Large Emulsion Droplets Research Articles

Adsorption and inhibition of lipid oxidation of curcumin embeded egg ovalbumin/ sodium carboxymethylcellulose nanoparticles at the oil-in water interface

In this study, the adsorption and inhibition of lipid oxidation propertises of curcumin embeded ovalbumin (OVA)/sodium carboxymethylcellulose (CMC) were investigated. The results demonstrated that the adsorption of curcumin and OVA/CMC particles at the oil-water interface might form a dual protection. The larger emulsion droplets were formed at an OVA/CMC ratio of 1:2 (pH 4.4) due to bridging flocculation. In the other two ratios (1:1, 2:1), the emulsions showed good stability after 32 days of storage. At the ratios of 1:2, 1:1, and 2:1, the oxidation rate of the oil in the emulsion stabilized by OVA/CMC and OVA/CMC-Cur particles reduced by 16.2% and 37.9%, 4.9% and 38.9%, and 8.8% and 35.8%, respectively, than the pure oil. At the ratios of 1:1 and 2:1, the emulsion stabilized by the OVA/CMC-Cur particles demonstrated excellent antioxidant resistance and storage stability, particularly at the ratio of 1:1.

Studying the photothermal activation of polydopamine-shelled, phase-change emulsion droplets into microbubbles using small- and ultra-small-angle neutron scattering

Polydopamine-shelled perfluorocarbon (PDA/PFC) emulsion droplets are promising candidates for medical imaging and drug delivery applications. This study investigates their phase transition into microbubbles under near-infrared (NIR) illumination in situ using small- and ultra-small-angle neutron scattering (SANS and USANS) and contrast variation techniques. Supported by optical microscopy, thermogravimetric analysis, and ultrasound imaging, SANS and USANS results reveal rapid phase transition rates upon NIR illumination, dependent on PFC content and droplet size distribution. Specifically, perfluoropentane droplets rapidly transform into bubbles upon NIR irradiation, whereas perfluorohexane droplets exhibit greater resistance to phase change (bulk boiling points = 30 °C and 60 °C, respectively). Furthermore, smaller emulsion droplets with unimodal distribution resist NIR-triggered phase changes better than their bimodal counterparts. This observation is attributable to the lower boiling points of large emulsion droplets (lower Laplace pressure than smaller droplets) and the faster photothermal heating rates due to their thicker polydopamine shells. The insights gained from these techniques are crucial for designing phase-change emulsions activated by NIR for photothermal therapies and controlled drug delivery.

Self-healing waterborne polyurethane coatings with high transparence and haze via cellulose nanocrystal stabilized linseed oil Pickering emulsion

Protection coatings with self-healing ability can significantly enhance their anti-corrosion properties and service life. In this study, self-healing waterborne polyurethane (WPU) coatings with high transparence and haze were facile fabricated via cellulose nanocrystal (CNC) stabilized linseed oil (LO) Pickering emulsion. Sustainable CNCs displayed outstanding emulsifying ability and stability to stabilize LO Pickering emulsion. The size of LO Pickering emulsion droplets decreases with the CNC concentration, while the emulsion fraction and surface coverage by CNCs increase with CNC concentration, leading to a more stable Pickering emulsion. The self-healing rates of WPU coatings at varied time, temperature, CNC and catalyst concentration were investigated. Higher temperature, larger emulsion droplets, and with driers employed as catalysts generally lead to faster self-healing rate. The WPU self-healing coatings displayed much better abrasion resistance and mechanical properties than pristine WPU due to the incorporation of CNCs. Moreover, the WPU self-healing coatings show a high transparence and haze due to light scattering, and their applications as coatings of lamp covers and glass to achieve uniform light distribution and privacy protection with high light transmission were further demonstrated.

