A computational and experimental study on acoustic pressure for ultrasonically formed oil-in-water emulsion

Prandtl and Ohnesorge numbers dependent of ultrasonic horn energy in Newtonian liquid under batch and continuous flow

The level of knowledge on the non-thermal contribution of ultrasonic wave's energy to perform physico-chemical phenomena is one of the bottlenecks for the commercialization purposes. Under constant nominal power of transducer (Pn), the input electrical power (Pin) is less and sensitive to the medium's physical properties. This study attempts to assess the conversion of acoustic to thermal power experimentally and numerically using COMSOL Multiphysis@ for a 24 kHz horn-type sonicator through a medium without any sono-chemical effect. Single- and homogeneous two-phase Newtonian mixtures of sunflower oil and water (o/w) with a relatively wide range of density (914-998 kg/m3) and viscosity (0.5-63.5 mPa.s) were irradiated in a lab-scale vessel (1 L) under batch and continuous flow configuration. The direct influence of Pn (80-400 W) and o/w ratio (0-1) on temperature rise and subsequent thermo-physical properties of liquid and the indirect influence on Pin and thermal energy conversion (TEC) were investigated employing calorimetric method. A new engineering concept including a power factor correlation was proposed and validated for prediction of Pin as a function of liquid space velocity (ϑ), temperature, Prandtl (Pr) and Ohnesorge (Oh) dimensionless groups. The results showed that under constant temperature and Pn, increasing Pr and Oh increased Pin with a similar trend for both modes of operation. An increase in temperature directly led to a decrease in Pin with a power factor closed to "-1". The Pin in continuous flow was higher compared to batch configuration at similar temperature, liquid properties, and Pn. This effect was more significant with increasing ϑ. An increase in ϑ at constant Pn led to a decrease in the inlet/outlet temperature difference in continuous flow and an increase in Pin. Increasing Pn resulted in higher TEC for both configurations; however, TEC was relatively lower in continuous flow than batch configuration indicating more efficient sonication in continuous flow.

Tailoring Microemulsification Techniques for the Encapsulation of Diverse Cargo: A Systematic Analysis of Poly (Urea-Formaldehyde) Microcapsules

Cargo encapsulation through emulsion-based methods has been pondered over the years. Although several microemulsification techniques have been employed for the microcapsule's synthesis, there are still no clear guidelines regarding the suitability of one technique over the others or the impacts on the morphological and physicochemical stability of the final particles. Therefore, in this systematic study, we investigated the influence of synthesis parameters on the fabrication of emulsion-based microcapsules concerning morphological and physicochemical properties. Using poly(urea-formaldehyde) (PUF) microcapsules as a model system, and after determining the optimal core/shell ratio, we tested three different microemulsification techniques (magnetic stirring, ultrasonication, and mechanical stirring) and two different cargo types (100% TEGDMA (Triethylene glycol dimethacrylate) and 80% TEGDMA + 20% DMAM (N,N-Dimethylacrylamide)). The resulting microcapsules were characterized via optical and scanning electron microscopies, followed by size distribution analysis. The encapsulation efficiency was obtained through the extraction method, and the percentage reaction yield was calculated. Physicochemical properties were assessed by incubating the microcapsules under different osmotic pressures for 1 day and 1, 2, or 4 weeks. The data were analyzed statistically with one-way ANOVA and Tukey's tests (α = 0.05). Overall, the mechanical stirring resulted in the most homogeneous and stable microcapsules, with an increased reaction yield from 100% to 50% in comparison with ultrasonication and magnetic methods, respectively. The average microcapsule diameter ranged from 5 to 450 µm, with the smallest ones in the ultrasonication and the largest ones in the magnetic stirring groups. The water affinities of the encapsulated cargo influenced the microcapsule formation and stability, with the incorporation of DMAM leading to more homogeneous and stable microcapsules. Environmental osmotic pressure led to cargo loss or the selective swelling of the shells. In summary, this systematic investigation provides insights and highlights commonly overlooked factors that can influence microcapsule fabrication and guide the choice based on a diligent analysis of therapeutic niche requirements.

