Effect of molecular weight and degree of deacetylation of chitosan on the formation of oil-in-water emulsions stabilized by surfactant-chitosan membranes

The objective of this study was to establish the influence of polyelectrolyte characteristics (molecular weight and charge density) on the properties of oil-in-water emulsions containing oil droplets surrounded by surfactant-polyelectrolyte layers. A surfactant-stabilized emulsion containing small droplets (d32 approximately 0.3 microm) was prepared by homogenizing 20 wt% corn oil with 80 wt% emulsifier solution (20 mM SDS or 2.5 wt% Tween 20, 100 mM acetate buffer, pH 3) using a high-pressure valve homogenizer. This primary emulsion was then diluted with various chitosan solutions to produce secondary emulsions with a range of chitosan concentrations (3 wt% corn oil, 0-1 wt% chitosan). The influence of the molecular characteristics of chitosan on the properties of these emulsions was examined by using chitosan ingredients with different molecular weights (MW approximately 15, 145, and 200 kDa) and degree of deacetylation (DDA approximately 40, 77, and 92%). The electrical charge and particle size of the secondary emulsions were then measured. Extensive droplet aggregation occurred when the chitosan concentration was below the amount required to saturate the droplet surfaces, but stable emulsions could be formed at higher chitosan concentrations. The zeta-potential and mean diameter (d32) of the particles in the secondary emulsions was not strongly influenced by chitosan MW, however the chitosan with the lowest DDA (40%) produced droplets with smaller mean diameters and zeta-potentials than the other two DDA samples examined. Interestingly, we found that stable multilayer emulsions could be formed by mixing medium or high MW chitosan with an emulsion stabilized by a non-ionic surfactant (Tween 20) due to the fact the initial droplets had some negative charge. The information obtained from this study is useful for preparing emulsions stabilized by multilayer interfacial layers.     

Influence of environmental stresses on stability of oil-in-water emulsions containing droplets stabilized by beta-lactoglobulin-iota-carrageenan membranes

An oil-in-water emulsion (5 wt% corn oil, 0.5 wt% beta-lactoglobulin (beta-Lg), 0.1 wt% iota-carrageenan, 5 mM phosphate buffer, pH 6.0) containing anionic droplets stabilized by interfacial membranes comprising of beta-lactoglobulin and iota-carrageenan was produced using a two-stage process. A primary emulsion containing anionic beta-Lg coated droplets was prepared by homogenizing oil and emulsifier solution together using a high-pressure valve homogenizer. A secondary emulsion containing beta-Lg-iota-carrageenan coated droplets was formed by mixing the primary emulsion with an aqueous iota-carrageenan solution. The stability of primary and secondary emulsions to sodium chloride (0-500 mM), calcium chloride (0-12 mM), and thermal processing (30-90 degrees C) were analyzed using zeta-potential, particle size and creaming stability measurements. The secondary emulsion had better stability to droplet aggregation than the primary emulsion at NaCl 相似文献   

Production and characterization of oil-in-water emulsions containing droplets stabilized by multilayer membranes consisting of beta-lactoglobulin, iota-carrageenan and gelatin

The influence of environmental conditions (pH, NaCl, CaCl2, and temperature) on the properties and stability of oil-in-water (O/W) emulsions containing oil droplets surrounded by one-, two-, or three-layer interfacial membranes has been investigated. Three oil-in-water emulsions were prepared with the same droplet concentration and buffer (5 wt % corn oil, 5 mM phosphate buffer, pH 6) but with different biopolymers: (i) primary emulsion: 0.5 wt % beta-Lg; (ii) secondary emulsion: 0.5 wt % beta-Lg, 0.1 wt % iota-carrageenan; (iii) tertiary emulsion: 0.5 wt % beta-Lg, 0.1 wt % iota-carrageenan, 0-2 wt % gelatin. The secondary and tertiary emulsions were prepared by electrostatic deposition of the charged biopolymers onto the surfaces of the oil droplets so as to form two- and three-layer interfacial membranes, respectively. The stability of the emulsions to pH (3-8), sodium chloride (0-500 mM), calcium chloride (0-12 mM), and thermal processing (30-90 degrees C) was determined. We found that multilayer emulsions had better stability to droplet aggregation than single-layer emulsions under certain environmental conditions and that one or more of the biopolymer layers could be made to desorb from the droplet surfaces in response to specific environmental changes (e.g., high salt or high temperature). These results suggest that the interfacial engineering technology used in this study could lead to the creation of food emulsions with improved stability to environmental stresses or to emulsions with triggered release characteristics.     

