Fat Crystals Influence Methylcellulose Stabilization of Lipid Emulsions

Oil-in-water emulsions stabilized with methylcellulose (MC) varied in stability depending on the composition of the fat phase. When droplets were composed entirely of liquid oil, MC was able to form a continuous, protective film around the droplets. Therefore, when two liquid oil droplets were brought into contact, they underwent extreme shape deformation but did not coalesce, even when excess force was used. Subsequently, interfacial crystals extending into the aqueous phase from palm kernel oil droplets were aimed into an entirely liquid oil droplet. The MC-coated droplet would deform wherever the crystal contacted; however, the protruding crystals could not penetrate into the liquid oil droplet. Conversely, when the target droplet was composed of a small amount of solid fat that resulted in localized crystalline regions and the interfacial crystals of the second droplet were aimed at this region, they then easily pierced the droplet. This demonstrates that MC is an excellent stabilizer for liquid oil droplets but internal lipid crystals within fat globules can alter MC surface conformation to allow for crystal penetration and arrested coalescence.     

Continuous-phase fat crystals strongly influence water-in-oil emulsion stability

To elucidate the role of continuous-phase fat crystals on emulsion destabilization, water-in-canola oil emulsions prepared with 0–2% (w/w) added solid fat (hydrogenated canola stearine or hydrogenated cottonseed stearine) were examined using pulsed NMR droplet-size analysis, sedimentation, and microscopy. Droplet-size analysis showed that addition of either fat prior to emulsification (precrystallized fat) or fat quench-crystallized in situ following emulsification (postcrystallized fat) decreased the degree of droplet coalescence, based on volume-weighted (d ₃₃) mean droplet diameters, with postcrystallized emulsions being more stable against coalescence. Sedimentation studies corroborated these results, with greatly enhanced stability against sedimentation in postcrystallized emulsions. Precrystallized fat had very little effect on emulsion sedimentation at levels as high as 2% (w/w). Postcrystallized cottonseed stearine produced slightly less resistant emulsions than did canola stearine, even if both were in the β-form. Surface energetics revealed that canola stearine had greater affinity for the oil/water interface and hence a greater displacement energy. The presence of micronsized (Pickering) crystals located directly at the droplet interface, resulting from in situ crystallization or generated by the shearing of precrystallized fats, provided enhanced stability vis-à-vis preformed crystals. These stabilized emulsions via the formation of crystal networks that partially immobilized droplets.     

Effect of lipid type on water‐in‐oil‐emulsions stabilized by phosphatidylcholine‐depleted lecithin and polyglycerol polyricinoleate

Water‐in‐oil (W/O, 30:70) emulsions were prepared with phosphatidylcholine‐depleted lecithin [PC/(PI,PE) = 0.16] or polyglycerol polyricinoleate (PGPR) as emulsifying agents by means of pressure homogenization. The effect of lipid type (medium‐chain triacylglycerols, sunflower, olive, butter oil, or MCT‐oil/vegetable fat blends) was investigated in relation to particle size distribution, coalescence stability and the sedimentation of the water droplets. A significant correlation (p <0.05) was observed between the interfacial pressure caused by the addition of lecithin to the pure lipids and the specific surface area of the emulsion droplets (r_s = 0.700), and between the viscosity of the lipids used as the continuous phase (reflecting the fatty acid composition) and the specific surface area of the emulsion droplets (r_s = 0.8459) on the other hand. Blends of vegetable fat and MCT‐oil led to reduced coalescence stability due to the attachment of fat crystals to the emulsion droplets. Lecithin‐stabilized W/O emulsions showed significantly higher viscosities compared to those stabilized with PGPR. It was possible to adjust the rheological properties of lecithin‐stabilized emulsions by varying the lipid phase.     

