Sustained release formulations of citronella oil nanoemulsion using cavitational techniques

Nanoemulsion synthesis has proven to be an effective way for transportation of immobile, insoluble bioactive compounds. Citronella Oil (lemongrass oil), a natural plant extract, can be used as a mosquito repellent and has less harmful effects compared to its available market counterpart DEET (N, N-Diethyl-meta-toluamide). Nanoemulsion of citronella oil in water was prepared using cavitation-assisted techniques while investigating the effect of system parameters like HLB (Hydrophilic Lipophilic Balance), surfactant concentration, input energy density and mode of power input on emulsion quality. The present work also examines the effect of emulsification on release rate to understand the relationship between droplet size and the release rate. Minimum droplet size (60 nm) of the emulsion was obtained at HLB of 14, S/O¹ ratio of 1.0, ultrasound amplitude of 50% and irradiation time of 5 min. This study revealed that hydrodynamic cavitation-assisted emulsification is more energy efficient compared to ultrasonic emulsification. It was also found that the release rate of nanoemulsion enhanced as the droplet size of emulsion reduced.     

Ultrasonic emulsification of eucalyptus oil nanoemulsion: Antibacterial activity against Staphylococcus aureus and wound healing activity in Wistar rats

The plant derived essential oil nanoemulsion was prepared using a mixture of components containing eucalyptus oil as organic phase, water as continuous phase, and non ionic surfactant, Tween 80, as emulsifier at a particular proportion of 1:1 v/v%. The ultrasonication was applied for varied processing time from 0 to 30 min to study the effect of time on the formation of nanoemulsion and physical stability of formulation by this method. The transparency and stability of emulsion was enhanced when the sonication time was increased compared to hand blender emulsion. The most stable nanoemulsion was obtained in 30 min sonication having the mean droplet diameter of 3.8 nm. The antibacterial studies of nanoemulsion against Staphylococcus aureus by time kill analysis showed complete loss of viability within 15 min of interaction. Observations from scanning electron microscopy of treated bacterial cells confirmed the membrane damage compared to control bacteria. Furthermore, the wound healing potential and skin irritation activity of the formulated nanoemulsion in Wistar rats, suggested non-irritant and higher wound contraction rate with respect to control and neomycin treated rats. These results proposed that the formulated system could be favourable for topical application in pharmaceutical industries.     

Impact of process parameters in the generation of novel aspirin nanoemulsions – Comparative studies between ultrasound cavitation and microfluidizer

In the present investigation, the operating efficiency of a bench-top air-driven microfluidizer has been compared to that of a bench-top high power ultrasound horn in the production of pharmaceutical grade nanoemulsions using aspirin as a model drug. The influence of important process variables as well as the pre-homogenization and drug loading on the resultant mean droplet diameter and size distribution of emulsion droplets was studied in an oil-in-water nanoemulsion incorporated with a model drug aspirin. Results obtained show that both the emulsification methods were capable of producing very fine nanoemulsions containing aspirin with the minimum droplet size ranging from 150 to 170 nm. In case of using the microfluidizer, it has been observed that the size of the emulsion droplets obtained was almost independent of the applied microfluidization pressure (200–600 bar) and the number of passes (up to 10 passes) while the pre-homogenization and drug loading had a marginal effect in increasing the droplet size. Whereas, in the case of ultrasound emulsification, the droplet size was generally decreased with an increase in sonication amplitude (50–70%) and period of sonication but the resultant emulsion was found to be dependent on the pre-homogenization and drug loading. The STEM microscopic observations illustrated that the optimized formulations obtained using ultrasound cavitation technique are comparable to microfluidized emulsions. These comparative results demonstrated that ultrasound cavitation is a relatively energy-efficient yet promising method of pharmaceutical nanoemulsions as compared to microfluidizer although the means used to generate the nanoemulsions are different.     