Ethanol-in-oil emulsion (E/O) stabilized by polyglycerol polyricinoleate: A potential delivery system for ethanolic extract

This study evaluated how variations in polyglycerol polyricinoleate (PGPR) concentration and ethanol dispersed phase content affect the stability of ethanol-in-oil (E/O) emulsions. Results indicate that the stable 10?wt% E/O emulsions can be produced using 2?wt% PGPR. Increasing the ethanol dispersed phased content at constant PGPR concentration caused instability in emulsion. These emulsions remained stable to droplet flocculation and coalescence in the presence of Centella asiatica ethanol extract. PGPR does not greatly decrease the interfacial tension of the ethanol–oil interface. However, it adsorbed at the interface and stabilized the ethanol droplets in the emulsion via steric mechanism.     

Influence of Interfacial Engineering on Stability of Emulsions Stabilized with Soy Protein Isolate

The objectives of this study were to examine the influence interfacial composition on environmental stresses stability of oil in water emulsions. An electrostatic layer-by-layer deposition method was used to create the multilayered interfacial membranes with different compositions: (i) primary emulsion (Soy protein Isolate); (ii) secondary emulsion (Soy protein Isolate – OSA-starch); (iii) tertiary emulsion (Soy protein isolate – OSA-starch – chitosan). Fourier transform-infrared (FTIR) and scanning electron microscopy (SEM) results confirmed the adsorption of charged polyelectrolyte onto oppositely charge polyelectrolyte-coated oil droplets. The stability of primary, secondary, and tertiary emulsions to thermal treatment (30 min at 30–90°C), pH (3–7) and NaCl (0–500 mM) were determined using ζ-potential, particle diameter, and microstructure analysis. Primary emulsions were unstable at pH 4–7, salt concentrations, and thermal treatments. Secondary emulsions were stable to creaming and droplet aggregation at pH 3–5, at ≤50 mM NaCl, and unstable at thermal treatments, whereas tertiary emulsions were stable at all salt concentrations, thermal treatments, and at pH 3–6. These results demonstrate that these polymers can be used to engineer oil in water emulsion systems and improve the emulsion stability to environmental stresses.     

Fractional crystallization of oil droplets in O/W emulsions dispersed by Synperonic F127

The aim of this works is to study an oil-in-water emulsion stabilized with a triblock copolymer Synperonic F127 which presents a double size distribution of oil droplets. The emulsions were studied experimentally by means of differential scanning calorimetry (DSC) and dynamic light scattering (DLS). The DSC analysis was carried out focusing on the cooling behavior of the emulsion. The cooling thermograms of the oil-in-water emulsion revealed two crystallization peaks with Gaussian profile; the interesting characteristic is that both peaks are separated in temperature. In accordance to previous works for a single oil dispersed within an aqueous phase, the DSC technique must show a single Gaussian peak of crystallization attributable to a size distribution of droplets. In the present case of emulsions stabilized with 1 g/L of Synperonic F127, the aggregation behavior of triblock as a function of temperature allows to produce an emulsion with a double size droplet distribution. Comparison with emulsions stabilized with 2 and 4 wt% of non-ionic Tween 20 are also presented.     

