Review of High-Frequency Ultrasounds Emulsification Methods and Oil/Water Interfacial Organization in Absence of any Kind of Stabilizer

Abstract

Emulsions are multiphasic systems composed of at least two immiscible phases. Emulsion formulation can be made by numerous processes such as low-frequency ultrasounds, high-pressure homogenization, microfluidization, as well as membrane emulsification. These processes often need emulsifiers’ presence to help formulate emulsions and to stabilize them over time. However, certain emulsifiers, especially chemical stabilizers, are less and less desired in products because of their negative environment and health impacts. Thus, to avoid them, promising processes using high-frequency ultrasounds were developed to formulate and stabilize emulsifier-free emulsions. High-frequency ultrasounds are ultrasounds having frequency greater than 100 kHz. Until now, emulsifier-free emulsions’ stability is not fully understood. Some authors suppose that stability is obtained through hydroxide ions’ organization at the hydrophobic/water interfaces, which have been mainly demonstrated by macroscopic studies. Whereas other authors, using microscopic studies, or simulation studies, suppose that the hydrophobic/water interfaces would be rather stabilized thanks to hydronium ions. These theories are discussed in this review.

Stability of Aqueous Suspensions of COOH-Decorated Carbon Nanotubes to Organic Solvents, Esterification, and Decarboxylation

“…Also, in the case of hydrophobic surfaces, an alternative charging mechanism connected with the HO − adsorption should be taken into account. 28 Summarizing, the colloidal stability of an aqueous suspension of COOH-decorated SWCNT with respect to inorganic electrolytes drops sharply on substantial addition of methanol, ethanol, acetonitrile, and acetone. Contrary to it, in the case of cationophilic (protophilic) solvents, such as DMF and DMSO, the critical concentrations of coagulation are much closer to those in water.…”

“…For instance, the CCC ratio in water and in 80 vol % ethanol changes from 83 for the initial sample to 15.5 (methylated for 240 h); 24 (heated at 350 °C); and 1.9 (heated at 600 °C). Also, in the case of hydrophobic surfaces, an alternative charging mechanism connected with the HO – adsorption should be taken into account …”

Microemulsification from single laser-induced cavitation bubbles

“…2002; Hijo, Guinosa & Silva 2022; Perrin et al. 2022). Insights into the mechanism on how a particular technique leads to droplet deformation and fragmentation are pertinent for improving the current emulsification techniques (Zhou et al.…”

“…For example, during the collapse, mild asymmetries in the flow field are amplified. The resulting liquid jets drive shear flow (Canselier et al 2002;Hijo, Guinosa & Silva 2022;Perrin et al 2022). Insights into the mechanism on how a particular technique leads to droplet deformation and fragmentation are pertinent for improving the current emulsification techniques (Zhou et al 2022).…”

Experimental and numerical analysis of the emulsification of oil droplets in water with high frequency focused ultrasound

“…These techniques allow for the production of small droplets via simple design and relatively less energy requirements. However, they encounter limitations due to significant usage of synthetic surfactants, difficult process scale-up, membrane fouling and low output [13] , [14] . Low energy emulsification may require surfactant-to-oil ratio (SOR) of more than 0.5 in order to provide good dispersion.…”