Stabilization of water-in-oil emulsions by submicrocrystalline α-form fat particles

The results presented in this study confirm previous knowledge and stress the need for both hydrophobic emulsifiers and submicronial fat particles to stabilize water-in-vegetable oil emulsions. It was demonstrated that polyglycerol polyricinoleate (PGPR) is superior to glycerol monooleate and/or lecithin, but is incapable of stabilizing these fluid emulsions for sufficient storage periods. Fluid emulsions, unlike margarine, exhibit high droplet mobility and are susceptible to flocculation and coalescence. It was also demonstrated that submicronial α-form crystals of hydrogenated fat can be obtained in the oil phase by the flash-cooling process. The crystals are homogeneously almost mono-dispersed and exhibit insufficient stability against flocculation and phase separation. The use of an emulsifier (PGPR) in the fat crystallization process was very helpful in decreasing the aggregation and flocculation processes. The α-form (mixed with β′-form) submicronial crystals can stabilize water-in-oil emulsions only in the presence of food emulsifiers, provided the concentration of tristearin is limited to 1.0–2.0 wt% (to prevent phase separation and high viscosity) and the PGPR is added at sufficient concentrations (PGPR/tristearin ratio of 2.0 or more). Ideally stable (for over 6–8 wk) fluid emulsions can be formed in systems composed of fat submicrocrystalline hydrophilic particles and food-grade emulsifiers. These water-in-oil emulsions can serve as the basic preparation for any food-grade water-in-oil-in-water double emulsion.     

Interfacial Crystallization of Diacylglycerols Rich in Medium‐ and Long‐Chain Fatty Acids in Water‐in‐Oil Emulsions

The effects of diacylglycerols rich in medium‐ and long‐chain fatty acids (MLCD) on the crystallization of hydrogenated palm oil (HPO) and formation of 10% water‐in‐oil (W/O) emulsion are studied, and compared with the common surfactants monostearoylglycerol (MSG) and polyglycerol polyricinoleate (PGPR). Polarized light microscopy reveals that emulsions made with MLCD form crystals around dispersed water droplets and promotes HPO crystallization at the oil‐water interface. Similar behavior is also observed in MSG‐stabilized emulsions, but is absent from emulsions made with PGPR. The large deformation yield value of the test W/O emulsion is increased four‐fold versus those stabilized via PGPR due to interfacial crystallization of HPO. However, there are no large differences in droplet size, solid fat content (SFC), thermal behavior or polymorphism to account for these substantial changes, implying that the spatial distribution of the HPO crystals within the crystal network is the driving factor responsible for the observed textural differences. MLCD‐covered water droplets act as active fillers and interact with surrounding fat crystals to enhance the rigidity of emulsion. This study provides new insights regarding the use of MLCD in W/O emulsions as template for interfacial crystallization and the possibility of tailoring their large deformation behavior. Practical Applications: MLCD is applied in preparing W/O emulsion. It is found that MLCD forms unique interfacial Pickering crystals around water droplets, which promote the surface‐inactive HPO nucleation at the oil‐water interface. Thus MLCD‐covered water droplets act as active fillers and interact with surrounding fat crystals, which can greatly enhance the rigidity of emulsion. This observation would provide a theoretical reference and practical basis for the application of the MLCD with appreciable nutritional properties in lipid‐rich products such as whipped cream, shortenings margarine, butter and ice cream, so as to substitute hydrogenated oil. MLCD‐stabilized emulsions can also be explored for the development of novel confectionery products, lipsticks, or controlled release matrices.     

Experimental characterization of emulsion formation and coalescence by nuclear magnetic resonance restricted diffusion techniques

Nuclear magnetic resonance (NMR) is explored as a technique for noninvasively monitoring emulsion droplet formation and destabilization. The method makes use of the fact that the diffusion of oil molecules within oil-in-water emulsion droplets results in attenuation of a coherent magnetic signal that emanates from those molecules. If oil diffusion is limited by the size of the droplet, the shape of a plot of attenuation over time is directly affected by the droplet radius. We use this approach to determine noninvasively the effect of surfactant type, surfactant concentration, pH, and ionic strength on droplet sizes within a 40 wt% octane and water emulsion, stabilized by Tween 20 or β-lactoglobulin (β-Lg). We find that addition of the low-molecular-weight Tween 20 forms finer emulsion droplets than does addition of the protein, and that the Tween 20 emulsion is sensitive to surfactant concentration below a threshold “saturation” concentration. The droplet sizes in β-Lg-containing emulsions increase as pH increases above the isoelectric point and as ionic strength increases. The fact that the NMR technique does not mistake clusters of droplets for single large droplets makes the analysis of these effects unambiguous. We further extend the use of NMR diffusion techniques to monitor the effect of surfactant type, surfactant concentration, and convection on the rate of droplet coalescence. The ability of NMR methods to distinguish between large single droplets and droplet clusters makes it well-suited to monitor coalescence processes independently from flocculation.     