Adsorption behaviour of lactoferrin in oil-in-water emulsions as influenced by interactions with beta-lactoglobulin

Oil-in-water emulsions (pH 7.0 or pH 3.0) containing 30 wt% soya oil and various concentrations of lactoferrin were made in a two-stage valve homogenizer. The average droplet size (d32), the surface protein coverage (mg/m2) and composition, and the zeta-potential of the emulsions were determined. The value of d32 decreased with increasing lactoferrin concentration up to 1%, and then was almost independent of lactoferrin concentration beyond 1% at both pH 7.0 and pH 3.0. The surface protein coverage of the emulsions made at pH 7.0 increased almost linearly with increasing lactoferrin concentration from 0.3 to 3%, but increased only slightly in emulsions made at pH 3.0 at lactoferrin concentrations >1%. The surface protein coverage of the emulsions made at pH 3.0 was lower than that of the emulsions made at pH 7.0 at a given protein concentration. The emulsion droplets had a strong positive charge at both pH 7.0 and pH 3.0, indicating that stable cationic emulsion droplets could be formed by lactoferrin alone. When emulsions were formed with a mixture of lactoferrin and beta-lactoglobulin (beta-lg) (1:1 by weight), the charge of the emulsion droplets was neutralized at pH 7.0 suggesting the formation of electrostatic complexes between the two proteins. The composition of the droplet surface layer showed that both proteins were adsorbed, presumably as complexes, from the aqueous phase at pH 7.0 in equal proportions, whereas competitive adsorption occurred between lactoferrin and beta-lg at pH 3.0. At this pH, beta-lg was adsorbed in preference to lactoferrin at low protein concentrations (1%), whereas lactoferrin appeared to be adsorbed in preference to beta-lg at high protein concentrations.     

Droplet surface properties and rheology of concentrated oil in water emulsions stabilized by heat-modified beta-lactoglobulin B

Effects of substituting native beta-lactoglobulin B (beta-lactoglobulin) with heat-treated beta-lactoglobulin as emulsifier in oil in water emulsions were investigated. The emulsions were prepared with a dispersed phase volume fraction of Phi=0.6, and accordingly, oil droplets rather closely packed. Native beta-lactoglobulin and beta-lactoglobulin heated at 69 degrees C for 30 and 45 min, respectively, in aqueous solution at pH 7.0 were compared. Molar mass determination of the species formed upon heating as well as measurements of surface hydrophobicity and adsorption to a planar air/water interface were made. The microstructure of the emulsions was characterized using confocal laser scanning microscopy, light scattering measurements of oil droplet sizes, and assessment of the amount of protein adsorbed to surfaces of oil droplets. Furthermore, oil droplet interactions in the emulsions were quantified rheologically by steady shear and small and large amplitude oscillatory shear measurements. Adsorption of heated and native beta-lactoglobulin to oil droplet surfaces was found to be rather similar while the rheological properties of the emulsions stabilized by heated beta-lactoglobulin and the emulsions stabilized by native beta-lactoglobulin were remarkably different. A 200-fold increase in the zero-shear viscosity and elastic modulus and a 10-fold increase in yield stress were observed when emulsions were stabilized by heat-modified beta-lactoglobulin instead of native beta-lactoglobulin. Aggregates with a radius of gyration in the range from 25 to 40 nm, formed by heating of beta-lactoglobulin, seem to increase oil droplet interactions. Small quantities of emulsifier substituted with aggregates have a major impact on the rheology of oil in water emulsions that consist of rather closely packed oil droplets.     

Influence of protein concentration and order of addition on thermal stability of beta-lactoglobulin stabilized n-hexadecane oil-in-water emulsions at neutral pH

The influence of protein concentration and order of addition relative to homogenization (before or after) on the extent of droplet flocculation in heat-treated oil-in-water emulsions stabilized by a globular protein were examined using laser diffraction. n-Hexadecane (10 wt%) oil-in-water emulsions (pH 7, 150 mM NaCl) stabilized by beta-lactoglobulin (beta-Lg) were prepared by three methods: (1) 4 mg/mL beta-Lg added before homogenization; (2) 4 mg/mL beta-Lg added before homogenization and 6 mg/mL beta-Lg added after homogenization; (3) 10 mg/mL beta-Lg added before homogenization. The emulsions were then subjected to various isothermal heat treatments (30-95 degrees C for 20 min), with the 150 mM NaCl being added either before or after heating. Emulsion 1 contained little nonadsorbed protein and exhibited extensive droplet aggregation at all temperatures, which was attributed to the fact that the droplets had a high surface hydrophobicity, e.g., due to exposed oil or extensive protein surface denaturation. Emulsions 2 and 3 contained a significant fraction of nonadsorbed beta-Lg. When the NaCl was added before heating, these emulsions were relatively stable to droplet flocculation below a critical holding temperature (75 and 60 degrees C, respectively) but showed extensive flocculation above this temperature. The stability at low temperatures was attributed to the droplets having a relatively low surface hydrophobicity, e.g., due to complete saturation of the droplet surface with protein or due to more limited surface denaturation. The instability at high temperatures was attributed to thermal denaturation of the adsorbed and nonadsorbed proteins leading to increased hydrophobic interactions between droplets. When the salt was added to Emulsions 2 and 3 after heating, little droplet flocculation was observed at high temperatures, which was attributed to the dominance of intra-membrane over inter-membrane protein-protein interactions. Our data suggests that protein concentration and order of addition have a strong influence on the flocculation stability of protein-stabilized emulsions, which has important implications for the formulation and production of many emulsion-based products.     