Process optimization of ultrasound-assisted curcumin nanoemulsions stabilized by OSA-modified starch

This study reports on the process optimization of ultrasound-assisted, food-grade oil–water nanoemulsions stabilized by modified starches. In this work, effects of major emulsification process variables including applied power in terms of power density and sonication time, and formulation parameters, that is, surfactant type and concentration, bioactive concentration and dispersed-phase volume fraction were investigated on the mean droplet diameter, polydispersity index and charge on the emulsion droplets. Emulsifying properties of octenyl succinic anhydride modified starches, that is, Purity Gum 2000, Hi-Cap 100 and Purity Gum Ultra, and the size stability of corresponding emulsion droplets during the 1 month storage period were also investigated. Results revealed that the smallest and more stable nanoemulsion droplets were obtained when coarse emulsions treated at 40% of applied power (power density: 1.36 W/mL) for 7 min, stabilized by 1.5% (w/v) Purity Gum Ultra. Optimum volume fraction of oil (medium chain triglycerides) and the concentration of bioactive compound (curcumin) dispersed were 0.05 and 6 mg/mL oil, respectively. These results indicated that the ultrasound-assisted emulsification could be successfully used for the preparation of starch-stabilized nanoemulsions at lower temperatures (40–45 °C) and reduced energy consumption.     

Physiochemical and cytotoxicity study of TPGS stabilized nanoemulsion designed by ultrasonication method

The main aim of the present work was to prepare TPGS stabilized D-α-Tocopherol, lemon oil, tween-80, and water nanoemulsion by low cost and highly effective sonication method. The prepared nanoemulsion showed good stability for 60 days at variable temperature conditions i.e. 4, 25 and 37 °C. The tolerance of the prepared nanoemulsion to salt (50 mM–500 mM) and pH (pH 2–pH 7.4) was also studied. The morphology and droplet size of pure and quinine loaded nanoemulsion was characterized with transmission electron microscopy. The prepared formulation was transparent and the obtained average particle size ranged between 25 nm and 35 nm. The nanoemulsion was found to be non toxic. The cell viability study of pure nanoemulsion carried out on Hep G2 cells revealed that the cell viability was 100%. The formulation further exhibited high quinine loading and release capacity with cumulative release up to 76 ± 2% and 65 ± 2% at pH 7.4 and pH 5.5 respectively. The interaction between quinine and vitamins (riboflavin, thiamine and biotin) was also carried out (aqueous medium). The study revealed that riboflavin had strong interaction with quinine and vitamins vis-à-vis thiamine and biotin.     

Ultrasonic emulsification of parenteral valproic acid-loaded nanoemulsion with response surface methodology and evaluation of its stability

Response surface methodology (RSM) was used to optimize the formulation of a nanoemulsion for central delivery following parenteral administration. A mixture of medium-chain triglyceride (MCT) and safflower seed oil (SSO) was determined as a sole phase from the emulsification properties. Similarly, a natural surfactant (lecithin) and non-ionic surfactant (Tween 80) (ratio 1:2) were used in the formulation. A central composite design (CCD) with three-factor at five-levels was used to optimize the processing method of high energy ultrasonicator. Effects of pre-sonication ultrasonic intensity (A), sonication time (B), and temperature (C) were studied on the preparation of nanoemulsion loaded with valproic acid. Influence of the aforementioned specifically the effects of the ultrasonic processing parameters on droplet size and polydispersity index were investigated. From the analysis, it was found that the interaction between ultrasonic intensity and sonication time was the most influential factor on the droplet size of nanoemulsion formulated. Ultrasonic intensity (A) significantly affects the polydispersity index value. With this optimization method, a favorable droplet size of a nanoemulsion with reasonable polydispersity index was able to be formulated within a short sonication time. A valproic acid loaded nanoemulsion can be obtained with 60% power intensity for 15 min at 60 °C. Droplet size of 43.21 ± 0.11 nm with polydispersity index of 0.211 were produced. The drug content was then increased to 1.5%. Stability study of nanoemulsion containing 1.5% of valproic acid had a good stability as there are no significant changes in physicochemical aspects such as droplet size and polydispersity index. With the characteristisation study of pH, viscosity, transmission electron microscope (TEM) and stability assessment study the formulated nanoemulsion has the potential to penetrate blood–brain barrier in the treatment of epilepsy.     

