Acoustic and electroacoustic spectroscopy

Two new ultrasound based techniques (acoustics and electroacoustics) offer a unique opportunity to characterize concentrated dispersion, emulsions and microemulsions in their natural state, without dilution. Elimination of the dilution protocol is crucial for an adequate characterization of liquid dispersions, especially structured. Dilution changes the thermodynamic equilibrium in these systems and affects their reological properties. Changes in equilibrium conditions can lead to variation of the particle size and can also affect surface chemistry. In this paper, a short review of the theoretical basis of the ultrasound techniques is given. Emphasis is placed on the theoretical models which are supposed to be valid in concentrated systems. These theories have been developed recently on the basis of 'cell model concept' for both acoustics and electroacoustics. This approach opens the way to implement particle-particle interaction into the theoretical model. Experiment proves that these theories are adequate in concentrated systems up to 45% vol. Second part of the paper is dedicated to the applications of acoustics; and electroacoustics. The list of applications includes: ceramics, mixed dispersed systems, chemical-polishing materials, emulsions, food emulsions, microemulsions and latecies. (C) 2000 Elsevier Science B.V. All rights reserved.