Influence of oil polarity on droplet growth in oil-in-water emulsions stabilized by a weakly adsorbing biopolymer or a nonionic surfactant

The influence of oil type (n-hexadecane, 1-decanol, n-decane), droplet composition (hexadecane:decanol), and emulsifier type (Tween 20, gum arabic) on droplet growth in oil-in-water emulsions was studied. Droplet size distributions of emulsions were measured over time (0-120 h) by laser diffraction and ultrasonic spectroscopy. Emulsions containing oil molecules of low polarity and low water solubility (hexadecane) were stable to droplet growth, irrespective of the emulsifier used to stabilize the droplets. Emulsions containing oil molecules of low polarity and relatively high water solubility (decane) were stable to coalescence, but unstable to Ostwald ripening, irrespective of emulsifier. Droplet growth in emulsions containing oil molecules of relatively high polarity and high water solubility (decanol) depended on emulsifier type. Decanol droplets stabilized by Tween 20 were stable to droplet growth in concentrated emulsions but unstable when the emulsions were diluted. Decanol droplets stabilized by gum arabic exhibited rapid and extensive droplet growth, probably due to a combination of Ostwald ripening and coalescence. We proposed that coalescence was caused by the relatively low interfacial tension at the decanol-water boundary, which meant that the gum arabic did not absorb strongly to the droplet surfaces and therefore did not prevent the droplets from coming into close proximity.     

Preparation characteristics of water-in-oil-in-water multiple emulsions using microchannel emulsification

Microchannel (MC) emulsification is a novel technique for preparing monodispersed emulsions. This study demonstrates preparing water-in-oil-in-water (W/O/W) emulsions using MC emulsification. The W/O/W emulsions were prepared by a two-step emulsification process employing MC emulsification as the second step. We investigated the behavior of internal water droplets penetrating the MCs. Using decane, ethyl oleate, and medium-chain triglyceride (MCT) as oil phases, we observed successful MC emulsification and prepared monodispersed oil droplets that contained small water droplets. MC emulsification was possible using triolein as the oil phase, but polydispersed oil droplets were formed from some of the channels. No leakage of the internal water phase was observed during the MC emulsification process. The internal water droplets penetrated the MC without disruption, even though the internal water droplets were larger than the resulting W/O/W emulsion droplets. The W/O/W emulsion entrapment yield was measured fluorometrically and found to be 91%. The mild action of droplet formation based on spontaneous transformation led to a high entrapment yield during MC emulsification.     

Influence of iota-carrageenan on droplet flocculation of beta-lactoglobulin-stabilized oil-in-water emulsions during thermal processing

