Characterization of Concentrated Dispersions with Several Dispersed Phases by Means of Acoustic Spectroscopy

• Published in: Langmuir Vol. 16; no. 20; pp. 7597 - 7604
• Main Authors: Dukhin, Andrei S, Goetz, Philip J
• Format: Journal Article
• Language: English
• Published: American Chemical Society 03.10.2000
• ISSN: 0743-7463; 1520-5827
• DOI: 10.1021/la991600i

Acoustic attenuation spectroscopy can characterize the particle size distribution (PSD) of mixed concentrated dispersions, i.e., systems having more than one dispersed phase. In this paper, we will suggest two models that can be particularly helpful for describing such mixed dispersions. The first “multiphase” model assumes that we can represent the PSD of a real-world dispersion as a sum of separate log-normal distributions, one for each component in the mixed system. For this paper we assume that there are but two components, which reduces the overall PSD to a simple bimodal distribution. The second “effective medium” model further assumes that one needs to determine the PSD of just one component in an otherwise complex mixed system. All other disperse phases are lumped together into an effective homogeneous medium characterized by some composite density, viscosity and acoustic properties. By adopting this viewpoint, we significantly reduce a complex real-world mixture to a simpler dispersion of a single pre-selected dispersed phase in a newly defined “effective medium”. We need not even define the exact nature and composition of this new medium since we can simply measure, or perhaps calculate, the required composite density, viscosity, attenuation, and sound speed. The “multiphase” model is most suitable for samples where it is desired to measure the PSD for more than one well-characterized disperse phase. In contrast, the effective medium model is particularly useful where it is desired to measure only one component in a complex poorly defined multicomponent mixture. Experimental results are presented for five different mixtures including alumina, zirconia, silica, and calcium carbonate materials. These tests demonstrate that the mathematical complexity of the “multiphase” model often leads to the familiar “multiple solution problem” whereas the “effective medium” approach is more reliable and robust. Furthermore, the “verification” approach reveals an aggregation phenomena in the PCC−silica mixed dispersion.