Ultrasonic Attenuation Spectra Research Articles

Ultrasonic Propagation in Highly Concentrated Oil-in-Water Emulsions

The dependence of the ultrasonic attenuation spectra (0.4−160 MHz) of n-hexadecane oil-in-water emulsions on droplet concentration (1−92 vol %) was measured. In dilute emulsions the attenuation coefficient increased with droplet concentration, but in concentrated emulsions it decreased. Traditional multiple scattering theory (Allegra and Hawley−Waterman and Truell) greatly overestimated the attenuation, even at moderate concentrations (>10%), because it ignores thermal overlap effects. On the other hand, an extended multiple scattering theory that takes these effects into account gives good agreement with experimental measurements up to much higher droplet concentrations (50−70%). Neither theory could be used to accurately predict the ultrasonic properties of highly concentrated emulsions (>90%)

Ultrasonic spectroscopy study of relaxation and scattering in whey protein solutions

Ultrasonic attenuation spectroscopy was used to investigate the influence of pH on fast chemical reactions and aggregation of whey proteins in aqueous solution. Ultrasonic attenuation spectra (1–100 MHz) of 2.5 wt% aqueous solutions containing either ‘native’ or ‘alkali-denatured’ proteins were measured as a function of pH (2–12). Peaks in the attenuation occurred at pH 2.8 and 11.6 due to proton transfer equilibria, ie CO2H ↔ CO2− + H+ and NH2 + H+ ↔ NH3+ respectively. Attenuation at other pH values was attributed to a hydration relaxation mechanism. Relaxation times for the equilibria were of the order of 10−8 s. There was an additional attenuation peak at the isoelectric point of the proteins (pH 5) for solutions containing ‘alkali-denatured’ protein, which was due to scattering of ultrasound by aggregated proteins. The particle size distribution of the aggregates could be determined using ultrasonic scattering theory to analyse the attenuation spectra. Ultrasonic spectroscopy is an extremely valuable tool for probing the molecular characteristics of proteins in solution. © 1999 Society of Chemical Industry

Ostwald Ripening of Hydrocarbon Emulsion Droplets in Surfactant Solutions

Ultrasonic attenuation spectra (1−150 MHz) of a series of 5 wt % oil-in-water emulsions containing hydrocarbon droplets (n-decane, n-dodecane, n-tetradecane, n-hexadecane, n-octadecane) stabilized by various surfactants (Brij 35, Tween 20, SDS, Triton X-100) were measured as a function of time. Droplet size distributions were calculated from attenuation spectra using ultrasonic scattering theory. Changes in droplet size distribution were also measured by static light scattering on the same emulsions after dilution (<0.01 wt %). Ostwald ripening rates were determined from the time-dependence of the mean droplet size using the Lifshitz−Slyozov−Wagner theory. Ultrasonic spectroscopy was more sensitive to small changes in droplet size than light scattering and could be used to analyze emulsions containing smaller droplets (d < 100 nm). Ripening rates decreased exponentially as the molar volume of hydrocarbon increased. They also depended on the type of surfactant used to stabilize the emulsions, decreasing in the following order: Brij 35 > Tween 20, Triton X-100 > SDS. The addition of excess surfactant (0.5−5 wt % Tween 20) to n-tetradecane emulsions stabilized by Tween 20 had little influence on ripening rates.

Influence of visco-inertial effects on the ultrasonic properties of monodisperse silica suspensions

The measured ultrasonic velocity and attenuation spectra (0.5–150 MHz) of colloidal suspensions containing monodisperse silica particles (φ=5%, r=190 nm) dispersed in a series of water–glycerol mixtures (0% to 80% glycerol) were in good agreement with predictions of multiple scattering theory. The major cause of excess attenuation and velocity dispersion was visco-inertial dissipation losses, which arose because of the density contrast between the silica particles and surrounding liquid. There was a maximum in the attenuation spectra that decreased in height and shifted to higher frequencies as the glycerol concentration was increased because of the reduction in density contrast and increase in continuous phase viscosity (1 to 60 mPa.s). These results suggest that ultrasound could be used to measure continuous phase viscosities in colloidal suspensions.