Dynamics of oil-water interface at the beginning of the ultrasonic emulsification process

A lot of effort has been dedicated in recent years towards understanding the basics of cavitation induced emulsification, mainly in the form of single cavitation bubbles. Regarding bulk acoustic emulsification, a lot less research has been done. In our here presented work we utilize advanced high-speed observation techniques in visible light and X-Rays to build upon that knowledge and advance the understanding of bulk emulsion preparation. During research we discovered that emulsion formation has an acute impact on the behavior of the interface and more importantly on its position relative to the horn, hence their interdependence must be carefully studied. We did this by observing bulk emulsification with 2 cameras simultaneously and corroborating these measurements with observation under X-Rays. Since the ultrasonic horns location also influences interface behavior, we shifted its initial position to different locations nearer to and further away from the oil-water interface in both phases. We found that a few millimeters distance between the horn and interface is not enough for fine emulsion formation, but that they must be completely adjacent to each other, with the horn being located inside the oil-water interface. We also observed some previously undiscovered phenomena, such as the splitting of the interface to preserve continuous emulsion formation, climbing of the interface up the horn and circular interface protrusions towards the horn forming vertical emulsion streams. Interestingly, no visible W/O emulsion was ever formed during our experiments, only O/W regardless of initial horn position.

Effect of slit dual-frequency ultrasonic emulsification technology on the stability of walnut emulsions

A highly hygienic walnut emulsion beverage was prepared by using a slit dual-frequency emulsification technique. The optimal ultrasonic parameters were studied as a model system: the ultrasonic time of 50 min, the ultrasonic power density of 260 W/L, and a dual-frequency ultrasonic combination of 28/68 kHz. Walnut emulsion with an average mean volume diameter of 2.05 µm, a Zeta potential absolute value of 40 mV was obtained after ultrasonic treatment, and the emulsion stability could be maintained for more than 14 days without phase separation. At the lowest ultrasonic energy input, the vibrating emulsion could promote droplet aggregation. However, excessive energy input could result in sample overtreatment and reduced emulsion activity. The laser scanning confocal microscope (LSCM) and transmission electron microscope (TEM) confirmed that walnut emulsion processed by slit dual-frequency ultrasonic had pretty high stability. Therefore, the slit dual-frequency ultrasonic emulsification technique was found to be well suited for the preparation of complex and fine oil-in-water food emulsions.

One-pot ultrasonic cavitational emulsification of phytosterols oleogel-based flavor emulsions and oil powder stabilized by natural saponin

Phytosterols oleogel-based flavor emulsions were successfully fabricated for the first time using natural tea saponin as emulsifier and one-pot ultrasonic technique. The effects of ultrasonic time and power, surfactant concentration, and type of flavor oils (e.g., orange, lemon and peppermint) on the emulsion droplet size were investigated. Submicron emulsions with a dispersed phase made by flavor oil (20 wt%) + phytosterol (4 wt%) were stabilized with 3 wt% saponin were obtained by applying an ultrasonic time of 5 min and ultrasonic power of 280 W. The natural tea saponin emulsions exhibited a superior stability and encapsulation efficiency of phytosterol, compared to traditional emulsifiers. Flavor oil-phytosterol enriched powders were prepared by spray-drying and characterized by SEM, XRD and repose angle. The natural saponin encapsulated oil + phytosterol powders had excellent fluidity, redispersion behavior and low phytosterol crystallinity. It was demonstrated that ultrasound is an effective and suitable technique for fabricating fortified flavor emulsions and microcapsules, which may be used for developing functional lipids-based applications in the food, beverage and cosmetic industries.

An Analysis of Acoustic Cavitation Thresholds of Water Based on the Incubation Time Criterion Approach

Researchers are still working on the development of models that facilitate the accurate estimation of acoustic cavitation threshold. In this paper, we have analyzed the possibility of using the incubation time criterion to calculate the threshold of the onset of acoustic cavitation depending on the ultrasound frequency, hydrostatic pressure, and temperature of a liquid. This criterion has been successfully used by earlier studies to calculate the dynamic strength of solids and has recently been proposed in an adapted version for calculating the cavitation threshold. The analysis is carried out for various experimental data for water presented in the literature. Although the criterion assumes the use of macroparameters of a liquid, we also considered the possibility of taking into account the size of cavitation nuclei and its influence on the calculation result. We compared the results of cavitation threshold calculations done using the incubation time criterion of cavitation and the classical nucleation theory. Our results showed that the incubation time criterion more qualitatively models the results of experiments using only three parameters of the liquid. We then discussed a possible relationship between the parameters of the two approaches. The results of our study showed that the criterion under consideration has a good potential and can be conveniently used for applications where there are special requirements for ultrasound parameters, maximum negative pressure, and liquid temperature.

