Surface Of Emulsion Droplets Research Articles

The heat stability of Rhamnolipid containing egg-protein stabilised oil-in-water emulsions

The heat stability of egg white stabilised emulsions was studied in the presence of monoglycerides, lecithin and rhamnolipid biosurfactants. Rhamnolipids have a greater effect on the reduction of emulsion droplet particle size than either lecithin or monoglycerides, with both the latter having virtually no effect even at high concentration. The effect of all surfactants on heat stability is concentration dependent. There is trend towards a minimum in heat stability (represented by the first order rate constant, k) for emulsions stabilised by all surfactants at a molar ratio (R) of egg protein to surfactant of R = 50 for monoglycerides, R = 34 for lecithin and R = 61 for rhamnolipids. However, this trend is only statistically significant for the rhamnolipid emulsions. The largest decrease in heat stability is observed for the rhamnolipid stabilised emulsion. The rhamnolipid biosurfactant is also the only one of the three surfactants that is able to provide heat stability to the emulsion at high molar ratios, presumably due to competitive displacement of the protein from the emulsion droplet surface. Analysis of the thermodynamics of the heat-induced destabilization of the emulsions suggests differing mechanisms for the three surfactants, probably related to the way in which the different surfactants interact with the adsorbed protein layer. Molecular docking and molecular dynamics simulations confirm different binding affinity to egg proteins for the rhamnolipid and lecithin surfactants.

Bulk and Interfacial Contributions to Stabilization of Cyclodextrin-Based Emulsions Mediated by Bacterial Cellulose.

Cyclodextrin (CD)-based emulsions have a characteristic of rapid droplet flocculation, which limits their application as functional material templates, so it is very important to improve the stability of CD-based emulsions. In this study, we select bacterial cellulose (BC) as a nonadsorbing inhibitor to prevent flocculation of CD-based emulsions. We map a phase diagram of the aqueous dispersions of CD inclusion complexes (ICs) and BC from morphological observations and investigate the effects of BC on properties of the IC-laden films. We further explore the effects of BC concentration on the stability of the CD-based emulsions and investigate rheological behavior of the emulsions through large-amplitude oscillatory shear experiments. It shows that BC can effectively suppress the flocculation of CD-based emulsion droplets even at a concentration as low as 0.01 wt %. We propose that BC has dual effects from bulk and interfacial contributions on increasing emulsion stability. At low concentrations, BC mainly results in higher packing density of ICs on the emulsion droplet surface through excluded volume repulsion, and at high concentrations, BC creates a network structure that confines the motion of emulsion droplets and retards flocculation.

Stress buffering in cyclodextrin-based membranes coated on emulsion droplet surfaces.

Surface instability of membranes not only plays a critical role in the morphological evolution observed in natural and biological systems, but also underpins a promising way for the bottom-up fabrication of novel functional materials. There is an urgent need for the design of novel building blocks into membranes, and the understanding of the abilities of the membranes to cope with mechanical stress is therefore of considerable importance. Here, we design membranes built with cyclodextrin-oil inclusion complexes, which are formed spontaneously at the oil/water interface by a self-assembly process. We select the oil phases of distinct molecular structures, namely, branched triglyceride oil and straight-chain n-dodecane, and examine the patterns in which the membranes adopt morphological transitions to buffer stress. We discuss two possible buffering scenarios for the behaviors observed in view of structural arrest and interfacial rheology, which are most closely linked to the rigidity of the membranes. The membranes represent fascinating models and shed some light on the origin of arrested stress relaxation.