Ultrasonic attenuation spectroscopy study of flocculation in protein stabilized emulsions

The extent and kinetics of droplet flocculation in emulsions was studied using ultrasonic attenuation spectroscopy. Flocculation in 10 wt.% soybean oil-in-water emulsions, stabilized by whey protein isolate (0.75 wt.%), was controlled by adjusting the pH (between 3 and 7) to alter the electrostatic interactions between the droplets. Droplet flocculation was then monitored by measuring the ultrasonic attenuation spectra (1–150 MHz) and by using laser light scattering. Extensive droplet flocculation was observed in the emulsions around the isoelectric point of the proteins (pH 3.5–5.5). Flocculation caused an appreciable change in the ultrasonic attenuation spectra, which was in good qualitative agreement with a theory recently developed to describe the ultrasonic properties of flocculated emulsions. Our results indicate that ultrasonic spectroscopy is a powerful tool for monitoring both the extent and kinetics of flocculation in concentrated emulsions in situ.

Ultrasonic Spectroscopy Study of Globule Aggregation in Parenteral Fat Emulsions Containing Calcium Chloride

Ultrasonic attenuation spectroscopy has been used to study globule aggregation in parenteral fat emulsions. The ultrasonic attenuation spectrum (from 1 to 100 MHz) of a 12 vol % parenteral emulsion was measured at 25 °C. Globule aggregation was then induced in the emulsion by titrating with calcium chloride (0−3.28 mM CaCl2). Dramatic changes in the attenuation spectrum of the emulsion were observed when the globules aggregated, which could be attributed to changes in either the spatial distribution (flocculation) or the size distribution (coalescence) of the globules. The change in globule size during aggregation was calculated using ultrasonic scattering theory assuming that the aggregates are spherical and have properties similar to those of the disperse phase. Ultrasonics has advantages over many other technologies because it can be used to analyze emulsions that are concentrated and optically opaque in situ.

Dispersed/flocculated size characterization of alumina particles in highly concentrated slurries by ultrasonic attenuation spectroscopy

In recent years, several advances have been made in ultrasonic attenuation spectroscopy for monitoring particle size distributions of highly concentrated slurries. This paper presents experimental proof that ultrasonic attenuation spectroscopy is capable of characterizing dispersed or flocculated particle size in highly concentrated slurries. Well-characterized alumina was used for testing the theory. The instrument for measuring ultrasonic attenuation spectra covers a wide frequency range from 1 to 100 MHz and converts them into particle size distributions. It is shown that the particle size distribution obtained before sonication indicates a bimodal distribution, but that after ultrasonication the distribution is reduced to a log–normal for which the median size agrees quite well with a priori known particle size. Hence we confirmed that this technique can differentiate well-dispersed and flocculated particle size in slurries without dilution.

The influence of flocculation on the ultrasonic properties of emulsions: experiment

Droplet flocculation in oil-in-water emulsions has been monitored by ultrasonic attenuation spectroscopy, a technique which is sensitive to changes in the spatial distribution of the droplets within an emulsion. The ultrasonic attenuation spectra (1-150 MHz) of a series of 5 wt% corn oil-in-water emulsions (m) were recorded at 25C. Depletion flocculation was induced in the emulsions by adding various concentrations (7-100 mM) of sodium dodecyl sulphate to the aqueous phase. At low frequencies, the attenuation coefficient of the emulsions decreased with flocculation due to overlap of the thermal waves generated by the droplets. At high frequencies, the attenuation coefficient increased with flocculation due to an increase in scattering by the flocs. The results could be explained using an effective medium theory recently developed to account for the influence of droplet flocculation on the ultrasonic properties of emulsions. The ultrasonic technique was also used to monitor the breakdown of flocs under shear flow. The dependence of the ultrasonic properties of emulsions on flocculation means that ultrasonic attenuation spectroscopy can be used to study interactions among droplets in concentrated emulsions.

