.

A brief review of the theoretical basis of acoustics and electroacoustics is given, with emphasis on concentrated systems. Recently, new theories have been developed for both acoustics and electroacoustics that allow us to include both particle-particle interactions as well as polydispersity in the theoretical model. Experimental evidence is presented that shows that this new approach is successful even in concentrated systems up to 45% by volume.

A variety of important applications for these acoustic and electroacoustic measurements are discussed in detail including: ceramics, mixed dispersed systems, chemical-mechanical polishing (CMP) abrasives, emulsions, microemulsions and latex materials.