Effect of polyglycerol polyricinoleate concentrations on the adsorption behavior of hydroxyapatite nanoparticles at the oil-water interface of emulsion

The adsorption behavior of hydroxyapatite (HAp) nanoparticles at the oil-water interface is very important for the microstructure of organic-inorganic composite fabricated using HAp nanoparticles stabilized Pickering emulsion as template. Studies on its adsorption behavior have attracted much interest because of the importance for their applications in biomedical field. Emulsions with dichloromethane (CH2Cl2) dissolved poly(l-lactic acid) (PLLA) as the oil phase and hydroxyapatite (HAp) nanoparticles dispersed in deionized water as the aqueous phase were prepared with different polyglycerol polyricinoleate (PGPR) concentrations in order to obtain PLLA/HAp porous composite. The distribution of HAp nanoparticles at the oil-water interface with different PGPR concentrations were characterized by confocal laser scanning microscope, and the adsorption behavior of HAp nanoparticles was also discussed. Transmission electron microscope and cryo-scanning electron microscope were used to characterize the emulsion stabilized by HAp nanoparticles with PGPR concentration of 1.0 w/v%. The results indicated that HAp nanoparticles were dispersed on the surface of emulsion droplets to stabilize emulsion, and some of them were also distributed on the surface of emulsion droplets or adjacent emulsion droplets in the form of agglomerates with lower PGPR concentrations. HAp nanoparticles escaped from the oil-water interface to the oil phase with increasing PGPR concentrations, and PGPR became the main emulsion stabilizer. Pickering emulsion was changed into classical emulsion with increasing PGPR concentration because PGPR turned to be the main stabilizer instead of HAp nanoparticles. Both microspheres and porous materials were fabricated using the as-received emulsion as template. This work would be helpful to study the adsorption behavior of HAp nanoparticles as well as its effect on the emulsion properties.

Effect of calcium chloride on emulsion stability of methyl-esterified citrus pectin.

High methyl-esterified citrus pectin (HMCP) molecules could be self-assembled into micelles in water. The morphology of HMCP micelles in water was irregular spheres, long rods, and arc-shaped. Most of HMCP molecules cross-linked with HMCP micelles in the presence of calcium chloride and increased the range of size distribution of HMCP micelles. A little number of HMCP molecules cross-linked with each other to form 80 nn~200nm microgel particles. Calcium chloride could improve HMCP emulsification when its concentration was more than 70mmol/L. HMCP micelles could be adsorbed on the surface of emulsion droplets. The emulsion prepared with HMCP and calcium chloride was similar to the Pickering emulsion.

Mannose-Coated Fluorescent Lipid Microparticles for Specific Cellular Targeting and Internalization via Glycoreceptor-Induced Phagocytosis.

In this work, we report on the development of mannose-coated fluorescent lipid microparticles to study the role of C-type lectin membrane receptors in phagocytosis. The micrometric droplets of soybean oil-in-water emulsion were functionalized with a tailor-made fluorescent mannolipid. The amphiphilic ligand was built from a mannose unit, a lipid C11 spacer, and a naphthalimide fluorophore. The functionalization of the droplets was monitored by fluorescence microscopy as well as their interaction with concanavalin A, which was used as a model lectin in vitro. The use of a monovalent ligand on the surface of emulsion droplets yielded particles with an affinity approximately 40 times higher than that of free mannose. In cellulo, the coated droplets were shown to be specifically internalized by macrophages in a receptor-dependent phagocytic pathway. The naked droplets, on the other hand, displayed very little internalization because of their low immunogenicity. This work thus brings evidence that C-type lectin membrane receptors may act as phagocytic receptors. The functionalization of the droplets with the tailored amphiphilic fluorescent ligand also provides insights into the development of organic fluorescent particles that may prove useful for developing targeted imaging and delivery tools.

Transparent and strong polymer nanocomposites generated from Pickering emulsion gels stabilized by cellulose nanofibrils

We report here the development of transparent and strong polymer composites reinforced by unmodified cellulose nanofibrils (CNFs) with a Pickering emulsion gelation strategy. The CNFs entangle and firmly stabilize on the surface of emulsion droplets containing polymethyl methacrylate (PMMA) solution, leading to the gelation of the emulsions. CNFs/PMMA composites were generated via vacuum filtration and solvent washing of the gel and a subsequent two-step hot pressing. The composites contained a unique self-assembled two-tier hierarchy of CNFs networks and demonstrate promising transparency, tensile strength, flexibility, and an extremely low thermal expansion. Remarkably, these properties are highly tunable with varying the concentration of CNFs and the volume ratio of the water to oil phase. This work offers a facile route to realize the well dispersion of unmodified CNFs in hydrophobic polymer matrix and achieve high performance of polymeric materials reinforced by CNFs.