Fish oil based vitamin D nanoencapsulation by ultrasonication and bioaccessibility analysis in simulated gastro-intestinal tract

Recently, nanoemulsions have been employed for different applications including food and drug industries for efficient nutrient delivery system. In this study, vitamin D (a lipophilic molecule) was encapsulated in fish oil for higher oral bioavailability. The oil-in-water nanoemulsion was formulated by ultrasonication technique with a droplet size range of 300–450 nm and a shelf life of more than 90 days. The influence of oil, water and surfactant concentration was investigated by phase diagram. The formulated nanoemulsion had encapsulation efficiency in the range of 95.7–98.2%. Further, nanoemulsion passed through simulated gastro-intestinal tract revealed an increased bioavailability than non-encapsulated vitamin. Thus, the formulation can be used as a drug delivery vehicle for various lipophilic compounds. Till date, no one have fabricated an efficient nano-vehicle for the delivery of vitamin D as well as analyzed the efficient delivery system in simulated GI-tract, this is first of its kind study in this regard. This can be scaled up further after analyzing the safety aspects.     

Enhanced photoacoustic imaging in tissue-mimicking phantoms using polydopamine-shelled perfluorocarbon emulsion droplets

The current work features process parameters for the ultrasound (25 kHz)-assisted fabrication of polydopamine-shelled perfluorocarbon (PDA/PFC) emulsion droplets with bimodal (modes at 100–600 nm and 1–6 µm) and unimodal (200–600 nm) size distributions. Initial screening of these materials revealed that only PDA/PFC emulsion droplets with bimodal distributions showed photoacoustic signal enhancement due to large size of their optically absorbing PDA shells. Performance of this particular type of emulsion droplets as photoacoustic agents were evaluated in Intralipid®–India ink media, mimicking the optical scattering and absorbance of various tissue types. From these measurements, it was observed that PDA/PFC droplets with bimodal size distributions can enhance the photoacoustic signal of blood-mimicking phantom by up to five folds in various tissue-mimicking phantoms with absorption coefficients from 0.1 to 1.0 cm⁻¹. Furthermore, using the information from enhanced photoacoustic images at 750 nm, the ultimate imaging depth was explored for polydopamine-shelled, perfluorohexane (PDA/PFH) emulsion droplets by photon trajectory simulations in 3D using a Monte Carlo approach. Based on these simulations, maximal tissue imaging depths for PDA/PFH emulsion droplets range from 10 to 40 mm, depending on the tissue type. These results demonstrate for the first time that ultrasonically fabricated PDA/PFC emulsion droplets have great potential as photoacoustic imaging agents that can be complemented with other reported characteristics of PDA/PFC emulsion droplets for extended applications in theranostics and other imaging modalities.     

Formulation and physiochemical study of α-tocopherol based oil in water nanoemulsion stabilized with non toxic,biodegradable surfactant: Sodium stearoyl lactate

