New developments in acoustic and electroacoustic spectroscopy for characterizing concentrated dispersions

There are two different techniques (acoustics and electroacoustics), both of which employ ultrasound instead of light for characterizing properties of liquid-based dispersions. Acoustic and electroacoustic techniques offer a unique opportunity to characterize concentrated dispersion in their natural states because ultrasound can propagate through samples that are not transparent for light. Elimination of a dilution step is crucial for an adequate characterization of liquid dispersions, especially when the high concentration leads to structured systems. The last 2 years have been very successful for these new techniques. We give a short overview of the new developments during this time. It includes first of all a new electroacoustic theory which is valid for concentrated dispersions. So far this theory works only for thin double layer but for any value of the Dukhin number. Acoustic theory has been expanded as well due to incorporation of the 'structural losses' in addition to the existing mechanisms of the particles interaction with the sound field. There is a version now which is supposed to work in the structured dispersions. We give here the first example of this new application for acoustics. Another important new application for acoustics is a 'mixed dispersions', which is dispersed system with several dispersed phases. A specially developed 'effective media' approach allows us to tackle successfully these very complicated systems. Hardware has been improved during last 2 years as well. We mention here just one new device: zeta -potential probe. It makes electrokinetic measurement very simple, fast (down to 15 s), precise (0.1 mv) and accurate. It can work on-line. We give here some examples of the results obtained with this probe. (C) 2001 Elsevier Science BN. All rights reserved.