Study on Stability and Stability Mechanism of Styrene-Acrylic Emulsion Prepared Using Nanocellulose Modified with Long-Chain Fatty Acids.

In this study, nanocrystalline cellulose (NCC) was grafted with lauric acid, palmitic acid, and stearic acid and used as stabilizer to prepare styrene butyl acrylate emulsion. The properties of the emulsion were determined, and the mechanism of modified NCC (MNCC) stabilized emulsion was analyzed. Results showed that long-chain fatty acids were grafted to NCC through esterification initiated at a low temperature. When the dosage of L-MNCC, P-MNCC, and S-MNCC was 0.05%, the styrene-acrylic emulsion had 92.5%, 94.2%, and 96.3% conversion rates, respectively, and exhibited good dilution, pH, Ca2+, and centrifugal stability. The particle size of styrene-acrylic emulsion was approximately 460 nm, and the absolute value of the Zeta potential increased with the MNCC concentration. According to the images of optical microscopy and the transmission electron microscope, the MNCC was adsorbed onto the surface of styrene-acrylic emulsion droplets. The synergistic effect from the electrostatic repulsion of MNCC, the hydrophile lipophilicity of MNCC, and the spatial hindrance of the MNCC adsorption layer provided good stability for the styrene-acrylic emulsion. Therefore, MNCC could replace traditional surfactants in stabilizing emulsion.

Magnetically responsive Janus nanoparticles synthesized using cellulosic materials for enhanced phase separation in oily wastewaters and water-in-crude oil emulsions

A new class of magnetically responsive and interfacially active Janus (M−Janus) nanoparticles was designed and synthesized by sequential adsorption of cellulosic materials: hydrophobic ethyl cellulose (EC) and hydrophilic carboxymethyl cellulose (CMC) on the opposite sides of magnetite (Fe3O4) nanoparticles. The adsorption study using quartz crystal microbalance with dissipation (QCM-D) proved the concept of proposed synthesis of M−Janus nanoparticles. The adsorption of EC and CMC on magnetite nanoparticles was confirmed by zeta-potential measurements, thermogravimetric analysis (TGA), characterization using Fourier transform infrared spectroscopy (FTIR) and TEM. The surface wettabilities of the opposite sides on the M−Janus nanoparticles were investigated by measuring contact angles of nanoparticle surfaces deposited from the oil-water interfaces using the Langmuir-Blodgett method. SEM images revealed an excellent dispersion of M−Janus nanoparticles in both aqueous and organic phases. The results from the coalescence time and crumpling ratio measurement of particles-stabilized oil droplets along with the interfacial pressure-area isotherms demonstrated stronger interfacial activities of M−Janus nanoparticles and a stiffer interface with adsorbed M−Janus nanoparticles as compared with the interfaces stabilized by conventional interfacially-active nanoparticles. The microscopy images confirmed the deposition of M−Janus nanoparticles at the emulsion droplet surface during the phase separation process. The M−Janus nanoparticles not only exhibited excellent capability and high efficiency in separating emulsified water from water-in-crude oil emulsions and the oil from oily wastewaters under an external magnetic field, but also retained high interfacial activity and hence desirable separation efficiency after five-cycle applications. Because of the environmentally friendly and biodegradable cellulosic materials used in the synthesis, the M−Janus nanoparticle can achieve effective oil/water phase separation without causing further pollution to the continuous phase.

Encapsulation of Emulsion Droplets with Metal Shells for Subsequent Remote, Triggered Release.