Double emulsions of water-in-oil-in-water stabilized by α-form fat microcrystals. Part 1: Selection of emulsifiers and fat microcrystalline particles

Double emulsions are commonly stabilized by monomeric and/or polymeric emulsifiers. Pickering stabilization by solid particles such as colloidal microcrystalline cellulose has been mentioned only once as a possible technique to stabilize the external interface of the water-in-oil-in-water emulsion. No further work was carried out exploring this option. The present study shows that solid microcrystalline fat particles of α-form are capable of adsorbing at the water-oil interface and, together with other hydrophobic emulsifiers, can stabilize water-in-oil (W/O) emulsions. The crystals must be submicron in size in order to effectively adsorb and arrange at the interface. Large crystals do not fit and were found to flocculate as free crystals in the continuous oil phase. The α-form crystals can be obtained by flash-cooling saturated triglycerides in vegetable oils in the presence of emulsifiers, such as polyglycerol polyricinoleate (PGPR), that stabilize the dispersion and serve as α-tending crystal structure modifiers. It was assumed that PGPR also serves as a cross-linker or bridge between the crystalline fat particles and the water, and facilitates the anchoring of the fat particles in the oil phase in one direction while dangling itself in the water phase. The double emulsion droplets prepared with these W/O emulsions are relatively large in size (6–18 μm), but stable to coalescence. The marker (NaCl) does not seem to release with time, suggesting that the fat particles form microcapsules on the water interface, totally sealing the water from releasing its addenda. The systems seem to have a significant potential for food emulsions.     

Effectiveness of Polyoxyethylene Nonionic Emulsifiers in Emulsification Processes Using Disc Systems

Additives such as emulsifiers and stabilizers (viscosity enhancers or polymers) are needed to stabilize emulsion systems against coalescence and creaming. A way to reduce emulsifier input by determining the effectiveness of different emulsifiers is described. Only disc systems with optimized configuration are applied for emulsification. Polysorbates are taken as an example for emulsifiers. The viscosity was increased with pectin as a viscosity enhancer to allow higher energy inputs by the disc systems and, therefore, to improve droplet disruption. The attainable mean diameters of oil droplets stabilized only by pectin were compared with the resulting mean diameters of oil droplets of emulsions containing polysorbates. Polysorbate 20, the emulsifier with the highest water solubility of all here described emulsifiers, proved to be the most effective in decreasing the mean diameter of the disperse phase when using disc systems. An optimal emulsifier concentration of 2 wt‐% for emulsions at low viscosities is observed for all polysorbates and for the whole range of oil concentration.     

Edible oil-in-water emulsions stabilized by hydrophile–lipophile balanced sucrose ester

Conventional emulsions are mostly stabilized by surfactants and for stabilization of oil-in-water emulsions the surfactants should be hydrophilic or with HLB numbers larger than seven. In this work, we report that edible oil-in-water emulsions can also be stabilized by surfactants with an HLB value close to seven. With edible sucrose ester C-1807 (HLB no. = 7) as emulsifier and three edible oils (canola oil, olive oil, soybean oil), edible oil-in-water emulsions can be stabilized by C-1807 at concentrations beyond its critical aggregation concentration (CAC). Although monomeric C-1807 behaves as an inferior emulsifier, they assemble to form multilamellar vesicles in water at concentrations higher than the CAC giving a viscoelastic/gel-like aqueous phase which is partly responsible for emulsion stabilization. Specifically, at 2 wt%, high internal phase emulsions (HIPEs) with ϕ_o = 0.75 can be obtained, which are stable against cooling–heating cycles between 5 and 30°C during storage. The vesicles disperse in the aqueous lamellae surrounding the oil droplets, which together with the viscoelastic/gel-like continuous phase prevents them from flocculation and coalescence.     

