Ultrasound attenuation and phase velocity of moderately concentrated silica suspensions

Ultrasound Study of Magnetic and Non-Magnetic Nanoparticle Agglomeration in High Viscous Media

Ultrasound attenuation spectroscopy has found wide application in the study of colloidal dispersions such as emulsions or suspensions. The main advantage of this technique is that it can be applied to relatively high concentration systems without sample preparation. In particular, the use of Epstein-Carhart-Allegra-Hawley's (ECAH) ultrasound scattering theory, along with experimental data of ultrasound velocity or attenuation, provide the method of estimation for the particle or droplet size from nanometers to millimeters. In this study, suspensions of magnetite and silica nanoparticles in high viscous media (i.e., castor oil) were characterized by ultrasound spectroscopy. Both theoretical and experimental results showed a significant difference in ultrasound attenuation coefficients between the suspensions of magnetite and silica nanoparticles. The fitting of theoretical model to experimental ultrasound spectra was used to determine the real size of objects suspended in a high viscous medium that differed from the size distributions provided by electron microscopy imaging. The ultrasound spectroscopy technique demonstrated a greater tendency of magnetic particles toward agglomeration when compared with silica particles whose sizes were obtained from the combination of experimental and theoretical ultrasonic data and were more consistent with the electron microscopy images.

Latex agglutination analysis by novel ultrasound scattering techniques

The latex agglutination test is employed to visualize antigen-antibody reactions through the aggregation of antibody-coated particles in the presence of an antigen. In the present study, we developed an ultrasound scattering technique to detect latex agglutination in an optically turbid media. However, the ultrasonic technique had less sensitivity to the dilute particle suspension than the optical techniques because of its wavelength. Therefore, we applied a time-correlation approach to detect small amounts of these aggregates using a sophisticated noise correction algorithm in the frequency domain. The lowest concentration of avidin used to detect aggregations of the biotin-coated particle using the ultrasound scattering technique was found to be 0.625 μg/ml. Furthermore, since the density differences between the particle and liquid were larger for silica suspensions than for polystyrene (PS) suspensions, a larger signal was proposed to be expected from silica suspensions. Nevertheless, it was found that latex agglutinations with the PS particle were more sensitive than those with the silica particles. The dynamic ultrasound scattering analysis along the sedimentation direction also supported the presence of strongly scattered intensity components of the PS aggregates, which is proposed to be due to the resonance scattering from PS spherical particles. Therefore, this technique can be employed to enhance scattering signals from particles for application in the agglutination test using ultrasound.

Interfacial structures of particle-stabilized emulsions examined by ultrasonic scattering analysis with a core-shell model

Pickering emulsions comprising liquid droplets stabilized by solid microparticles have gained much attention in the field of cosmetics, inks, and drug delivery systems. To ensure that microparticles in Pickering emulsions are localized at the surface of liquid droplets, ultrasonic spectroscopy analysis combined with scattering function theory was conducted in this study. Two specific cases were investigated: (1) silica particles and liquid droplets independently dispersed in liquid and (2) silica particles effectively localized at the surface of the droplets. It was found that the core-shell model was effective for analyzing nanoparticles anchored at the surface of oil droplets. Conversely, it was found that an effective shell comprised of solid particles was no longer observed as the particle size or the distance between solid particles increased. When a large solid particle was applied, the ultrasonic spectra resembled those of conventional surfactant-stabilized emulsions without solid stabilizers.

Measurement of Particle Concentration by Multifrequency Ultrasound Attenuation in Liquid-Solid Dispersion

In mineral transportations, it is essential to measure the gas hydrate particle concentration to manage the risk of flowline blockage. Traditional single-frequency ultrasonic methods measure the particle concentration by treating the mixtures with an average particle size, which ignores the influence of the particle size distribution, and thus, measurement accuracy is limited. Therefore, this research studies the multifrequency ultrasound attenuation method to measure the particle concentration through the prior estimate of particle size distribution. First, considering the large particle size and low-density contrast characteristics of the hydrate-water dispersion, the influence of multiple scattering among particles cannot be ignored apart from the scattering attenuation caused by each particle, so the ultrasonic scattering attenuation mechanism considering multiple scattering effects is established to solve the attenuation prediction problem of the hydrate-water dispersion. Since the solution of the equation obtained by the ultrasonic attenuation model produces a Fredholm integral equation of the first kind, an inversion algorithm combining simulated annealing with genetic algorithm based on ultrasonic attenuation mechanism is proposed to solve the ill-posed problem in the inversion calculation of particle concentration. Finally, considering the characteristics of hydrate-water dispersion, the experiments were carried out with millimeter-sized acrylic spheres and saltwater as substitute materials of the hydrate-water dispersion. The results show that the method based on the multifrequency attenuation of ultrasound in the range 1-5 MHz has a good discrimination for the particle size, and the measurement error of particle concentration is less than 3% under different particle size distributions.

Particle size distribution analysis of oil-in-water emulsions using static and dynamic ultrasound scattering techniques

Dynamic ultrasound scattering allows us to investigate the particle motion and its average size via the time-evolution analysis of the scattering amplitude in optically turbid media. Recently, we proposed a novel particle sizing method that simultaneously analyzes the depth dependences on the sedimentation velocity and the scattered intensity without prior knowledge about the shape of the size distribution (Ultrasonics, 65 (2016) 59-68). In this study, the applicability of the technique to Fluorinert/water dilute and concentrated emulsions (up to 40 vol%) was examined. For the bimodal distribution of the emulsion, the size distribution of the particles was successfully obtained by directly probing the particle motion with different sizes as a function of the sample depth. The validity of the analysis was also investigated by comparing with conventional ultrasonic spectroscopy.

Acoustic probing of the particle concentration in turbulent granular suspensions in air

Dilute gas-particle suspensions in which the particles are carried by the fluid are found in various industrial and geophysical contexts. One fundamental issue that limits our understanding of such systems is the difficulty to obtain information on the particle concentration inside these often optically opaque suspensions. To overcome this difficulty, we develop ultrasonic spectroscopy to monitor the local particle concentration [Formula: see text] of glass particles (with diameters [Formula: see text] 77 [Formula: see text]m or 155 [Formula: see text]m) suspended in air. First, we determine the minimal air velocity, [Formula: see text], necessary to suspend the particles from the maximum decrease in the transmitted wave amplitude and velocity of ultrasound propagating through the suspension. Next, setting the air velocity at [Formula: see text], we increase the mass of particles and monitor acoustically the local solid volume fraction, [Formula: see text], by measuring the ultrasound wave attenuation coefficient and phase velocity as a function of frequency on the basis of classical scattering and hydrodynamic models. For the frequency ranges and suspensions considered here, the viscous dissipation dominates over scattering and thermal conduction losses. We show that, for a characteristic air velocity [Formula: see text], the locally measured [Formula: see text] reaches a critical value, in agreement with a recent study on turbulent gas-particle mixtures. Moreover, we find that this critical [Formula: see text] increases with the size of the particles. Finally, analysis of the temporal fluctuations of the locally measured solid volume fraction, suggests that high density regions (clusters) are present even in suspensions with concentrations below the critical concentration. This differs from the current hypothesis according to which the critical concentration coincides with the onset of cluster formation.