The phenomenon of surfactant micelle ordering (i.e., stratification) in emulsion films was investigated using the reflected-light microinterferometric technique. In thinning films formed from a nonionic micellar solution of ethoxylated alcohol (1 wt %), it was found that the small droplets (i.e., less than 5 µm) are separated by thick (>0.1 µm) stable films containing surfactant micelles in multilayers that prevent droplet flocculation and coalescence. The Ostwald ripening process governs emulsion stability over a long-term. The direct microscopic observations of the evolution of the drop size distribution over time of hexadecane drops (∼25 vol %) dispersed in an aqueous micellar solution (≈ 120 times critical micellar concentration) was compared with that calculated from the Ostwald ripening model.
Microstructural engineering is becoming notably important
in the
realization of cobalt-free, high-nickel layered oxide cathodes for
lithium-ion batteries since it is one of the most effective ways to
improve the overall performance by enhancing the mechanical and electrochemical
properties of cathodes. In this regard, various dopants have been
investigated to improve the structural and interfacial stabilities
of cathodes with doping. Yet, there is a lack of a systematic understanding
of the effects of dopants on microstructural engineering and cell
performances. Herein, we show controlling the primary particle size
by adopting dopants with different oxidation states and solubilities
in the host structure as an effective way for tuning the cathode microstructure
and performance. The reduction in the primary particle size of cobalt-free
high-nickel layered oxide cathode materials, e.g., LiNi0.95Mn0.05O2 (NM955), with high-valent dopants,
such as Mo6+ and W6+, gives a more homogeneous
distribution of Li during cycling with suppressed microcracking, cell
resistance, and transition-metal dissolution compared to lower-valent
dopants, such as Sn4+ and Zr4+. Accordingly,
this approach offers promising electrochemical performance with cobalt-free
high-nickel layered oxide cathodes.
This article presents the results of our recent research on the texture and stability of oil-in-water emulsions containing sucrose ester and proteins. We used both the direct microscopic imaging and nondestructive back-light scattering (Kossel diffraction) techniques to evaluate the emulsion texture and the energy barrier between droplets for two different emulsifier compositions with and without the proteins present. The microinterferometric method employing our capillary force balance was used to study the stability of the confined thin film (containing surfactant micelles and proteins) between two droplets. In addition to the film stability, we also measured the second virial coefficient of the micellar solutions with and without protein and assessed the intermicellar interaction and related it to the stabilities of the emulsions prepared using two different emulsifier compositions. The effect of protein on the oil-in-water emulsion stability was also assessed and was found to lead to the depletion attraction between droplets, resulting in a less stable emulsion. The results offer new insight into the understanding of how the micellar interactions in the presence of proteins affect emulsion texture and stability.
We used a non-destructive Kossel diffraction technique based on the principle of backlight scattering to characterize the microstructure of an oil-in-water emulsion and ring formation in a model food-beverage system. Through this technique, we quantified the emulsion texture inside the ring by radial distribution function. We also studied the stability of soybean oil-in-water emulsions by determining the structure factor and effective droplet interaction potential and by measuring the droplet size distribution. We monitored the increase in the oil volume fraction inside the ring and compared it with the theoretically predicted values using the Stokes equation for creaming, taking into account the polydispersity in droplet size. Good agreement was found between the experimental results and theoretical predictions. We investigated the phenomenon of oil spreading at the air-emulsion interface using the differential interferometric technique.
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