Coalescence dynamics of two droplets of different viscosities in T-junction microchannel with a funnel-typed expansion chamber

The coalescence behavior of two droplets with different viscosities in the funnel-typed expansion cham-ber in T-junction microchannel was investigated experimentally and compared with droplet coalescence of the same viscosity.Four types of coalescence regimes were observed:contact non-coalescence,squeeze non-coalescence,two-droplet coalescence and pinch-off coalescence.For droplet coalescence of different viscosities,the operating range of non-coalescence becomes narrowed compared to the droplet coalescence of same viscosity,and it shrinks with increasing viscosity ratio η of two droplets,indicating that the difference in the viscosity of two droplets is conducive to coalescence,especially when 1 ＜ η＜ 6.Furthermore,the influences of viscosity ratio and droplet size on the film drainage time (Tdr) and critical capillary number (Cac) were studied systematically.It was found that the film drainage time declined with the increase of average droplet size,which abided by power-law relation with the size dif-ference and viscosity ratio of the two droplets:Tdr ～ (ld)0.25±0.04 and Tdr ～ (η)-0.1±002.For droplet coales-cence of same viscosity,the relation of critical capillary number with two-phase viscosity ratio and dimensionless droplet size is Cac =0.48λ0.26l-2.64,while for droplet coalescence of different viscosities,the scaling of critical capillary number with dimensionless average droplet size,dimensionless droplet size difference and viscosity ratio of two droplets is Cac =0.11 η-0.07ls-2.23ld0.16.     

Drop mixing in suspension polymerisation

In suspension polymerisation, monomer is suspended as liquid droplets in a continuous water phase by means of strong agitation and the presence of a suspending agent. As the suspension polymerisation proceeds, the viscosity of a monomer-polymer droplet increases with conversion. Hence, the physical behaviour of the droplet changes during the process. When new dispersible material is added to the existing suspension drops, the new material and existing drops can remain segregated for significant amounts of time. The aim of this project was to study the behaviour of drop mixing when new material is added to the existing suspension polymerisation. This study concentrated on the effect of the dispersed phase viscosity on drop mixing. The results show that viscosity affects drop size and that may then affect the rate of coalescence between drops. A critical drop size exists which determines the coalescence efficiency effect. Above the critical drop size, mixing rate increases as the drop viscosity decreases. While below the critical drop size, drop size of the dispersion determines the coalescence rate; as the drop size increases, coalescence rate also increases. The investigation of the effect of suspending agent shows that Tween 20 is more efficient in stabilising and protecting the drops, based on a weight basis, than PVA as the coalescence rate is lower with Tween 20.     

Thermal behavior of fat droplets as related to adsorbed milk proteins in complex food emulsions. A DSC study

The thermal behavior of hydrogenated palm kernel oil-in-water emulsions, which differed in their milk-protein composition, was studied in parallel with other characteristic parameters such as the aggregation/coalescence of fat droplets, and the proportion of adsorbed proteins at the oil/water interface. DSC was applied to monitor the crystallization and melting behavior of nonemulsified and emulsified fat samples. Comparison between nonemulsified and emulsified fat samples showed that in emulsified samples the initial temperature of fat crystallization and the temperature of the completion of melting were invariably lower and slightly higher, respectively. Furthermore, in complex food emulsions the supercooling temperature needed to initiate fat crystallization and the variation in its growth rate in the cooling experiment were dependent on the amount and nature of the adsorbed proteins. Our results indicate that the total replacement of milk proteins by whey proteins affected the fat crystallization behavior of emulsified fat droplets, in parallel with changes in their protein surface coverage and in their physical stability against fat droplet agglomeration.     

