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Surface charging of polystyrene latex particles stabilized with sodium dodecyl sulfate (SDS) was investigated. The surfactant adsorption isotherm and electrophoretic mobilities of monodisperse latex particles were measured. Electrophoretic mobility measurements at moderate ionic strengths (around 0.1 M) indicated a substantial degree of counterion binding to adsorbed dodecyl sulfate anions, comparable to that found in SDS micelles. We offer a consistent description of surface charging of SDS-stabilized latex particles and SDS micelles taking into account binding of sodium counterions to dodecyl sulfate anions.

The ECAH theory, named after the successive works of Epstein and Carhart and Allegra and Hawley, is a very powerful tool that allows the estimation of the particle size distribution in diluted dispersions from ultrasonic attenuation measurements. However, in the case of low-density contrast systems such as polymer latexes, discrepancies have been reported by various authors between the predicted and experimental data at the lower frequencies (below 20 MHz). To elucidate the reasons for such a mismatch, the role of the intrinsic attenuation of the polymer is investigated in this work. A new method for measuring the intrinsic attenuations using a commercial unit is developed and applied to polystyrene in the frequency range 1−120 MHz. A linear relationship between the sound attenuation and the frequency is obtained, which differs significantly from the previous data in the literature. With the use of these values for the intrinsic attenuation, it has been found that the predictions of the attenuation spectra in polystyrene latexes given by the ECAH model are in good agreement with the experimental data.

This paper presents theoretical approaches for the acoustic analysis of concentrated suspensions and emulsions. The aim is an extension of the well-established single-particle theory of Epstein, Carhart, Allegra, and Hawley (ECAH), by introducing effective ways of accounting for the effect of interacting neighboring particles. After discussion of three modeling approaches and their implementation into the general ECAH framework, and demonstration of their effect on the acoustic field, the behavior of each thus defined model is analyzed as a function of particle concentration. In all cases, convergence to the well-established ECAH result is observed in the dilute limit. At high concentrations, particularly good behavior is found for a core−shell (pseudofluid) model, both for suspensions and emulsions. This model correctly predicts an increase of attenuation with particle concentration which is less than linear, in agreement with experimental observations.

In the first part of this work, a core−shell extension of the isolated-particle framework of Epstein, Carhart, Allegra, and Hawley (ECAH theory) has been developed for the simulation of sound attenuation in concentrated emulsions and suspensions. In the present paper, the model predictions are validated by comparison with a systematic set of experimental data. The systems under consideration include silica/water, poly(tetrafluoroethylene) (PTFE)/water, and corn oil/water at a range of particle sizes, particle volume fractions, and frequencies. These data cover a wide variety of situations where energy dissipation is dominated by viscoinertial losses, thermal losses, or combinations thereof, thus providing a significant test for the reliability and generality of the model. Moreover, the potential of the model as a basis for the estimation of particle sizes from acoustic data is investigated.

In this paper, the use of ultrasonics for the determination of particle size distributions (PSDs) in suspensions and emulsions is discussed. Focusing on systems with a large density difference between the dispersed and continuous phases, a mathematical model is used to correlate the primary measurement&sbd;the attenuation of acoustic waves as a function of frequency&sbd;to the PSD, and it becomes clear that the quality of the PSD thus obtained is directly related to the accuracy of the model parameters. To overcome possible problems in the case of incomplete physical-property information, we have developed a generalized procedure for particle sizing, based on a parametric sensitivity analysis and parameter calibration. The latter allows for computation of physical properties from acoustic data provided that the PSD is known. Moreover, particle sizing results are presented for dispersions of different sizes and materials, and compared to the findings of electron microscopy and dynamic light scattering.