The influence of thermal processing on droplet flocculation in oil-in-water emulsions stabilized by either beta-lactoglobulin (primary emulsions) or beta-lactoglobulin-iota-carrageenan (secondary emulsions) at pH 6 has been investigated. In the absence of salt, the zeta-potential of the primary emulsion was less negative (-40 mV) than that of the secondary emulsion (-55 mV) due to adsorption of anionic iota-carrageenan to the anionic beta-Lg-coated droplet surfaces. The zeta-potential and mean diameter (d(43) approximately 0.3 microm) of droplets in primary and secondary emulsions did not change after storage at temperatures ranging from 30 to 90 degrees C. In the presence of 150 mM NaCl, the zeta-potential of the primary emulsion was much less negative (-27 mV) than that of the secondary emulsion (-50 mV), suggesting that the latter was less influenced by electrostatic screening effects. The zeta-potential of the primary emulsions did not change after storage at elevated temperatures (30-90 degrees C). The zeta-potential of the secondary emulsions became less negative, and the aqueous phase iota-carrageenan concentration increased at storage temperatures exceeding 50 degrees C, indicating iota-carrageenan desorbed from the beta-Lg-coated droplets. In the primary emulsions, appreciable droplet flocculation (d(43) approximately 8 microm) occurred at temperatures below the thermal denaturation temperature (T(m)) of the adsorbed proteins due to surface denaturation, while more extensive flocculation (d(43) > 20 microm) occurred above T(m) due to thermal denaturation. In the secondary emulsions, the extent of droplet flocculation below T(m) was reduced substantially (d(43) approximately 0.8 microm), which was attributed to the ability of adsorbed carrageenan to increase droplet-droplet repulsion. However, extensive droplet flocculation was observed above T(m) because carrageenan desorbed from the droplet surfaces. Differential scanning calorimetry showed that iota-carrageenan and beta-Lg interacted strongly in aqueous solutions containing 0 mM NaCl, but not in those containing 150 mM NaCl, presumably because salt weakened the electrostatic attraction between the molecules.     

New Pickering emulsions stabilized by bacterial cellulose nanocrystals

We studied oil in water Pickering emulsions stabilized by cellulose nanocrystals obtained by hydrochloric acid hydrolysis of bacterial cellulose. The resulting solid particles, called bacterial cellulose nanocrystals (BCNs), present an elongated shape and low surface charge density, forming a colloidal suspension in water. The BCNs produced proved to stabilize the hexadecane/water interface, promoting monodispersed oil in water droplets around 4 μm in diameter stable for several months. We characterized the emulsion and visualized the particles at the surface of the droplets by scanning electron microscopy (SEM) and calculated the droplet coverage by varying the BCN concentration in the aqueous phase. A 60% coverage limit has been defined, above which very stable, deformable droplets are obtained. The high stability of the more covered droplets was attributed to the particle irreversible adsorption associated with the formation of a 2D network. Due to the sustainability and low environmental impact of cellulose, the BCN based emulsions open opportunities for the development of environmentally friendly new materials.     

Effects of electrolyte concentration and pH on the coalescence stability of beta-lactoglobulin emulsions: experiment and interpretation

Experimental results are presented about the effects of ionic strength and pH on the mean drop-size after emulsification and on the coalescence stability of emulsions, stabilized by a globular protein beta-lactoglobulin (BLG). The mean drop-size is determined by optical microscopy, whereas the coalescence stability is characterized by centrifugation. In parallel experiments, the zeta-potential and protein adsorption on drop surface are determined. The experiments are performed at two different BLG concentrations, 0.02 and 0.1 wt%. The electrolyte concentration in the aqueous phase, C(EL), is varied between 1.5 mM and 1 M, and pH is varied between 4.0 and 7.0. The experiments show that the mean drop-size after emulsification depends slightly on C(EL), at fixed protein concentration and natural pH = 6.2. When pH is varied, the mean drop-size passes through a maximum at fixed protein and electrolyte concentrations. A monolayer protein adsorption is registered in the studied ranges of C(EL) and pH at low BLG concentration of 0.02 wt%. In contrast, a protein multilayer is formed at higher BLG concentration, 0.1 wt%, above a certain electrolyte concentration (C(EL) > 100 mM, natural pH). The experimental results for the emulsion coalescence stability are analyzed by considering the surface forces acting between the emulsion drops. The electrostatic, van der Waals, and steric interactions are taken into account to calculate the barriers in the disjoining pressure isotherm at the various experimental conditions studied. The comparison of the theoretically calculated and the experimentally determined coalescence barriers shows that three qualitatively different cases can be distinguished. (1) Electrostatically stabilized emulsions, with monolayer protein adsorption, whose stability can be described by the DLVO theory. (2) Sterically stabilized emulsions, in which the drop-drop repulsion is created mainly by overlapping protein adsorption multilayers. A simple theoretical model is shown to describe emulsion stability in these systems. (3) Sterically stabilized emulsions with a monolayer adsorption on drop surface.     