Water-in-Water Emulsions, Ultralow Interfacial Tension, and Biolubrication

Water-in-Water Emulsions, Ultralow Interfacial Tension, and Biolubrication

Micro-explosion of droplets containing liquids with different viscosity, interfacial and surface tension

Micro-explosion and puffing of multi-component slurry and emulsified fuel droplets can provide a several-fold increase in the evaporation and chemical reaction surface area. As a result, micro-explosion and puffing shorten the heating, evaporation, and ignition time of fuel compositions, improve the efficiency of their combustion, reduce fuel consumption, and provide its smooth spraying in combustion chambers. There are still no thorough studies on how the viscosity as well as surface and interfacial tension of emulsified fuels affect the integral characteristics of micro-explosive breakup of droplets under intense heating. In certain ranges of temperatures and component concentrations, there may be synergistic effects of these fuel characteristics on the threshold conditions and outcomes of micro-explosive droplet atomization. Such synergistic effects can make the secondary atomization of fuel droplets much more effective. In this research, we experimentally determine the heating times until breakup of relatively large emulsion droplets, the size and velocity distributions of newly formed child droplets with varying heating temperature, initial size of parent droplets, as well as component type and concentration. The results of this research are important for developing the current micro-explosion models and creating new, accounting for the breakup mechanisms and outcomes.

Effects of hydrosoluble calcium ions and organic acids on citrus oil emulsions stabilized with citrus pectin

Citrus fruits are rich in nutritional substances, including various hydrosoluble and liposoluble components, and many of these are subject to enormous waste in the food industry. To make full use of these components and produce novel, high value-added citrus products, an emulsion-based delivery system containing both hydrosoluble (Ca2+, citric acid, ascorbic acid, and citrus pectin) and liposoluble (citrus oil) components was fabricated. In this paper, we investigated the effects of hydrosoluble calcium ions and organic acids on the properties and stability of citrus oil emulsions stabilized by citrus pectin. The effects of varying the adding order of Ca2+ and organic acids were analyzed for the first time. Ca2+ can interact with citrus pectin, resulting in large emulsion droplets. Adding Ca2+ prior to emulsification resulted in an emulsion that was stable with respect to phase separation for 20 days, due to the enhancement of the continuous phase viscosity. The addition of organic acids (citric acid and ascorbic acid) reduced the droplet size and improved the emulsion stability, and the benefits were more evident when acids were added prior to emulsification (from 1.47 to 0.83 μm with 1 wt% ascorbic acid added), due to the enhancement of the emulsifying capacity caused by the acidic environment. Notably, the degradation of d-limonene was reduced by adding 1 wt% ascorbic acid to the citrus oil emulsion. Furthermore, the large droplets formed due to the addition of Ca2+ can be avoided by the simultaneous addition of organic acid. This study details a novel emulsion product prepared using endogenous citrus nutrient components, which may improve the utilization and added value of citrus fruits.

Kinetic stability of surfactant stabilized water-in-diesel emulsion fuels

Commercialization of water-in-diesel emulsion fuels demand investigation of the stability of the emulsions over extended periods of time during their storage in the fuel tank as well as during the engine operation. A detailed analysis of the stability of water-in-diesel emulsion fuels stabilized by a mixture of commercially available surfactants is presented. The hydrophile lipophile balance (HLB) is varied by changing the relative composition of the surfactants, Span®80 and Tween®80, and its influence on the microstructure of the formulations is explored using bright field optical microscopy. Emulsions with smaller droplet sizes can be formulated at intermediate compositions of the mixed surfactant system. The effect of surfactant concentration is investigated using microscopy and dynamic light scattering. At 10% surfactant concentration, the emulsification leads to the formation of nanoemulsions containing water droplets of diameter as small as 159 nm. Finally, time stability of emulsions formed at various surfactant concentrations is investigated. Emulsions formed at 2% and 5% surfactant concentration reveal a macroscopic phase separation of initially homogeneous emulsions into phases containing large emulsion droplets in the bottom phase and smaller emulsion droplets in the top phase. In contrast, the emulsions formed at 10% surfactant concentration, show enhanced time stability, with no macroscopic phase separation, although the droplet size increases from 159 nm to 330 nm upon 50 days of storage. An understanding of the change in microstructure and droplet size as a function of time presented in this work is crucial for the systematic investigation of use of such fuels in practical applications.