Applying ultrasonic fields to separate water contained in medium-gravity crude oil emulsions and determining crude oil adhesion coefficients

Separating produced water is a key part of production processing for most crude oils. It is required for quality reasons, and to avoid unnecessary transportation costs and prevent pipework corrosion rates caused by soluble salts present in the water. A complicating factor is that water is often present in crude oil in the form of emulsions. Experiments were performed to evaluate the performance of ultrasonic fields in demulsifying crude oil emulsions using novel pipe-form equipment. A horn-type piezoelectric ultrasonic transducer with a frequency of 20 kHz and power ranging from 80 W to 1000 W was used for experimental purposes. The influences of the intensity of ultrasonic fields, ultrasonic irradiation time, and the initial water content of crude oils were evaluated to establish the rate of water segregation from oil. The experiments applied ultrasonic-field intensities of 0.25 W/cm³, 0.5 W/cm³, 0.75 W/cm³ and 1 W/cm³ to synthetic emulsions with 10%, 15%, 20%, and 25% of the water in crude oil. Crude oil demulsification occurred for each ultrasonic field intensity tested for all the samples tested. Function β involving adhesion coefficients was expressed in terms of wave-field intensity and initial concentration of water in each of the three crude oil samples tested. The experiments demonstrated that despite the absence of any chemical demulsifier involved, water separation caused by applying ultrasonic fields was effective and occurred rapidly. As the intensity of the ultrasonic field applied increased, the amount of water segregated from crude oil also increased. Subjected to constant field intensity, higher initial water cuts (up to 15% or so) in the crude oil samples and higher ultrasonic irradiation times, resulted in greater segregation of water from crude oil in percentage terms. However, in samples with initial water cuts of 20+% long irradiation times (~5 min), resulted in a decline in water separation compared to 2-min tests. Ultrasonic field treatments offer commercially-viable and environmentally-friendly alternatives to treatments using chemical demulsifiers as they reduce desalination requirements of wastewater.

Recent advances in applications of power ultrasound for petroleum industry

Power ultrasound, as an emerging green technology has received increasing attention of the petroleum industry. The physical and chemical effects of the periodic oscillation and implosion of acoustic cavitation bubbles can be employed to perform a variety of functions. Herein, the mechanisms and effects of acoustic cavitation are presented. In addition, the applications of power ultrasound in the petroleum industry are discussed in detail, including enhanced oil recovery, oil sand extraction, demulsification, viscosity reduction, oily wastewater treatment and oily sludge treatment. From the perspective of industrial background, key issue and resolution mechanism, current applications and future development of power ultrasound are discussed. In addition, the effects of acoustic parameters on treatment efficiency, such as frequency, acoustic intensity and treatment time are analyzed. Finally, the challenges and outlook for industrial application of power ultrasound are discussed.

Green synthesis of garlic oil nanoemulsion using ultrasonication technique and its mechanism of antifungal action against Penicillium italicum

Penicillium italicum (P. italicum) can cause significant economic loss of fruits and vegetables. Although garlic oil (GO) is an effective antimicrobial agent, the unstability and hydrophobicity limit its use as an environmentally friendly alternative to the conventional antibiotics against P. italicum. In this study, we focused on the fabrication and characterization of a functional GO nanoemulsion (NE) using ultrasonic technique and revealed the antifungal mechanism of the GO NE on P. italicum based on morphological, structural and molecular analyses. The optimal hydrophilic lipophilic balance (HLB) value determined for GO was 14 through the combination of Tween 80 and Span 80. Then the Box-Benhnken Design (BBD) was applied to produce the GO NE and the effects of different fabrication parameters on the particle size were evaluated. The optimal GO NE was selected with the GO concentration of 5.5%, the Smix concentration of 10%, the ultrasonic time of 5 min and the power of 50%. This GO NE had the smallest particle size of 52.27 nm, the best antifungal effect and the most stability. Furthermore, the antifungal mechanism of the GO NE on P. italicum was evaluated by extracellular conductivity, micro-Raman spectra, fluorescence imaging and scanning electron microscopy (SEM) imaging. The results presented that the GO NE retained the antifungal active ingredients. The fungal cell structure and morphology were malformed after treated with the GO NE and the lipids, nucleic acids and protein of P. italicum were destructed. Finally, the optimal GO NE was applied in vivo and P. italicum in citrus was successfully inhibited. It indicated that the optimal GO NE had the better antifungal activity against P. italicum than the pure GO. Besides, the minimum inhibitory concentration (MIC) of GO after preparing into the NE was changed from 3.7% to 0.01265% with about 300 times improvement of bioavailability. Therefore, the synthetic GO NE which promoted the bioavailability of GO was recommended as a promising alternative to inhibit P. italicum in vegetables and fruits.