De-emulsification of 2-ethyl-1-hexanol/water emulsion using oil-wet narrow channel combined with low-speed rotation

Low-speed rotation of disc in an internal circulation of a novel de-emulsification with rotation-dise horizental contactor (RHC-D) realized de-emulsification for O/W emulsions due to repeated coalescence in oil-wet narrow channels at a low rotation speed. For three emulsions included ethanol/water/2-ethyl-1-hexanol, ethanol/water/2-ethyl-1-hexanol/SDS (Sodium Dodecyl Sulfonate) and 2-ethyl-1-hexanol/water/SDS emulsion, deemulsification ratios of oil phase could reach 1, 1 and 0.67 respectively at 170 r·min^-1, and de-emulsification ratios increased obviously after agitating 10 min. De-emulsification experiment in the seam indicated that oil droplet sizes in O/W emulsion became larger after de-emulsification. The main de-emulsification mechanism in RHCD was the coalescence of oil droplets in oil-wet narrow channels. With increase of the rotation speed, oil droplets dispersed better in the aqueous phase. However, de-emulsification effect enhanced due to the increase of the coalescence rate at a bit higher rotation speed. In addition, internal circulation made those O/W emulsions to be broken repeatedly, consequently de-emulsification ratio increased. Repeated de-emulsification through internal circulation might make continuous extraction of ethanol come true at a low rotation speed.     

Interfacial phenomena and droplet size of particle stabilized emulsions in oscillatory shear

Production of particle stabilized oil in water emulsions has been investigated both theoretically and experimentally under oscillatory shear conditions using different stabilizing particles (SPs). The investigation included analysis of the interaction between particles interfacial stability and droplets breakage and coalescence. For hydrophobic SPs, droplets maintained their sizes as determined by torque balance (TB) without significant breakage or coalescence. For the more hydrophilic SPs, larger droplets formed that broke by eddies in the inertial subrange. At higher fluid shear stresses, loss of the SPs occurred during droplet formation leading to near bare droplet surface and coalescence to much larger sizes with subsequent fragmentation by capillary instabilities. The final droplet size in both cases was very different from TB model predictions. A modeling approach is proposed that combined both TB and droplet breakage and coalescence mechanisms. Comparison between the experimental results and the models predictions showed satisfactory agreement. © 2016 American Institute of Chemical Engineers AIChE J, 62: 2902–2911, 2016     

Coalescence of Water-in-Shale Oil Emulsions

Abstract

The coalescence and interfacial behavior of water-in-shale oil emulsions in the presence of chemical additives was studied using photomicrographic analysis. Both the coalescence and flocculation rate constants were determined as a function of the demulsifier concentration. The coalescence rates increased and the interfacial viscosity decreased with an increase in the temperature. These changes are due to the decrease in bulk and interfacial viscosities with increase in temperature, higher temperatures facilitating better film drainage and hence better coalescence rates. The overall coalescence rate goes through a maximum as the speed of agitation is increased. This maximum may be explained by the mechanism of flocculation and redispersion. The presence of solids was seen to significantly increase the stability of these emulsions.     

Erdöl-Emulsionen — Eigenschaften,Stabilität und Spaltung

Petroleum emulsions — Properties, stability, and demulsification . Petroleum always occurs together with brine and is often recovered as an water-in-oil emulsion. Emulsions containing more than 90 percent of water are known; they are often very stable. The viscosity of the emulsions rises at a faster rate than the water content and is always significantly higher than that calculated according to the Einstein equation. Petroleum emulsions are stabilized by adsorption of the asphaltenes and petroleum resins colloidally dispersed in the petroleum. These components form mechanically stable films at the water/oil interface. The films contain several anionic, cationic, and amphoteric interfacially active substances, which are associated to form micelles, and which are adsorbed at the oil/water interface as a result of their interfacial activity. The adsorption films are wetted by the oil phase. The emulsions are stable towards coalescence, but not towards flocculation. Demulsifying agents displace the stabilizers from the interface or change their wettability.     