A two-step method to encapsulate an oil core with an impermeable shell has been developed. A thin metallic shell is deposited on the surface of emulsion droplets stabilized by metal nanoparticles. This thin shell is shown to prevent diffusion of the oil from within the core of the metal-shell microcapsules when placed in a continuous phase that fully dissolves the oil. The stabilizing nanoparticles are sterically stabilized by poly(vinyl pyrrolidone) chains and are here used as a catalyst/nucleation site at the oil-water interface to grow a secondary metal shell on the emulsion droplets via an electroless deposition process. This method provides the simplest scalable route yet to synthesize impermeable microcapsules with the added benefit that the final structure allows for drastically improving the overall volume of the encapsulated core to, in this case, >99% of the total volume. This method also allows for very good control over the microcapsule properties, and here we demonstrate our ability to tailor the final microcapsule density, capsule diameter, and secondary metal film thickness. Importantly, we also demonstrate that such impermeable microcapsule metal shells can be remotely fractured using ultrasound-based devices that are commensurate with technologies currently used in medical applications, which demonstrate the possibility to adapt these microcapsules for the delivery of cytotoxic drugs.

Optimizing the Preparation of Semi-Crystalline Paraffin/Poly(Urea-Formaldehyde) Microcapsules for Thermal Energy Storage

Paraffin, the most common phase change material, has been widely utilized as the core component in thermal energy storage in the form of microcapsules. In this study, semi-crystalline paraffin is capsulated into a poly(urea-formaldehyde) (PUF) shell by a two-step polymerization process. To obtain the microcapsule with good morphology and high latent heat, sodium chloride and crosslinker (a mixture of ammonium chloride and resorcinol with a weight ratio of 1:1) are incorporated and their addition amounts were optimized through differential scanning calorimetry (DSC) and SEM. The optimized microcapsules were obtained by adding 4 wt% sodium chloride, and 0.25 wt% crosslinker exhibits a diameter of several microns and a melting enthalpy of 110 J/g. This detailed study shows that sodium chloride strongly affects the morphology of paraffin emulsion by enlarging droplets, widening the size distribution, and enhancing the stability, which should be attributed to the enhancement of electric double layer strength. In addition, sodium chloride can weaken the Zeta potential of prepolymer and provides more opportunity for prepolymer to deposit on the surface of emulsion droplets. The two components in crosslinker play different roles in the polymerization process. Ammonium chloride reacts with prepolymers and reduces the pH of system, which can accelerate the curing process, while resorcinol probably participates in polymerization as a comonomer.

Size-controlled synthesis of polymer hollow nanoparticles using emulsion templates prepared by tandem acoustic emulsification

We have developed a new emulsion template method for the synthesis of poly(methylmethacrylate) (PMMA) hollow nanoparticles with different sizes. This synthetic method involves sequential ultrasonic irradiation (20 kHz → 500 kHz → 1.6 MHz → 2.4 MHz → 5.0 MHz) for acoustic emulsification of a water-insoluble fluorous solvent such as perfluoromethylcyclohexane (PFMCH) in an aqueous medium, followed by monomer (methylmethacrylate (MMA)) adsorption on the surface of the PFMCH emulsion droplets and photopolymerization of the adsorbed MMA in the obtained emulsion solution. Since the size of the PFMCH droplet templates can be tuned according to the number of steps of tandem acoustic emulsification, the obtained PMMA particle size can also be controlled. The subsequent removal of the core fluorous solvent by the heat treatment yielded size-controlled PMMA hollow nanoparticles and monodisperse PMMA hollow nanoparticles of different sizes. Furthermore, we confirmed that the substances could go in or go out of the hollow particles through the shells. Such a nice permeability is important for applications such as nanoreactors and drug delivery systems.

Influence of structural properties of emulsifiers on citral degradation in model emulsions.

The storage stability of compounds encapsulated in emulsions is strongly influenced by the properties of the droplet interfacial membrane. To evaluate the effect of emulsion droplet interface thickness on the degradation of citral, emulsions were prepared using polyoxyethylene alkyl ether-type emulsifiers with hydrophilic and hydrophobic groups of various sizes. Acid cyclization of citral at pH 3 promoted faster degradation than that at pH 7. Ferrous irons accelerated citral degradation in the emulsions at pH 3 but not at pH 7, because they decomposed the products of the acid-catalyzed cyclization of citral through redox reactions rather than direct degradation. Water-soluble radicals dramatically increased the rate of citral degradation, irrespective of pH. Notably, at low pH, the rate of citral degradation by ferrous irons was higher than that by radicals. These findings suggest that the thickness and density of emulsion droplet surfaces are not important factors for inhibiting citral degradation in emulsions.