Influence of flocculation on the ultrasonic properties of emulsions: theory

A theory is developed to account for the influence of flocculation on the ultrasonic attenuation spectra of emulsions. The theory assumes that flocculated emulsions contain `particles' which have effective properties determined by the size and volume fraction of the individual droplets within the flocs. The theory predicts that the attenuation spectra of emulsions depends on the size of the droplets, the size of the flocs, the packing of the droplets within the flocs and the fraction of droplets which are flocculated.

Ultrasonic Spectroscopy Study of Flocculation and Shear-Induced Floc Disruption in Oil-in-Water Emulsions

Ultrasonic attenuation spectroscopy was used to study flocculation and shear-induced disruption of flocs in oil-in-water emulsions. The ultrasonic attenuation spectra (1 to 150 MHz) of a series of 10 wt% corn oil-in-water emulsions (r32= 0.2 μm) were measured. Depletion flocculation was induced in the emulsions by adding different concentrations (0 to 0.2 wt%) of a nonadsorbing biopolymer (xanthan) to the aqueous phase. At low frequencies, the attenuation coefficient of the emulsions decreased with increasing flocculation due to overlap of the thermal waves generated by the droplets. These observations were in good agreement with a theory recently developed to account for the influence of droplet flocculation on the ultrasonic properties of emulsions. The ultrasonic technique was also used to monitor the breakdown of flocs under shear flow. The dependence of the ultrasonic properties of emulsions on flocculation means that ultrasonic attenuation spectroscopy can be used to study droplet interactions in concentrated emulsions.

Ultrasonic Measurement of Sub‐Micron Particles

AbstractBased on technology described in a Du Pont patent for an offline system, we have developed a prototype in‐line ultrasonic cell for measuring particle size distribution. We have used this cell to verify the Allegra‐Hawley model of ultrasonic attenuation in dilute (&lt; 5 % vol) slurries of sub‐micron ceramic particles, and we are developing a model that can cope with the multiple scattering effects occuring at higher concentrations.In this paper we present the results of attenuation measurements for ultrasound (2–50 MHz) in slurries with concentrations ranging from 0.5 010 to 38 010 (vol). The attenuation is proportional to slurry concentration up to 5 010 (vol) and is predicted by single scattering models. Above approximately 100% concentration, the attenuation is actually lower than expected. For the dilute slurries we find excellent agreement between our measurements and the Allegra‐Hawley calculations, and the effects of the particle size distribution are evident in the ultrasonic attenuation spectrum. These ultrasonic data can be inverted to determine the particle size and concentration in aqueous slurries of sub‐micron particles.

Particle Size Distribution Analysis of Industrial Colloidal Slurries using ultrasonic spectroscopy

AbstractSeveral solid‐liquid suspensions containing submicron particles at moderate to high concentrations (5 to 50 volume percent) are encountered in industrial slurry processing. Measurements of ultrasonic attenuation spectra are used in a newly developed AcoustoPhor particle analysis system to get particle size distributions of such colloidal suspensions. This paper deals with the performance evaluation of the AcoustoPhor system. The automated ultrasonic spectrometer component of the AcoustoPhor system was tested using a reference silicone liquid for its accuracy and precision. The particle size distribution (PSD) estimation capabilities were evaluated using a set of well‐dispersed slurries covering a wide range of particle concentrations. Sensitivity to process variations was evaluated in field tests at a pigment manufacturing plant. The AcoustoPhor system appears to be capable of providing reliable PSD data for inorganic pigment slurries with particle diameters ranging from 0.01 to 100 micrometers at particle concentrations as high as 50 volume percent.

Ultrasonic attenuation spectroscopy research for food dispersion measurement.

Theoretical research work has been done for understanding the principle of the ultrasonic absorption in food dispersion. Four ultrasonic attenuation measurement methods have been developed. These are the through transmission method, through transmission substitution method, pulse echo substitution method, and pulse echo method. The first three methods compare echoes collected from a reference material of known ultrasonic properties with that of the sample. The last method compares reflected echoes collected from measurements on the sample only. An ultrasonic attenuation spectroscopy system for the study of ultrasonic properties of food dispersion has been developed. The results of tests on castor oil are in good agreement with the literature values. Experiments on skimmed milk, semi-skimmed milk, full fat milk, and homogenized milk’s ultrasonic attenuation spectra have been performed. The results demonstrate the effects of both fat content and fat globule particle size on the ultrasonic attenuation characteristics of milk.