驱油剂对三元复合驱含油污水中油滴稳定性的影响

三元复合驱技术已在大庆油田成功进行工业化应用。三元复合驱含油污水中由于含有残余的化学药剂，导致其很难处理，从而限制了三元复合驱技术的推广。本文首先采用室内实验制备模拟三元复合驱含油污水，然后通过沉降实验研究驱油剂对油滴稳定性的影响，最后结合驱油剂对油水界面张力、油滴Zeta电位、油滴粒径大小的影响来阐释驱油剂对油滴稳定性的作用机制。结果表明：油滴的稳定性随着NaOH浓度的增大先增大后减小，当NaOH浓度由0增大到400mg/L时，NaOH与原油中的酸性物质反应生成表面活性剂增强油滴的稳定性；当NaOH浓度大于400mg/L时，NaOH本身作为电解质压缩双电层，使油滴的稳定性减小。油滴的稳定性随着表面活性剂浓度的增大而增大，这是因为表面活性剂可以吸附在油滴表面，使油水界面张力减小，同时增大油滴表面的Zeta电位，从而使油滴的稳定性增强。油滴的稳定性随着聚合物浓度的增大先减小后增大，当聚合物的浓度小于300mg/L时，聚合物的桥接、絮凝作用起主导作用，聚合物分子可以吸附到油滴表面，将油滴连接到一起，同时聚合物分子可以压缩液滴表面的双电层，从而有利于油滴的聚结；当聚合物的浓度大于300mg/L时，体系的黏度增大，油滴的运动速度减小，此时聚合物分子占满油滴表面，表现出空间位阻作用，从而使油滴的稳定性增强，不利于油滴的聚结。     

Droplet composition affects the rate of oxidation of emulsified ethyl linoleate

Our objective was to study the influence of droplet composition on the rate of lipid oxidation in emulsions. A series of oil-in-water emulsions stabilized by a nonionic surfactant (Tween 20) was studied. These emulsions had the same total oil concentration (5 wt%) and initial droplet diameter (0.3 μm), but contained droplets with different ratios of ethyl linoleate (substrate) andn-tetradecane (inert diluent). Lipid oxidation was measured as a function of time by three different methods: gas-chromatographic determination of residual substrate; ultraviolet-visible spectrophotometric determination of conjugated dienes; and measurement of aqueous thiobarbituric acid-reactive substances. All three methods showed similar trends for emulsions of similar composition. The progress of lipid oxidation in the emulsions was dependent on the concentration of ethyl linoleate in the emulsion droplets. At low concentrations (1% oil as substrate), oxidation proceeded at a relatively slow and constant rate. At intermediate concentrations (20%), the oxidation rate was rapid initially and then slowed down with time. At high concentrations (100%), the oxidation rate was slow at first, and then increased with time. An explanation of our results is proposed in terms of the distribution of substrate molecules between the droplet interior and interface, and the ingress of aqueous radicals into the emulsion droplets.     

微通道内纳米颗粒对液滴聚并的影响规律

Pickering 乳液是纳米颗粒稳定的液液两相体系,微流控技术是制备单分散Pickering 乳液的有效方法,而含有纳米颗粒体系在微通道内的液滴聚并规律是该实施方法的关键科学问题之一。以正辛醇为连续相,水为分散相,研究了六边形扩大微通道内液滴碰撞过程,发现了液滴聚并、碰撞不聚并和不相互接触3 种流动状态,研究了流量、颗粒浓度和颗粒亲疏水性对于液滴聚并率的影响规律,分析了颗粒在液膜排空过程中的作用机理。     

ABA low molar mass triblock copolymers in reverse emulsions: A rheological study

The effect of blocks length and molar mass of ABA triblock copolymers on the rheological behavior of water in oil (w/o) emulsions was investigated. Emulsion parameters such as water droplet concentration (and droplet size) of a series of inverted emulsion systems were evaluated. All copolymer/emulsion systems studied showed a non-Newtonian behavior, and the presence of the copolymer in the emulsion system led to an increase of the low shear viscosity when the size of the midblock of the copolymer was in a specific size range. This suggests the formation of a transient network through the interconnection, by the copolymer, of the smaller water droplets present in the emulsion. Consequently, the systems behave as w/o emulsions containing reversibly crosslinked oil-soluble polymers in the continuous phase, resulting in a pronounced shear thinning behavior. For the different emulsions studied, the relative viscosity increased, with few exceptions, with increasing droplet concentration. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012