Digestion fates of different edible oils vary with their composition specificities and interactions with bile salts

The digestion fates of different edible oils are different. The objective of this study was to understand the influences of lipid composition on their digestion fates, and investigate the roles of bile salts (BS) played in emulsified lipid system (whey protein isolate as emulsifier) in the in-vitro small intestine digestion stage. Three typical oils (palm oil (PO), rapeseed oil (RO) and linseed oil (LINO)) were chosen. Results showed that with the BS addition increased from 0.0 to 2.0 mg/mL, the increasing magnitude of the different fatty acid (FA) apparent release rate constants were: PO > RO ≈ LINO. Although the maximum FA release extent changed with BS addition, the order were: PO > RO > LINO. These may probably be attributed to palmitic acids, the most abundant FA in PO, was mostly located on the Sn-1, 3 positions of triacylglycerol (TAG) molecules, which contributed to the pancreatic lipase hydrolysis action. The relatively short chain length and the lower hydrophobicity also favored this process. However, Sn-1, 3 positions of TAGs in RO and LINO were mainly long chain mono- or poly-unsaturated FAs, which restricted the continuous lipid hydrolysis. Furthermore, the lipid composition may also affect the BS behavior on the O/W emulsion droplet surface, thus modulating lipase hydrolysis reaction. These findings can provide some basic understandings of the digestion differences of different oils.

Formulation and Characterization of a Pharmaceutical Pickering Emulsion

The ability of solid particles to adhere to soft deformable interfaces, for example to the surface of emulsion droplets or bubbles, is currently the subject of renewed interest in material science. On the other hand, Clay minerals are among the most widely used materials in pharmaceutical formulation, because of their properties as excipients and/or their biological activities. These features depend on both their colloidal dimensions and high surface. The phenomenon that solid particles can reside at the interface of droplets, thereby providing them with resistance against coalescence or Ostwald ripening, is known as Pickering stabilization. In this study Algerian bentonite clay is used for this purpose. An evaluation of the antibacterial activity of the emulsion after incorporation of the essential oil of Thymus fontanesii (local plant) also showed a fairly good encapsulation ability.

Chitosan-carboxymethylcellulose based microcapsules formulation for controlled release of active ingredients from cosmeto textile

Chitosan-based emulsions were prepared at pH from 4.0 to 6.0. The zeta potential and droplet size were monitored at different pH. Double emulsions (wateroil- water) were observed due to the stiff conformation of chitosan at pH 4.0. At pH 5.0, the emulsion droplets were the smallest (2.9 μm) of the experimental pH range. The emulsion droplets were well dispersed due to high surface charge of chitosan (for example, +50 mV at pH 5.5) in entire pH range. The emulsion was treated with carboxymethyl cellulose (CMC) for neutralizing the charged chitosan on the surface of emulsion droplets. Above 10×10−2 mg/ml of CMC, no change in zeta potential was observed indicating no more free chitosan existed after neutralization with CMC. The emulsion was then crosslinked with different amount of glutaraldehyde. Upon increasing the amount of glutaraldehyde, the amount of core content inside the microcapsule and encapsulation efficiency of shell materials decreased gradually. The Dynamic Scanning Calorimetry data confirmed no interaction between core and shell material in the microencapsulation process. The thermal degradation of the microcapsules was examined by thermogravimetric analysis and a gradual decrease in the degradation temperature upon increasing glutaraldehyde concentration was found. The tuning of CMC concentration can provide valuable information regarding stable emulsion and efficient microcapsule formulation via coacervation.