Double inversion of emulsions induced by salt concentration

The effects of salt on emulsions containing sorbitan oleate (Span 80) and Laponite particles were investigated. Surprisingly, a novel double phase inversion was induced by simply changing the salt concentration. At fixed concentration of Laponite particles in the aqueous phase and surfactant in paraffin oil, emulsions are oil in water (o/w) when the concentration of NaCl is lower than 5 mM. Emulsions of water in oil (w/o) are obtained when the NaCl concentration is between 5 and 20 mM. Then the emulsions invert to o/w when the salt concentration is higher than 50 mM. In this process, different emulsifiers dominate the composition of the interfacial layer, and the emulsion type is correspondingly controlled. When the salt concentration is low in the aqueous dispersion of Laponite, the particles are discrete and can move to the interface freely. Therefore, the emulsions are stabilized by particles and surfactant, and the type is o/w as particles are in domination. At intermediate salt concentrations, the aqueous dispersions of Laponite are gel-like, the viscosity is high, and the transition of the particles from the aqueous phase to the interface is inhibited. The emulsions are stabilized mainly by lipophilic surfactant, and w/o emulsions are obtained. For high salt concentration, flocculation occurs and the viscosity of the dispersion is reduced; thus, the adsorption of particles is promoted and the type of emulsions inverts to o/w. Laser-induced fluorescent confocal micrographs and cryo transmission electron microscopy clearly confirm the adsorption of Laponite particles on the surface of o/w emulsion droplets, whereas the accumulation of particles at the w/o emulsion droplet surfaces was not observed. This mechanism is also supported by the results of rheology and interfacial tension measurements.     

Influence of pH on the stability of oil-in-water emulsions stabilized by a splittable surfactant

A laboratory study was conducted to evaluate the effect of pH on the stability of oil-in-water emulsions stabilized by a commercial splittable surfactant Triton SP-190 by comparison with the results obtained by a common surfactant Triton X-100. The emulsion stability was explored by measuring the volume of oil phase separated and the size of the dispersed droplets. It was found that the addition of inorganic acids did not significantly affect the stability of emulsions stabilized by Triton X-100, but had a profound influence on the stability of emulsions stabilized by Triton SP-190. Moreover, the droplet size of a Triton X-100-stabilized emulsion and its dynamic interfacial activity were insensitive to acids. However, at lower pH the droplet size of the emulsions stabilized by Triton SP-190 was considerably increased. From the dynamic interfacial tension measurements the dynamic interfacial activity of Triton SP-190 at the oil/water interface was found to be strongly inhibited by the addition of acids, resulting in a slower decreasing rate of dynamic interfacial tension. The results demonstrate that the dramatic destabilization of Triton SP-190-stabilized emulsions could be realized by the use of acids, which evidently changed the interfacial properties of the surfactant and resulted in a higher coalescence rate of oil droplets.     

Simple, reversible emulsion system switched by pH on the basis of chitosan without any hydrophobic modification

Chitosan without hydrophobic modification is not a good emulsifier itself. However, it has a pH-tunable sol-gel transition due to free amino groups along its backbone. In the present work, a simple reversible Pickering emulsion system based on the pH-tunable sol-gel transition of chitosan was developed. At pH > 6.0, as adjusted by NaOH, chitosan was insoluble in water. Chitosan nanoparticles or micrometer-sized floccular precipitates were formed in situ. These chitosan aggregates could adsorb at the interface of oil and water to stabilize the o/w emulsions, so-called Pickering emulsions. At pH < 6.0, as adjusted by HCl, chitosan was soluble in water. Demulsification happened. Four organic solvents (liquid paraffin, n-hexane, toluene, and dichloromethane) were chosen as the oil phase. Reversible emulsions were formed for all four oils. Chitosan-based Pickering emulsions could undergo five cycles of emulsification-demulsification with only a slight increase in the emulsion droplet size. They also had good long-term stability for more than 2 months. Herein, we give an example of chitosan without any hydrophobic modification to act as an effective emulsifier for various oil-water systems. From the results, we have determined that natural polymers with a stimulus-responsive sol-gel transition should be a good particulate emulsifier. The method for in situ formation of pH-responsive Pickering emulsions based on chitosan will open up a new route to the preparation of a wide range of reversible emulsions.     