Effects of deodorization by powdered activated carbon, β-cyclodextrin and yeast on odor and functional properties of tiger puffer (Takifugu rubripes) skin gelatin

The study investigated odor, physiochemical and functional properties of tiger puffer skin gelatin (TPSG) deodorized by powdered activated carbon (PAC, 0.5%), β-cyclodextrin (βCD, 3%) and yeast fermentation (YEF, 1%). Sensory test and electronic nose analysis exposed that three treatments lowered fishy odor intensity, coincided with decreased categories and levels of volatile compounds. Amide I, II and B of group βCD were shifted to lower wavenumber and amplitudes of amide bands in group YEF were much lower than those of others. Gel strength of group βCD and YEF declined, coincided with their higher relaxation time (component T22 and T2b) (p < 0.05). Marked decreases in gelling and melting temperature were found in group βCD. Emulsion activity index of group YEF decreased (p < 0.05) while emulsion stability index of all deodorized groups increased (p < 0.05). Different from uneven clusters with large size emulsion droplets in control, a homogenous system with small size droplets was observed in group YEF. PAC filtration increased clarity and lowered b* value (p < 0.05), but βCD treatment greatly decreased clarity (p < 0.05). Results suggest that YEF and βCD treatment deteriorated physical and functional properties of TPSG. Nevertheless, PAC filtration reduced fishy odor without compromising physiochemical and functional properties and is recommended for TPSG deodorization.

Porous Gelatin Membrane Obtained from Pickering Emulsions Stabilized by Graphene Oxide.

This article presents a novel procedure for preparing porous membranes from water-soluble polymers involving the formation of a Pickering emulsion. Gelatin is a biodegradable biopolymer obtained by the partial hydrolysis of collagen. A biopolymer such as gelatin is capable of adsorbing at an oil/water interface, resulting in decreased interfacial energy. Hence, gelatin is widely employed as an alternate for synthetic surfactants to stabilize emulsions in the food industry. However, high-molecular-weight gelatin leads to large emulsion droplets and poor emulsion stability. The amphoteric nature of graphene oxide (GO) nanosheets was helpful in stabilizing the oil/water interface and allows for the preparation of a stable gelatin/GO emulsion. Membranes fabricated using gelatin/GO have a uniformly distributed porous structure. However, prepared membranes are highly hydrosoluble, so the membranes were cross-linked without affecting their morphology. XRD results evidenced that gelatin effectively exfoliated the graphite oxide which is essential to stabilizing the emulsion. Fabricated gelatin/GO membranes possess uniformly distributed pores and are highly stable in aqueous solution. Pure water filtration tests were conducted on the membranes. The permeability results proved that the membranes fabricated by a Pickering emulsion are promising materials for filtration.

Evidence of coexisting microemulsion droplets in oil-in-water emulsions revealed by 2D DOSY 1H NMR

Optimizing the macroscopic properties, shelf-life and stability of emulsion products requires a better understanding of the microstructural characteristics such as the type (nano, micro and macro) and the relative distribution of components (i.e., oil and surfactant) within the emulsion droplets. We used Diffusion-Ordered NMR Spectroscopy (DOSY NMR) to evaluate these characteristics in model oil-in-water emulsion containing Tween 80 and medium chain triglycerides (MCT). At low MCT concentrations, the solutions were transparent but from 1 to 5 wt% MCT, they became translucent then opaque. 1 wt% MCT was the upper boundary for the appearance of nanoemulsion phase. From the decays of the chemical shift signals of MCT and Tween 80, the DOSY results clearly demonstrate that the self-diffusion coefficients (D) are dependent on oil concentration. Small microemulsion droplets of almost uniform size (d = 12–22 nm) coexist with two sets of large nanoemulsion (d < 200 nm) and emulsion (d > 200 nm) droplets. The large droplets increase significantly in size with increasing MCT. The most striking result is the clear evidence for the presence of microemulsion droplets of nearly uniform size in the aqueous phase from below to above the nanoemulsion transition concentration at 1 wt% MCT.

Spontaneous and Flow-Driven Interfacial Phase Change: Dynamics of Microemulsion Formation at the Pore Scale.