The unique properties such as high optical clarity, stability and enhanced bioavailability of nanoemulsion make them useful for food, cosmetic and pharmaceutical industries. In this work, sodium stearoyl lactate and Tween 80 surfactants were collectively used to fabricate alpha tocopherol based oil in water nanoemulsion using high energy ultrasonication method. The spherical nature of pure and drug loaded nanoemulsion has been confirmed with transmission electron microscopy (TEM). The influence of pH, dilution, surfactant concentration and ionic strength on average particle size of pure and nutraceutical (benzylisothiocyanate and curcumin) encapsulated emulsion was examined. The prepared emulsion exhibited good stability up to 90 days in salt solution (50–200 mM) and different pH conditions. The cumulative release % of benzylisothiocyanate and curcumin was found to be 50.29% in 36 h and 89.15% in 150 h respectively. The antioxidant activity of pure, benzylisothiocyanate, curcumin and cocktail (benzylisothiocyanate and curcumin) nanoemulsion was calculated with 2,2-diphenyl-1-picrylhydrazyl radical. The IC₅₀ value of different antioxidant showed that benzylisothiocyanate nanoemulsion acted as better antioxidant as compared to pure and curcumin encapsulated nanoemulsion. Also the cell viability of pure nanoemulsion was found to be 24% on hep G2 cell. The effect of UV light irradiation on curcumin and benzylisothiocyanate stability was carried out in different solvent conditions (water/ethanol and nanoemulsion). The degradation of curcumin by the impact of UV light was successfully controlled by trapping in NEm.     

Ultrasonic emulsification of food-grade nanoemulsion formulation and evaluation of its bactericidal activity

Basil oil (Ocimum basilicum) nanoemulsion was formulated using non-ionic surfactant Tween80 and water by ultrasonic emulsification method. Process of nanoemulsion development was optimized for parameters such as surfactant concentration and emulsification time to achieve minimum droplet diameter with high physical stability. Surfactant concentration was found to have a negative correlation with droplet diameter, whereas emulsification time had a positive correlation with droplet diameter and also with intrinsic stability of the emulsion. Stable basil oil nanoemulsion with droplet diameter 29.3 nm was formulated by ultrasonic emulsification for 15 min. Formulated nanoemulsion was evaluated for antibacterial activity against Escherichia coli by kinetics of killing experiment. Fluorescence microscopy and FT-IR results showed that nanoemulsion treatment resulted alteration in permeability and surface features of bacterial cell membrane.     

Ultrasound processed nanoemulsion: A comparative approach between resveratrol and resveratrol cyclodextrin inclusion complex to study its binding interactions,antioxidant activity and UV light stability

Resveratrol is a naturally occurring therapeutic molecule used for treatment of diseases caused by oxidative stress. This investigation elucidates the advantages of fabrication of size controlled resveratrol inclusion complex. This has been done by encapsulating resveratrol-cyclodextrin inclusion complex in a phospholipid stabilized nanoemulsion formulated by ultrasonication emulsification method. The prepared nanoemulsion has been compared with resveratrol encapsulated nanoemulsion system. The morphology of the resveratrol nanoemulsion and inclusion complex nanoemulsion have been observed using transmission electron microscopy with average size 20.41 ± 3.41 and 24.48 ± 5.70 nm respectively. The nanoemulsion showed good loading and release efficiency. The radical diminishing potential of resveratrol and its inclusion complex has been compared in nanoemulsion. The effect of UV irradiation (365 nm) on resveratrol in different solvent systems (ethanol, water and nanoemulsion) indicated that nanoemulsion prevents degradation of resveratrol. Efforts have also been made to explore the interactions between bovine serum albumin and resveratrol in nanoemulsion.     

Fabrication of polymeric nanocapsules from curcumin-loaded nanoemulsion templates by self-assembly

