Emulsions ultrasonic characterization

Hibberd, D.J., Holmes, A.K., Garrood, M., Fillery-Travis, A.J., Robins, M.M., Challis, R.E. 1997a. Ultrasonic characterization of flocculation in oil-in-water emulsions. In Food Colloids—Proteins, Lipids and Polysaccharides (E. Dickinson, B. Bergenstahl, eds.), pp. 137-149, Royal Society of Chemistry, Cambridge. 

Although NMRI is a very well-suited experimental technique for quantifying emulsion properties such as velocity profiles, droplet concentration distributions and microstructural information, several alternative techniques can provide similar or complementary information to that obtained by NMRI. Two such techniques, ultrasonic spectroscopy and diffusing wave spectroscopy, can be employed in the characterization of concentrated emulsions in situ and without dilution [45],... 

In terms of measuring emulsion microstructure, ultrasonics is complementary to NMRI in that it is sensitive to droplet flocculation [54], which is the aggregation of droplets into clusters, or floes, without the occurrence of droplet fusion, or coalescence, as described earlier. Flocculation is an emulsion destabilization mechanism because it disrupts the uniform dispersion of discrete droplets. Furthermore, flocculation promotes creaming in the emulsion, as large clusters of droplets separate rapidly from the continuous phase, and also promotes coalescence, because droplets inside the clusters are in close contact for long periods of time. Ideally, a full characterization of an emulsion would include NMRI measurements of droplet size distributions, which only depend on the interior dimensions of the droplets and therefore are independent of flocculation, and also ultrasonic spectroscopy, which can characterize flocculation properties. 

D.J. McClements, "The use of ultrasonics for characterizing fats and emulsions", Ph.D. Thesis, Department of Food Science, University of Leeds (1988). 

It is not possible to discuss all the methods available for characterizing foods critically and systematically in a single volume. Methods pertaining to interfaces (food emulsions, foams, and dispersions), fluorescence, ultrasonics, nuclear magnetic resonance, electron spin resonance, Fourier-transform infrared and near infrared spectroscopy, small-angle neutron scattering, dielectrics, microscopy, rheology, sensors, antibodies, flavor and aroma analysis are included. 

DJ McClements. The Use of Ultrasonics for Characterizing Fats and Emulsions. PhD dissertation. Leeds Leeds University, 1988. 

A suspected water gel is examined on a microscope slide to identify the microspheres used in slurry and emulsion explosives. The gel is directly extracted with methanol, which dissolves the amine salt, and a small amount of NH4NO3. TLC on a cellulose plate using a chloroform-methanol-water system separates the sensitizers. The plate is sprayed with ni-nhydrin and heated to visualize the amine salt. A second spray with diphenylamine in ethanol followed by long-wave UV irradiation visualizes the NFi4N03 if desired. Alternatively, the methanol extract may be evaporated to near dryness, redissolved in water, and analyzed by IC to identify the sensitizer. An intact sample can also be extracted with water using either a small homogenizer or ultrasonic agitation to disrupt the gel structure. Microspheres float on the surface and are removed for examination by SEM-EDX to characterize the manufacturer. Spot tests and IC identify ammonium, calcium, and nitrate ions in the water extract. Flake aluminum, if present, is identified as described above. 

A. Shanmugam, M. Ashokkumar, Ultrasonic preparation of stable flax seed oil emulsions in dairy systems—physicochemical characterization. Food Hydrocolloids 39, 151-162 (2014)... 

A. Shanmugam, M. Ashokkumar, Characterization of ultrasonically prepared flaxseed oil enriched beverage/carrot juice emulsions and process-induced changes to the functional properties of carrot juice. Food Bioprocess Technol. 8, 1258-1266 (2015)... 

HOPE, PS, and HDPE/PS (80/20) blends to characterize their structural development during extrusion in the presence of ultrasonic oscillations. The extruder set-up, equipped with a capillary die and an ultrasonic device, is shown in Figure 8.27. The slopes of log G versus log G" for HDPE/PS (80/20) blends in the low-frequency region (i.e., long relaxation time) and an emulsion model were used to characterize the ultrasonic enhancement of the compatibility of the blends. The results showed that ultrasonic oscillations could reduce the interfacial tension and enhance the compatibility of the blends, and this was consistent with the data provided by Chen et al. [99]. 

Many ofthe technologies listed above can be used only with dilute suspensions. However, there are instances where particle characterization has to be performed in a concentrated phase in which dynamic processes such as aggregation, agglomeration, or flocculation may occur at a much faster rate. In other instances, such as in emulsion systems, dilution just is not feasible because the system may change due to the dilution process. The analysis of such concentrated samples is especially important in on-line processes where particles naturally exist in concentrated states. Since sound waves can travel through concentrated suspensions, ultrasonic analysis provides a mean to characterize particulate systems at concentrations up to 60% hy volume [34]. 

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