The dynamic behavior of microemulsion-forming water-oil-amphiphiles mixtures is investigated in a 2.5D micromodel. The equilibrium phase behavior of such mixtures is well-understood in terms of macroscopic phase transitions. However, what is less understood and where experimental data are lacking is the coupling between the phase change and the bulk flow. Herein, we study the flow of an aqueous surfactant solution-oil mixture in porous media and analyze the dependence of phase formation and spatial phase configurations on the bulk flow rate. We find that a microemulsion forms instantaneously as a boundary layer at the initial surface of contact between the surfactant solution and oil. The boundary layer is temporally continuous because of the imposed convection. In addition to the imposed flow, we observe spontaneous pulsed Marangoni flows that drag the microemulsion and surfactant solution into the oil stream, forming large (macro)emulsion droplets. The formation of the microemulsion phase at the interface distinguishes the situation from that of the more common Marangoni flow with only two phases present. Additionally, an emulsion forms via liquid-liquid nucleation or the Ouzo effect (i.e., spontaneous emulsification) at low flow rates and via mechanical mixing at high flow rates. With regard to multiphase flow, contrary to the common belief that the microemulsion is the wetting liquid, we observe that the minor oil phase wets the solid surface. We show that a layered flow pattern is formed because of the out-of-equilibrium phase behavior at high volumetric flow rates (order of 2 m/day) where advection is much faster than the diffusive interfacial mass transfer and transverse mixing, which promote equilibrium behavior. At lower flow rates (order of 30 cm/day), however, the dynamic and equilibrium phase behaviors are well-correlated. These results clearly show that the phase change influences the macroscale flow behavior.

Investigation of the fabrication and subsequent emulsifying capacity of potato protein isolate/κ-carrageenan electrostatic complexes

The fabrication of protein-polysaccharide complexes via electrostatic interactions was investigated with a naturally cationic protein, potato protein isolate (PoPI), and an anionic polysaccharide, κ-carrageenan (κC), at unadjusted pH conditions. Moreover, the emulsifying capacity of these electrostatic complexes (PoPI-κC) was assessed. PoPI-κC complexes were prepared with a fixed concentration of PoPI (1 wt %), and varying concentrations of κC (0.01–0.5 wt %), using gentle agitation, followed by sonication to fabricate the complexes. The physicochemical properties of PoPI-κC complexes was assessed in terms of size and surface charge, measured using light scattering techniques and electrokinetic potential, respectively. The emulsifying performance of emulsions prepared with PoPI-κC complexes was assessed as a function of κC, and to PoPI, with respect to initial emulsion droplet size, emulsion stability, interfacial tension and optical microscopy.Addition of κC to a 1 wt % PoPI solution yielded the formation of submicron (∼120 nm) electrostatic complexes up to a κC concentration of ≤0.0375 wt %. Higher concentrations of κC yielded micron sized complexes (>10 μm). Emulsions prepared with PoPI-κC complexes yielded comparable emulsion droplet sizes to that of PoPI alone, with the exception of complexes prepared with κC in the range of 0.05–0.07 wt %. Larger emulsion droplets were observed, as these complexes possessed an electrokinetic potential close to the isoelectric point, resulting in aggregation. Emulsions prepared with PoPI-κC complexes possessed marginally enhanced long-term stability in comparison to emulsions prepared with PoPI alone.

Designing W 1/O/W 2 double emulsions stabilized by protein–polysaccharide complexes for producing edible films: Rheological, mechanical and water vapour properties

Rheological properties and the droplet mean volume-surface diameter of water-in-oil-in-water double emulsions E LMP–WPI and E CMC–WPI, stabilized with low-methoxyl pectin (LMP)–whey protein isolate (WPI) or sodium carboxymethylcellulose (CMC)–WPI complexes were determined. E LMP–WPI emulsions showed smaller droplet diameter (2.47 μm) than E CMC–WPI emulsions (10.68 μm), and higher values of apparent viscosity, storage modulus and loss modulus. Microstructure and mechanical properties of the F LMP–WPI and F CMC–WPI films were affected by the type of the stabilizing biopolymer complex used in the formulation of the E LMP–WPI and E CMC–WPI double emulsions from which were prepared. The F LMP–WPI films microstructure consisted of a biopolymer mainframe relatively compact, interrupted by small emulsion droplets. The F CMC–WPI film mainframe had an open and oriented structure, in which relatively large emulsion droplets were packed. F LMP–WPI films presented higher values of transparency, tensile strength and Young’s modulus, but lower elongation percentage and comparable water vapour permeability than F LMP–WPI films.