In this study, biodegradable polymeric nanocapsules were prepared by sequential deposition of food-grade polyelectrolytes through the self-assembling process onto the oil (medium chain triglycerides) droplets enriched with curcumin (lipophilic bioactive compound). Optimum conditions were used to prepare ultrasound-assisted nanoemulsions stabilized by octenyl-succinic-anhydride (OSA)-modified starch. Negatively charged droplets (−39.4 ± 1.84 mV) of these nanoemulsions, having a diameter of 142.7 ± 0.85 nm were used as templates for the fabrication of nanocapsules. Concentrations of layer-forming cationic (chitosan) and anionic (carboxymethylcellulose) biopolymers were optimized based on the mean droplet/particle diameter (MDD/MPD), polydispersity index (PDI) and net charge on the droplets/capsules. Prepared core–shell structures or nanocapsules, having MPD of 159.85 ± 0.92 nm, were characterized by laser diffraction (DLS), ζ-potential (ZP), atomic force microscopy (AFM), transmission electron microscopy (TEM) and confocal laser scanning microscopy (CLSM). Furthermore, physical stability of curcumin-loaded nanocapsules in suspension was determined and compared at different storage temperatures. This study may provide information regarding the formation of ultrasound-assisted polymeric nanocapsules from the nanoemulsion templates which could be helpful in the development of delivery systems for lipophilic food bioactives.     

Emulsification by high frequency ultrasound using piezoelectric transducer: Formation and stability of emulsifier free emulsion

Emulsifier free emulsion was developed with a new patented technique for food and cosmetic applications. This emulsification process dispersed oil droplets in water without any emulsifier. Emulsions were prepared with different vegetable oil ratios 5%, 10% and 15% (v/v) using high frequency ultrasounds generated by piezoelectric ceramic transducer vibrating at 1.7 MHz. The emulsion was prepared with various emulsification times between 0 and 10 h. Oil droplets size was measured by laser granulometry. The pH variation was monitored; electrophoretic mobility and conductivity variation were measured using Zêtasizer equipment during emulsification process. The results revealed that oil droplets average size decreased significantly (p < 0.05) during the first 6 h of emulsification process and that from 160 to 1 μm for emulsions with 5%, 10% and from 400 to 29 μm for emulsion with 15% of initial oil ratio.For all tested oil ratios, pH measurement showed significant decrease and negative electrophoretic mobility showed the accumulation of OH⁻ at oil/water interface leading to droplets stability in the emulsion. The conductivity of emulsions showed a decrease of the ions quantity in solution, which indicated formation of positive charge layer around OH⁻ structure. They constitute a double ionic layer around oil particles providing emulsion stability. This study showed a strong correlation between turbidity measurement and proportion of emulsified oil.     

Physicochemical characterization of black seed oil-milk emulsions through ultrasonication

The ultrasonic formation of stable emulsions of a bioactive material, black seed oil, in skim milk was investigated. The incorporation of 7% of black seed oil in pasteurised homogenized skim milk (PHSM) using 20 kHz high intensity ultrasound was successfully achieved. The effect of sonication time and acoustic power on the emulsion stability was studied. A minimum process time of 8 min at an applied acoustic power of 100 W was sufficient to produce emulsion droplets stable for at least 8 days upon storage at 4 ± 2 °C, which was confirmed through creaming stability, particle size, rheology and color analysis. Partially denatured whey proteins may provide stability to the emulsion droplets and in addition to the cavitation effects of ultrasound are responsible for the production of smaller sized emulsion droplets.     

Preparation of betulinic acid nanoemulsions stabilized by ω-3 enriched phosphatidylcholine

Bioactive compounds such as ω-3 fatty acids and terpenes, have been associated with beneficial health effects; however, their solubility in the gastrointestinal tract and its bioavailability in the body are low. Nanoemulsions offer a viable alternative to disperse lipophilic compounds and improve their dissolution, permeation, absorption and bioavailability. Enzyme modified phosphatidylcholine (PC) with ω-3 fatty acids was used as emulsifier to stabilize oil-in-water nanoemulsions generated using ultrasound device. These systems were used as carriers of betulinic acid, which has reported anti-carcinogenic activity. Phospholipase-catalyzed modification of PC allowed the incorporation of 50 mol% of ω-3 fatty acids. Formation variables such as oil type and ultrasound amplitude had effects on nanoemulsion characteristics. Incorporation of betulinic acid affected globule size; however, betulinic acid nanoemulsions below 200 nm could be prepared. The conditions under which betulinic acid nanoemulsions were obtained using the modified phosphatidylcholine with the smaller globule size (91 nm) were 10% PC, 25% glycerol, medium chain oil and 30% amplitude for 12 min in the sonicator. Storage temperature had an effect on the stability of the nanoemulsions, at 5 °C we observed the smallest growth in globule size. The use of olive oil decreased the globule size growth during storage of the nanoemulsion stabilized with modified phosphatidylcholine, although globule size obtained was greater than 200 nm. Medium pH had a significant effect on the nanoemulsions; alkaline pH values improved storage stability. These results provide useful information for using this type of carrier system on the formulation of products in the pharmaceutical or food industry.     