A study of the nature of plasma protein adsorption on the surface of perfluorocarbon emulsions stabilized by different triblock copolymers

The composition of plasma proteins adsorbed on the surface of perfluorocarbon emulsions stabilized by different triblock copolymers and their quantitative ratio were analyzed. The results allowed us to describe three types of protein adsorption on the surface of emulsion droplets. Opsonin proteins prevailed during the first type of adsorption. Their adsorption occurred on a dense and inactive layer of triblock copolymers. The second type of adsorption occurred due to the hydrophobic effect on a dense and mobile layer, with low-molecular-weight proteins being predominantly adsorbed (monoadsorption). The third type of adsorption occurred on a loose layer of triblock copolymers. In this case, the adsorption of a large amount of proteins with a molecular weight of 10–500 kDa was observed, while the total molecular weight was distributed over a large number of proteins.

Characterization of O/W Emulsions Prepared by PEG-Diisostearate Amphiphilic Random Copolymer.

We have characterized an emulsion system stabilized by an amphiphilic random copolymer, methoxy polyethylene glycol-23 methacrylate/glyceryl diisostearate methacrylate copolymer (MPM-GDM). The combined results of the static surface tension and transmission electron microscopy with freeze-fracture technique (FF-TEM) suggested that this copolymer forms aggregates in aqueous solutions. The membrane emulsification method produced an oil-in-water (O/W) emulsion in the mixture of squalane, water, and MPM-GDM, where the squalane concentration was set at 10 - 60 wt% and the MPM-GDM concentration was either 1 or 5 wt%. The prepared emulsion was stable against coalescence due to the formation of an adsorption layer of MPM-GDM. Based on the FF-TEM results, it is confirmed that a relatively large island-like structure is formed on the emulsion droplet surface. Furthermore, MPM-GDM can act as a thickening agent of the continuous liquid phase, which enhances the stability against creaming. The cooperative two effects improve the stability of the emulsion system without adding co-stabilizer such as low molecularweight surfactants.

Interfacial and emulsifying properties of crude and purified soybean oil bodies

Soybean oil bodies are natural and environment-friendly emulsifying agents from plant resources required as a substitute for emulsifiers such as low-molecular-weight one and animal proteins. The aim of this study was to reveal the interfacial properties and the emulsifying properties of two types of oil bodies extracted from soybean seeds at different pH conditions, that is purified oil bodies (OB) and crude oil bodies (OBC) including storage and other minor proteins. Particle size and zeta-potential measurements and SDS-PAGE revealed that the presence of the involved storage and other minor proteins promoted oil body aggregations and imparted the high zeta-potential to the oil bodies. OB adsorbed onto the oil-water (O/W) interface in closely packed state and formed more elastic adsorbed layer than OBC according to the results from tensiometry. Emulsions stabilized by OB (OB-E) were more stable against oil droplet coalescence than those by OBC (OBC-E) due to the absence of the involved proteins at the emulsion droplet surfaces. Cryo-SEM observation suggests that during emulsification most of the OB and OBC particles adsorbed onto the newly-created O/W interface and then rapidly ruptured.

Hierarchical CuO Colloidosomes and Their Structure Enhanced Photothermal Catalytic Activity

Hierarchical CuO colloidosomes (hollow spheres) constructed by subunit of open-mouthed hollow spheres that consist of 2D nanoleaves are synthesized via a Pickering emulsion strategy. Cu2O particles were served as emulsifier particles to form the Pickering emulsions. Self-oxidation of Cu2O gave rise to the formation of CuO nanoleaves which spontaneously cross-link the neighboring particles on the emulsion droplet surfaces, forming the robust colloidosomes. Concurrently, asymmetric Kirkendall effect produced the open-mouthed hollow structure in the subunit CuO particles, resulting in the hierarchical hollow structures of the colloidosomes. Because of the complex and multilevel hollow structure, the CuO colloidosomes significantly enhanced light harvest and photothermal conversion, leading to high local temperature (∼200 °C) on the surfaces under light irradiation at room temperature. This structure enhanced photothermal effect realized the photothermal catalytic CO oxidation at room temperature with a react...