Drying of Complex Suspensions

We investigate the 3D structure and drying dynamics of complex mixtures of emulsion droplets and colloidal particles, using confocal microscopy. Air invades and rapidly collapses large emulsion droplets, forcing their contents into the surrounding porous particle pack at a rate proportional to the square of the droplet radius. By contrast, small droplets do not collapse, but remain intact and are merely deformed. A simple model coupling the Laplace pressure to Darcy's law correctly estimates both the threshold radius separating these two behaviors, and the rate of large-droplet evacuation. Finally, we use these systems to make novel hierarchical structures.

Flow Cytometry as a New Approach To Investigate Drug Transfer between Lipid Particles

Lipid nanoparticles and liposomal carrier systems are of growing interest for intravenous drug delivery due to their biocompatibility and targetability. It is, however, difficult to investigate their release behavior for lipophilic drugs under physiological conditions. This study describes a novel flow cytometric method studying drug transfer from such carrier systems to particles simulating physiological receptor sites. For this purpose, liquid and solid trimyristin nanoparticles or soybean phospholipid liposomes were loaded with the lipophilic fluorescent substances Nile red, temoporfin, and DiI. The transfer of these model drugs to large emulsion droplets was examined by flow cytometry. Transfer of DiI to differently sized acceptor emulsions was also monitored by separating donor and acceptor particles using ultracentrifugation. Flow cytometry revealed a completion of transfer within a few minutes for Nile red and temoporfin at considerable amounts of transferred dye. In contrast, the highly lipophilic DiI transferred over a period of weeks only for a small percentage of the dye. Ultracentrifugation results confirmed this for DiI and indicated a dependence of transfer characteristics on the acceptor surface area. Nile red transfer into a bulk oil phase as alternative acceptor system was also very slow. Flow cytometry seems to be well suited to study the intrinsic transfer of fluorescent lipophilic substances, as no kinetic hindrances like dialysis bags nor separation steps are required. Additional detailed experiments will, however, be necessary to elucidate the prevalent transfer mechanisms completely.

In Vitro Characterization and Mosquito (Aedes aegypti) Repellent Activity of Essential-Oils-Loaded Nanoemulsions

The nanoemulsions composed of citronella oil, hairy basil oil, and vetiver oil with mean droplet sizes ranging from 150 to 220 nm were prepared and investigated both in vitro and in vivo. Larger emulsion droplets (195-220 nm) shifted toward a smaller size (150-160 nm) after high-pressure homogenization and resulted in higher release rate. We proposed that thin films obtained from the nanoemulsions with smaller droplet size would have higher integrity, thus increasing the vaporization of essential oils and subsequently prolonging the mosquito repellant activity. The release rates were fitted with Avrami's equations and n values were in the same range of 0.6 to 1.0, implying that the release of encapsulated limonene was controlled by the diffusion mechanism from the emulsion droplet. By using high-pressure homogenization together with optimum concentrations of 5% (w/w) hairy basil oil, 5% (w/w) vetiver oil (5%), and 10% (w/w) citronella oil could improve physical stability and prolong mosquito protection time to 4.7 h due to the combination of these three essential oils as well as small droplet size of nanoemulsion.