Particle self-assembly in oil-in-ionic liquid Pickering emulsions

We have studied polydimethylsiloxane (PDMS)-in-1-butyl-3-methylimidazolium hexafluorophosphate ([BMIM][PF(6)]) Pickering emulsions stabilized by polystyrene microparticles with different surface chemistry. Surprisingly, in contrast to the consensus originating from oil/water Pickering emulsions in which the solid particles equilibrate at the oil-water droplet interfaces and provide effective stabilization, here the polystyrene microparticles treated with sulfate, aldehyde sulfate, or carboxylate dissociable groups mostly formed monolayer bridges among the oil droplets rather than residing at the oil-ionic liquid interfaces. The bridge formation inhibited individual droplet-droplet coalescence; however, due to low density and large volume (thus the buoyant effect), the aggregated oil droplets actually promoted oil/ionic liquid phase separation and distressed emulsion stability. Systems with binary heterogeneous polystyrene microparticles exhibited similar, even enhanced (in terms of surface chemistry dependence), bridging phenomenon in the PDMS-in-[BMIM][PF(6)] Pickering emulsions.     

Optimizing organoclay stabilized Pickering emulsions

Oil-in-water emulsions were prepared using montmorillonite clay platelets, pre-treated with quaternary amine surfactants. In previous work, cetyl trimethylammonium bromide (CTAB) has been used. In this study, two more hydrophilic quaternary amine surfactants, Berol R648 and Ethoquad C/12, were used and formed Pickering emulsions, which were more stable than the emulsions prepared using CTAB coated clay. The droplets were also more mono-disperse. The most hydrophilic surfactant Berol R648 stabilizes the emulsions best. Salt also plays an important role in forming a stable emulsion. The droplet size decreases with surfactant concentration and relatively mono-disperse droplets can be obtained at moderate surfactant concentrations. The time evolution of the droplet size indicates a good stability to coalescence in the presence of Berol R648. Using polarizing microscopy, the clay platelets were found to be lying flat at the water oil interface. However, a significant fraction (about 90%) of clay stayed in the water phase and the clay particles at the water-oil interface formed stacks, each consisting of four clay platelets on average.     

Emulsifying potency of new amino acid-type surfactant (II): stable water-in-oil (W/O) emulsions containing 85 wt% inner water phase

The ternary phase diagram for N-[3-lauryloxy-2-hydroxypropyl]-L-arginine L-glutamate (C12HEA-Glu), a new amino acid-type surfactant, /oleic acid (OA)/water system was established. The liquid crystal and gel complex formations between C12HEA-Glu and OA were applied to a preparation of water-in-oil (W/O) emulsions. Stable W/O emulsions containing liquid paraffin (LP) as the oil and a mixture of C12HEA-Glu and OA as the emulsifier were formed. The preparation of stable W/O emulsions containing 85 wt% water phase was also possible, in which water droplets would be polygonally transformed and closely packed, since the maximum percentage of inner phase is 74% assuming uniformly spherical droplets. Water droplets would be taken into the liquid crystalline phase (or the gel complex) and the immovable water droplets would stabilize the W/O emulsion system. The viscosity of emulsions abruptly increased above the 75 wt% water phase (dispersed phase). The stability of W/O emulsions with a lower weight ratio of OA to C12HEA-Glu and a higher ratio of water phase was greater. This unusual phenomenon may be related to the formation of a liquid crystalline phase between C12HEA-Glu and OA, and the stability of the liquid crystal at a lower ratio of oil (continuous phase). W/O and oil-in-water (O/W) emulsions containing LP were selectively prepared using a mixture of C12HEA-Glu and OA since the desirable hydrophile-lipophile balance (HLB) number for the emulsification was obtainable by mixing the two emulsifiers.