An ultrasound velocity and attenuation scanner for viewing the temporal evolution of a dispersed phase in fluids

Ultrasound scanning using the group velocity of sound to determine the concentration of a liquid or solid phase dispersed in a fluid has been used for many years to characterize dispersions with regard to their long-term stability. The technique has the twin advantages of speed and operation in concentrated, optically opaque dispersions. In this work, the group velocity technique is combined in a single instrument with phase velocity and attenuation spectroscopy measurements to give valuable additional information about particle size and the microscopic particle distribution, related to important destabilization phenomena such as particle flocculation. This provides earlier evidence of the processes that finally lead to gravitational destabilization and reduced shelf life of fluid dispersions such as emulsions. A further advantage is the ability to compare the measured spatial and temporal variation with computer models. The technique works in optically opaque materials and in concentrated colloids, giving a quantitative picture of the macroscopic spatial distribution of the dispersed phase and a semiquantitative picture of microscopic particle aggregation processes. Since these microscopic particle rearrangements are often responsible for the ultimate gravitational destabilization of colloidal systems, the Acoustiscan, as we have called the ultrasonic scanner described herein, may indicate product instability long in advance of visual evidence. New data are presented for protein containing sunflower oil-in-water emulsions, destabilized with Tween 20, in order to exemplify the use of the Acoustiscan for the characterization of food emulsions. The Acoustiscan instrument provides quantitative information about the destabilization of emulsions,dispersions, and colloidal systems in a rapid and informative manner. It simultaneously measures changes in the dispersed phase and follows microscopic changes in the arrangement of particles. The instrument has many other uses, for example, for characterizing crude oil, pharmaceuticals, cosmetics, and agrochemicals. It can also be used to follow crystallization processes. It does all this in materials over an extremely wide concentration range, from a few percent up to the highest concentrations obtainable. Moreover, when data are compared with computer models, it is possible to infer the presence of gels whose yield stress is far lower than any measurable by contemporary rheological equipment. This makes the Acoustiscan ideal for the study of the new soft solid materials currently in development.