On multiple-particle effects in the acoustic characterization of colloidal dispersions

Acoustic spectroscopy is a relatively recent method for the characterization of suspensions and emulsions. Measurement of the attenuation of ultrasonic waves is often the first step of such analyses. Coupled with appropriate theoretical models, these data allow one to infer information such as particle size distribution and particle concentration. Several of such models are available, describing the behaviour of isolated particles. However, the validity of the isolated-particle assumption is limited to low particle concentrations, where nonlinear multiple-particle effects are negligible. To investigate this aspect, this paper is concerned with the multiple-particle effects as they arise in concentrated colloidal dispersions of high density contrast between the phases. The mechanism of multiple lossless scattering is demonstrated to be of minor influence in these systems. This suggests the presence of another multiple-particle effect, namely particle-particle interactions in the dissipative energy absorption.