Influence of emulsion and powder size on the stability of encapsulated d-limonene by spray drying

The microencapsulation of d-limonene by spray drying was investigated with respect to the effects of emulsion droplet size, powder particle size, as well as to the effects of various kinds of matrices (gum arabic, maltodextrin, and modified starch) on its stability. It was realized by studying release characteristics and oxidative stability during storage. The release and the oxidation decreased deeply with an increase in powder and emulsion particle size for gum arabic and maltodextrin materials. Further, the distributions of emulsion size in the powder showed an increase in the fraction of large emulsion droplets and changed to a bimodal distribution. However, the modified starch HI-CAP 100 showed a higher stability of encapsulated d-limonene than the others. The influence of powder and emulsion size on its encapsulated flavor as well as the change in the emulsion size during storage could not be observed. Industrial Relevance Spray drying is a common and useful unit operation for microencapsulation of food ingredients. Data on emulsion droplet size and on powder size on product stability provide conflicting results which makes a systematic study regarding these factors highly relevant. The data suggest that an optimal size of flavour powder should be selected for high retention during spray drying, stability during storage and for the ability to control release of flavour.

Influence of Bulk Elasticity and Interfacial Tension on the Deformation of Gelled Water-in-Oil Emulsion Droplets: An AFM Study

We used atomic force microscopy (AFM) to study the deformation and wetting behavior of large (50-250 microm) emulsion droplets upon mechanical loading with a colloidal glass probe. Our droplets were obtained from water-in-oil emulsions. By adding gelatin to the water prior to emulsification, also droplets with a bulk elasticity were prepared. Systematic variations of surfactant and gelatin concentrations were made, to investigate their effect on the deformation and wetting behavior of the droplets and to identify the contributions of interfacial tension, bulk elasticity, and expelled water. The AFM experiments were performed in force--distance mode and showed on approach a repulsive regime which in many cases was terminated by a jump-in of the probe. In the case of pure water (i.e. gelatin-free) droplets, the repulsive part of the curve showed a good linearity, thus allowing the extraction of an effective droplet spring constant. This quantity was found to decrease on raising the surfactant concentration from below the critical micelle concentration (cmc) to well above the cmc, and its numerical values were found to correspond remarkably well to literature values for the interfacial tension. Our findings indicate that, on gelatin increase inside the droplets, the bulk elasticity gradually becomes dominant and the droplets' stiffness does not depend anymore on surfactant concentration. Also the stability of the droplet interface against wetting, as measured by the force at which the jump-in instability occurs, was enhanced by gelatin. For gelatin concentrations of > or =15 wt %, the droplets were found to behave like purely elastic bodies. Both gelatin and surfactant contribute positively to the stability against interface breakup.

Emulsion properties of casein and whey protein hydrolysates and the relation with other hydrolysate characteristics.

Casein and whey protein were hydrolyzed using 11 different commercially available enzyme preparations. Emulsion-forming ability and emulsion stability of the digests were measured as well as biochemical properties with the objective to study the relations between hydrolysate characteristics and emulsion properties. All whey protein hydrolysates formed emulsions with bimodal droplet size distributions, signifying poor emulsion-forming ability. Emulsion-forming ability of some casein hydrolysates was comparable to that of intact casein. Emulsion instability was caused by creaming and coalescence. Creaming occurred mainly in whey hydrolysate emulsions and in casein hydrolysate emulsions containing large emulsion droplets. Coalescence was dominant in casein emulsions with a broad particle size distribution. Emulsion instability due to coalescence was related to apparent molecular weight distribution of hydrolysates; a relative high amount of peptides larger than 2 kDa positively influences emulsion stability.

Production of porous suspension polymer beads with a narrow size distribution using a cross-flow membrane and a continuous tubular reactor

The work described focuses on a two-stage process for the production of large porous suspension polymer beads of defined particle size and narrow size distribution. Emulsification has been performed using purpose built cross-flow membrane equipment, which allows controlled production of large emulsion droplets with a much narrower size distribution. The work described compares the production of large emulsion droplets of monomer prepared both by agitation and using a cross-flow membrane. The effects of variations in the pore size of the membrane and flow-rates on the size of the emulsion droplets produced are also investigated. The second stage of the process is polymerisation of performed monomer emulsion droplets using a continuous tubular reactor. Samples polymerised using such a method show a narrower size distribution than similar systems polymerised as a batch.