Technique for measuring ultrasonic velocity and attenuation spectra in rocks under pressure : Winkler, K W; Plona, T J J Geophys ResV87, NB13, 10 Dec 1982, P10776–10780

An ultrasonic pulse technique has been developed for measuring phase velocity and attenuation spectra in rocks inside a pressure vessel. This technique has been adapted from those used in the non-destructive evaluation field. In essence, a broadband acoustic pulse is directed into a lucite buffer which is followed by the rock sample and another lucite buffer. The pulse partially reflects off both the front and back faces of the sample and the reflected pulses are received by the transmitting transducer. Digital recording and signal processing techniques are used to analyze the signal. After Fourier transforming each pulse, correcting for diffraction effects and allowing for partial reflections at the interfaces, the phase shift between pulses at each frequency yields the phase velocity and the amplitude reduction gives the attenuation. Tests on synthetic materials show that as currently implemented, the technique produces reliable measurements at frequencies above 400 kHz. Velocity and attenuation spectra are shown for brine saturated Massilon and Boise sandstones at different effective pressures.

Technique for measuring ultrasonic velocity and attenuation spectra in rocks under pressure

An ultrasonic pulse technique has been developed for measuring phase velocity and attenuation spectra in rocks inside a pressure vessel. This technique has been adapted from those used in the nondestructive evaluation field. In essence, a broadband acoustic pulse is directed into a lucite buffer, which is followed by the rock sample and another lucite buffer. The pulse partially reflects off both the front and back faces of the sample, and the reflected pulses are received by the transmitting transducer. Digital recording and signal processing techniques are used to analyze the signal. After Fourier transforming each pulse, correcting for diffraction effects, and allowing for partial reflections at the interfaces, the phase shift between pulses at each frequency yields the phase velocity and the amplitude reduction gives the attenuation. Tests on synthetic materials show that as currently implemented, the technique produces reliable measurements at frequencies above 400 kHz. Velocity and attenuation spectra are shown for brine saturated Massilon and Boise sandstones at different effective pressures.

Relaxation spectra of copper(II)-ATP complexes at low pH

1. 1. Acidic solutions (pH 1–5) of copper(II)-adenosine triphosphate yield ultrasonic attenuation spectra consisting of three maxima. From the concentration and pH dependence of these peaks, and by comparison with the spectra of low pH ATP, CuCl 2 and Cu 3(PO 4) 2 solutions, we have assigned the spectrum as follows. The overall reaction which fits the ultrasonic attenuation data best is Cu 2+ + H 2 ATP 2− ag CuHATP − + H + The shortest relaxation time (approx. 2 · 10 −9 s) is ascribed to penetration of the inner copper(II) hydration shell by the ligand. The next slower process (approx. 1 · 10 −8 s) is then due to chelate ring closure of the species formed in the faster step. The lowest frequency peak (< 2 MHz) has been taken to be either a characteristic of aqueous copper(II) ion, as already observed in other systems ( e.g. CuSO 4), or to be due to formation of another (minority) complex species such as CuH 2ATP. In either case, the presence of this peak does not interfere with the kinetic analysis of the faster processes. 2. 2. On the assumption that formation of copper(II) complexes follows the established pattern of other divalent transition metal ions, we obtain at 25 ·C and variable ionic strength (0.1–0.8 M), 8.8 · 10 8 s −1 for the water elimination rate constant, and 6.3 · 10 7 s −1 for the sterically controlled ring closure. The ion-pair formation constant consistent with the data is 16 M −1. The absolute value of the standard volume change, | Δ V c| has been estimated to be 42 ml · mole −1 for the above overall reaction. 3. Although the experimental error associated with the determination of the relaxation maxima is on the order of 10–20%, the values of the rate constants, ion-pair formation constant and standard volume changes are reliable to only a factor of approximately two, due to uncertainties in solution composition and approximations made in solving the rate equations.