Optimization of ultrasound induced emulsification on the formulation of palm-olein based nanoemulsions for the incorporation of antioxidant β-d-glucan polysaccharides

Polysaccharides of β-d-glucan configuration have well-known antioxidant activity against reactive free radicals generated from the oxidation of metabolic processes. In this study, β-d-glucan-polysaccharides extracted from Ganoderma lucidum were incorporated in palm olein based nanoemulsions which act as carrier systems to enhance the delivery and bioactivity of these polysaccharides and could be potentially useful for skin care applications. Initially response surface statistical design (Central Composite Design – CCD) was subjected to optimize the formulation variables of oil-in-water (O/W) nanoemulsions induced by ultrasound. The optimal formulation variables as predicted by CCD resulted in considerably improving the physical characteristics of ultrasonically formulated nanoemulsions by minimizing their droplet size, polydispersity index and viscosity. Moreover, the β-d-glucan-loaded nanoemulsions exhibited good stability over 90 days under different storage conditions (4 °C and 25 °C). The studies using palm olein based β-d-glucan-loaded nanoemulsion generated using ultrasound confirm higher antioxidant activity as compared to free β-d-glucan.     

Ultrasonically tailored,chemically engineered and “QbD” enabled fabrication of agomelatine nanoemulsion; optimization,characterization, ex-vivo permeation and stability study

The objective of present study was to develop a nanoemulsion formulation of agomelatine (BCS class II drug) for the solubility enhancement. Capmul MCM, Tween 80 and PEG-400 were selected as oil, surfactant and co-surfactant respectively. The high energy ultrasonication method was used for the preparation of nanoemulsion. Three-factor three-level central composite design was employed to get the best formulation. The independent variables selected for the optimization were % oil, %S_mix and sonication time (second). Based on the constraints applied to independent and dependent variables, the optimized formulation was selected with 2% oil, 10% S_mix and 45 s sonication time. The experimental values for dependent variables such as hydrodynamic diameter (nm), % transmittance and % CDR were found to be 73.72 ± 2.53 nm, 98.2 ± 0.42%, 84.71 ± 4.05% respectively. TEM and AFM−assisted morphological characterization of optimized Ago-NE was done and it was found with a spherical shape. The PDI, Zeta potential and the refractive index of optimized Ago-NE were found to be 0.137 ± 0.016, −7.40 ± 0.12 mV and 1.423 ± 0.045 respectively. The viscosity, pH and drug content of optimized Ago-NE were found as 25.12 ± 0.67 cP, 6.4 ± 0.17 and 97.83 ± 1.03% respectively. The ex-vivo permeation profile of optimized Ago-NE and agomelatine suspension through goat nasal mucosa were compared till 12 h and % cumulative drug permeated was found to be 90% and 40% respectively. The higher drug permeation profile of optimized Ago-NE confirmed that the solubility of agomelatine has been improved.     

Ultrasonic energy input influence οn the production of sub-micron o/w emulsions containing whey protein and common stabilizers

Ultrasonication may be a cost-effective emulsion formation technique, but its impact on emulsion final structure and droplet size needs to be further investigated. Olive oil emulsions (20 wt%) were formulated (pH ～ 7) using whey protein (3 wt%), three kinds of hydrocolloids (0.1–0.5 wt%) and two different emulsification energy inputs (single- and two-stage, methods A and B, respectively). Formula and energy input effects on emulsion performance are discussed. Emulsions stability was evaluated over a 10-day storage period at 5 °C recording the turbidity profiles of the emulsions. Optical micrographs, droplet size and viscosity values were also obtained. A differential scanning calorimetric (DSC) multiple cool–heat cyclic method (40 to ?40 °C) was performed to examine stability via crystallization phenomena of the dispersed phase.Ultrasonication energy input duplication from 11 kJ to 25 kJ (method B) resulted in stable emulsions production (reduction of back scattering values, dBS ～ 1% after 10 days of storage) at 0.5 wt% concentration of any of the stabilizers used. At lower gum amount samples became unstable due to depletion flocculation phenomena, regardless of emulsification energy input used. High energy input during ultrasonic emulsification also resulted in sub-micron oil-droplets emulsions (D₅₀ = 0.615 μm compared to D₅₀ = 1.3 μm using method A) with narrower particle size distribution and in viscosity reduction.DSC experiments revealed no presence of bulk oil formation, suggesting stability for XG 0.5 wt% emulsions prepared by both methods. Reduced enthalpy values found when method B was applied suggesting structural modifications produced by extensive ultrasonication. Change of ultrasonication conditions results in significant changes of oil droplet size and stability of the produced emulsions.     

EHD atomization characteristics of a point-plate system with a porous point electrode

An electrohydrodynamic (EHD) atomization from a point-to-plate system, with a wet porous point as a corona electrode, has been studied. And the atomized water droplets from the wet porous point, as well as the water droplet traces, the water droplet charge-to-mass ratios, and the water droplet number concentrations, were investigated. It was observed that the wet porous point can atomize abundant amounts of water droplet, 2.8, 2.6 and 2.2 mg/min for negative, AC and positive corona, respectively. The migrated water droplet traces were observed. The positive wet porous point atomized very fine water droplets than those obtained with the negative wet porous point. Moreover, the water droplets atomized from the AC corona showed granular-like larger traces. A weak corona discharge can atomize water droplets very effectively. On the other hand, an intensive corona discharge can eject more water droplets. As a result with the wet porous point, the maximum corona-current-based and corona-power-based water droplet atomization yields of Y_C = 3.34, 3.32 and 3.25 μg/μAs and Y_P = 0.35, 0.40 and 0.27 mg/Ws have been obtained for the negative, AC and positive corona discharges.     

Simulation of phase separation with large component ratio for oil-in-water emulsion in ultrasound field

This paper presents an exploration for separation of oil-in-water and coalescence of oil droplets in ultrasound field via lattice Boltzmann method. Simulations were conducted by the ultrasound traveling and standing waves to enhance oil separation and trap oil droplets. The focus was to the effect of ultrasound irradiation on oil-in-water emulsion properties in the standing wave field, such as oil drop radius, morphology and growth kinetics of phase separation. Ultrasound fields were applied to irradiate the oil-in-water emulsion for getting flocculation of the oil droplets in 420 kHz case, and larger dispersed oil droplets and continuous phases in 2 MHz and 10 MHz cases, respectively. The separated phases started to rise along the direction of sound propagation after several periods. The rising rate of the flocks was significantly greater in ultrasound case than that of oil droplets in the original emulsion, indicating that ultrasound irradiation caused a rapid increase of oil droplet quantity in the progress of the separation. The separation degree was also significantly improved with increasing frequency or irradiation time. The dataset was rearranged for growth kinetics of ultrasonic phase separation in a plot by spherically averaged structure factor and the ratio of oil and emulsion phases. The analyses recovered the two different temporal regimes: the spinodal decomposition and domain growth stages, which further quantified the morphology results. These numerical results provide guidance for setting the optimum condition for the separation of oil-in-water emulsion in the ultrasound field.